Testing prime focus digiscoping setups

[JGobeil]

Paul Corfield has started a thread last November called "Some digiscoping experiments with a DSLR". It has been extremely popular and is now in its 15th page. Paul and a few others have experimented with prime focus digiscoping and the results are quite fantastic. Using low cost astro refractor telescopes, very high magnification levels have been reached with good quality results. 100X seems possible under good conditions, and possibly more.

Lately, we have been working on a way to test those setups. We want a standard way to test different prime focus digiscoping setups to better understand the effect of adding teleconverters, barlows and extenders, stand alone or in series. This should allow us to evaluate different components for digiscoping use and to find out the best way to use them.

This thread has been opened to display and discuss those results.
To begin, we will test only the most simple setup possible: a refractor scope directly connected to a DSLR. This will allow us to optimize our testing protocol so that we become able to meaningfully compare different setups and options. After this initial stage, we will experiment with teleconverters, barlows and spacers, still in prime focus digiscoping only.

You are invited to participate with us. THERE IS ONLY ONE RULE: YOU MUST ABIDE BY THE PROTOCOL. If you feel that changes should be made, indeed suggest them but don't make changes on your own. We must compare apples with apples...

Feel free to use this protocol and the suggested target for your own resolution tests with other types of digiscoping. But please, POST ONLY PRIME FOCUS DIGISCOPING RESULTS ON THIS THREAD. Prime focus digiscoping is a DSLR directly connected to a telescope, without an eyepiece.

Version 1.0 of the testing protocol is described in the next post.

Regards
Jules Gobeil

[JGobeil]

Prime focus digiscoping protocol - V. 1.0
(Revised 08.07.02 20:00 EST)

PLEASE FOLLOW EXACTLY ALL THE INSTRUCTIONS IN THIS PROTOCOL AND DO NOT CHANGE ANYTHING. We won’t be able to compare meaningfully if we don’t use the EXACT same settings.


1- To begin this experiment, the test will be limited to a DSLR connected directly to an astro refractor scope. Nothing else: no teleconverters or barlows. Use spacers ONLY if they are required to get the target in focus. As soon as we are satisfied with the protocol we will open it to other setups.

2- The DSLR must be set to its standard settings. Of particular interest is the internal sharpness setting which should be set at the DEFAULT VALUE. It should be set at its maximum megapixel value if any choice is offered.

3- The target to be used is a standard ISO 12233 test chart. The file containing the target in JPEG form is available here. Right click on the image and copy.
http://julesgobeil.com/private/ISO_12233-reschart%20-%20resized-a.jpg

Only this file should be use as a source for the target. This target has those dimensions:
10.0 x 5.65 inches (254.0 x 143.51 mm) at 300 pixels/inch (118.11 pixels/cm). The complete image should be included in the target, do not crop out anything.

This size will fit A4 and Letter size paper with an adequate margin for all printers. After printing, the dimensions should be checked to make sure they are the same as the original file.

4- Find an adequate place to photograph the target under sunny conditions with little or no wind. Put the target on a firm background like a cardboard box or a piece of wood and fix it solidly so that it doesn’t wobble and its surface is perfectly flat. You must put it at a distance where the target will exactly fill the width of the viewfinder – no more, no less. The sun should be facing the target – behind your back when you take the picture. Make sure that the target is perfectly vertical and that the camera is at the same height as the target. Use a sturdy tripod and head - lock everything so it doesn’t move.

5- If possible use mirror lock-up and timer activated shutter or remote cable. Set the camera at ISO 400 and adjust the shutter speed for proper exposure. Take the photograph using RAW if it is available – if not, use JPEG at the highest resolution possible. Focus with extreme care and take 3 pictures, keeping the one with the best resolution.

6- Resize the COMPLETE photograph of the target to 800 megapixels wide and convert to JPG if you shoot RAW. DO NOT CROP AND DO NOT PROCESS IN ANY WAY. NO SHARPENING PLEASE ! Attach this picture to your post (Picture 1).

7- Using the photograph you made in step 5 (before resizing), Make a 800x800 pixels crop of the middle top portion of the target in your picture which is marked by a square, exactly as shown below. Convert it to JPG, no compression. Also attach this picture to your post (Picture 2).

Here is how it is done in Photoshop:
Start with your picture before resizing to 800 pixels (after Step 5)
Select the Crop Tool
Use those parameters (top left of screen, below the menus)
- Width: 800
- Height: 800
- Resolution: leave value empty and select Pixels/inch
Select the area with the mouse – it will be square
Press Enter to select
Verify that it is 800 x 800 pixels (Menu: Image / Image size)
Save it as picture2.jpg , no compression

8- Using the photograph you made in step 5 (before resizing), Make a 800x800 pixels crop of the lower right portion of the target in your picture which is also marked by a square, exactly as shown below. Convert it to JPG, no compression. Also attach this picture to your post (Picture 3).

9- Studying the target, evaluate the BEST resolution number. This is the highest number where you can see WHITE SPACE BETWEEN ALL FIVE LINES.

10- Publish your picture with the following information:

Make and model of DSLR:
Make and model of scope:
Type, make and model of camera adapter:
Length of spacer needed to reach focus:
Focal length of complete setup in mm:
Measured distance between target and telescope in meters:
Evaluated resolution number:
Speed setting of camera:
ISO:
Original picture format (RAW, JPG) and resolution (mpx)
Date and time:
Weather conditions (sun and wind):
Other pertinent information:

Pictures 1,2 and 3:

[ostling41]

This is a laudable project, and I hope it gets a long run. I don't currently have a DSLR or an astro scope -- I cannot be in the early group of participants but I'll be reading this thread to decide what to buy.

I was confused by your statement that 100x magnification is obtainable. I take this to be equivalent to the view of a 5000mm lens. Is that really possible with no eyepiece or camera lens?

[Paul Corfield]

This is a laudable project, and I hope it gets a long run. I don't currently have a DSLR or an astro scope -- I cannot be in the early group of participants but I'll be reading this thread to decide what to buy.

I was confused by your statement that 100x magnification is obtainable. I take this to be equivalent to the view of a 5000mm lens. Is that really possible with no eyepiece or camera lens?

Yes, 5000mm is easily obtainable using either teleconverters, barlow or both combined. I've never tried a 5X barlow but on a 600mm scope it would equate to 4800mm with a 1.6X crop factor. I've had my own setup out to beyond 7000mm using teleconverters combined with a barlow but in reality you would rarely need to go that far. 1000-4000mm would cover most situations I think.

Paul.

[Paul Corfield]

Right, here's my images using just prime focus. For the resolution score I went for 11 but looking at my printout the lines start to bleed together at around 11-12 so it's going to be hard to score any higher because of the limitations in the printing. On other parts of the chart where it only goes up to 10 I can see white very clearly between the lines so I'd say 11 is an honest score.

Make and model of DSLR: Canon 450D
Make and model of scope: Skywatcher Evostar Pro 80ED
Type, make and model of camera adapter: T-Ring with 2" scope adapter, both unbranded
Length of spacer needed to reach focus: 85mm
Focal length of complete setup in mm: 960mm after crop factor of 1.6
Measured distance between target and telescope in meters: 6m 74cm
Evaluated resolution number: 11
Speed setting of camera: 1/1000 sec
ISO: 400
Original picture format (RAW, JPG) and resolution (mpx) RAW 12.2 million pixels
Date and time: 4th july 13:16
Weather conditions (sun and wind): Sunny, breezy but garden is sheltered.
Other pertinent information:

[Derry]

fine clear day today for my test,, can sure see the need for a macro focuser on the scope doing this,, used live view at 10X and even the slightest touch on the focuser was wild,, found the best of the photos taken,, can see higher line count on the original than on the reduced ones posted,,

Make and model of DSLR: Olympus E3
Make and model of scope: TeleVue TV85
Type, make and model of camera adapter: Olympus 4/3 to OM T mount
Length of spacer needed to reach focus: 50mm
Focal length of complete setup in mm: 1200mm (camers has 2X crop)
Measured distance between target and telescope in meters: 10.05m (33 feet)
Evaluated resolution number: 13 with 14 on the vertical
Speed setting of camera: 1/500 sec
ISO: 100
Original picture format: RAW then to JPEG, final 9.75 million pixels
Date and time: 2008-07-04 13:08:56
Weather conditions (sun and wind): Sunny, no clouds or wind
Other pertinent information:

[Derry]

when we use the spacer to allow focus and the shorter distance should that be figured into the over-all mm length of the scope,,??

I just used the scopes mm fl and the camera crop factor,, still in prime focus though,,

Derry

[Paul Corfield]

when we use the spacer to allow focus and the shorter distance should that be figured into the over-all mm length of the scope,,??

I just used the scopes mm fl and the camera crop factor,, still in prime focus though,,

Derry

The size of the spacer wont affect the magnification or the size of the image so it doesn't really need to be factored in. All it does alter how near or far you can focus.

Paul.

[JGobeil]

We got a rain storm when I was finally ready to test this afternoon. I tested anyway after dinner to find out if I was able to focus close enough - no problem with the Kenko set of spacers!. The sun was gone so I won't post but even with low light, I has a resolution around 11-12.

I also think that printing the target will be the biggest limitation. I can print 13"x19" here but most people can't. This why I resized to 10" but this was probably a mistake. What do you think ?

[Paul Corfield]

One way I suppose would be to take the most relevant parts from the test sheet and rearrange them to make our own sheet. That way they could be better positioned on the paper to allow them to be printed at the maximum size possible on A4. You could have the two parts that show resolution running length ways on the paper rather than top to bottom as they are now.

Paul.

[ostling41]

The usefulness of Picture 3 is questionable. Both Paul and Derry have posted Picture 3 images in which the lines spacings are visible all the way to the max resolution of 10. So the resolution at which failure occurs is not determined.

[edit] I've yet to print a target image in which the full resolution (20) is visible using a loupe. In fact, I don't think this max resolution is discernible in the posted jpeg.

[Paul Corfield]

The usefulness of Picture 3 is questionable. Both Paul and Derry have posted Picture 3 images in which the lines spacings are visible all the way to the max resolution of 10. So the resolution at which failure occurs is not determined.

[edit] I've yet to print a target image in which the full resolution (20) is visible using a loupe. In fact, I don't think this max resolution is discernible in the posted jpeg.

Picture 3 is a crop from the bottom right corner of the test image and is purely to see any softness etc at the far corner of the lens.

Paul.

[Derry]

was just looking (10X loupe) at my test chart printed on glossy photographic paper and the smallest resolution is in the 17 line area,, can see some in the 18 but after that the lines are really blending,,

Allan, I printed the test chart out on legal (8.5 X 14") letter quality paper and the 20 lines are "barely" readable with the loupe,, that is the largest size I have to print and cannot handle any wider paper,,

with paper and printer abilites differing I agree that we need a larger or different chart, perhaps the Coke can mentioned prior or something we all could obtain that is printed the same to remove our printers limitation(s),, at least we would all be shooting an exact item,,

any thoughts,,


I also notice the right side of my photos are a tad more out of focus that the left,, apparently the chart was not at a true 90 degrees to the scope,, an error on my part (??) as I have never seen that in any other photos taken through the scope,, set up is very critial as we are dealing with a very shallow DOF as we all are aware,,

Derry

[JGobeil]

I'm working on a new test chart. I should post it later today for your opinion. I think that your evaluations of the resolution are a bit on the optimist side - don't forget that you should be able to see white between all lines.

Regards
Jules

[JGobeil]

Here is a tentative for a new version of the target. It makes it easier to evaluate the resolution, specially when we will be working at high magnification. and only one post will be required instead of 3. However, it does not change anything - the lines and the spaces are just bigger.

Printing the target on an inkjet at 300ppi, I easily see all lines and spaces at the maximum 20 resolution.

Taking a full screen picture at 896mm, I get a very net 20 resolution.

Right click on the image and copy the file - you should get a 10"x7.5" 300ppi image.
http//julesgobeil.com/private/iso_12233-mod-jules-v1_0.jpg (http://julesgobeil.com/private/iso_12233-mod-jules-v1_0.jpg)

Comments please !
Jules

[Derry]

Jules, printed the chart out at 300 dpi and can see the lines out to the 20 even on the low grade letter paper I have,, you can see the texture in the first two photos below,, chart looks fine,,

took a couple macros with my P5000 for display,,

the last one is through my 10X loupe of the original test chart printed on glossy photo paper which show resolution in the 16 and 17 area,, sure could not capture it on the camera though,,

Derry


macro

------ of center ----------- upper right ----------- first test chart

[Paul Corfield]

I printed off the new chart today and did a test photo. Here's a crop showing the middle portion with white space between all the lines. I think the new chart is pretty good and should serve well for the tests at higher magnification.

All details for this image were the same as the fist chart I posted apart from shutter speed which was 1/640sec.

Paul.

[JGobeil]

Ok, here is the new Version 2.0 protocol with the revised target. Let's hope it is the last revision...

Besides the new target, I have removed the mandatory requirement for those elements that are not required to compare meaningfully.


Prime focus digiscoping protocol - V. 2.0
(Revised 08.07.06 17:15 EST)

PLEASE FOLLOW EXACTLY ALL THE INSTRUCTIONS IN THIS PROTOCOL AND DO NOT CHANGE ANYTHING. We won’t be able to compare meaningfully if we don’t use the EXACT same settings.


1- To begin this experiment, the test will be limited to a DSLR connected directly to an astro refractor scope. Nothing else: no teleconverters or barlows. Use spacers ONLY if they are required to get the target in focus. As soon as we are satisfied with the protocol we will open it to other setups.

2- The DSLR must be set to its standard settings. Of particular interest is the internal sharpness setting which should be set at the DEFAULT VALUE. It should be set at its maximum megapixel value if any choice is offered.

3- The target to be used is derived from a standard ISO 12233 test chart. It has been modified so that everybody can print it with a standard home printer and resolve the finest resolution. The file containing the target in JPEG form is available here. Right click on the image and copy.
http://julesgobeil.com/private/digiscoping%20target%20v2_0.jpg

Only this file should be use as a source for the target. This target has those dimensions:
10.0 x 7.7527 inches (254.0 x 191,18) at 300 pixels/inch (118,11 pixels/cm). The complete image should be included in the target, do not crop out anything.

This size will fit A4 and Letter size paper with an adequate margin for all printers. After printing, the dimensions should be checked to make sure they are the same as the original file.

4- Find an adequate place to photograph the target under sunny conditions with little or no wind. Put the target on a firm background like a cardboard box or a piece of wood and fix it solidly so that it doesn’t wobble and its surface is perfectly flat. You must put it at a distance where the target will exactly fill the width of the viewfinder – no more, no less. The sun should be facing the target – behind your back when you take the picture. Make sure that the target is perfectly vertical and that the camera is at the same height as the target. Use a sturdy tripod and head - lock everything so it doesn’t move. These recommendations about sun, wind and setup stability are not mandatory but are most important to ensure a sharp picture.

5- If possible use mirror lock-up and timer activated shutter or remote cable. Set the camera at ISO 400 (not mandatory) and adjust the shutter speed for proper exposure. Take the photograph using RAW if it is available – if not, use JPEG at the highest resolution possible. Focus with extreme care and take a few pictures, keeping the one with the most accurate focus.

6- Resize the COMPLETE photograph of the target to 1024 pixels wide and convert to JPG if you shoot RAW. DO NOT CROP AND DO NOT PROCESS IN ANY WAY. NO SHARPENING PLEASE ! Attach this picture to your post. If the file is too big to upload, reduce the JPEG quality (In Photoshop, set it to 8).

7- Studying the target, evaluate the BEST resolution number. This is the highest number where you can see WHITE SPACE BETWEEN ALL FIVE BLACK LINES.

8- Publish your picture with the following information:

Make and model of DSLR:
Make and model of scope:
Type, make and model of camera adapter:
Length of spacer needed to reach focus:
Focal length of complete setup in mm:
Measured distance between target and telescope in meters:
Evaluated resolution number:
Speed setting of camera:
ISO:
Original picture format (RAW, JPG) and resolution (mpx)
Date and time:
Weather conditions (sun and wind):
Other pertinent information:

Target resized at 1024 px wide attached.

[JGobeil]

I took the test today. Max resolution easily resolved. I think we should open the test to teleconverters and barlows.

Jules

Make and model of DSLR: Canon 20D
Make and model of scope: Astro-Tech AT80ED 80mm f/7 ED doublet refractor
Type, make and model of camera adapter: CNC Supply EOS 2" Adaptor
Length of spacer needed to reach focus: Kenko 68mm set
Focal length of complete setup in mm: 896mm
Measured distance between target and telescope in meters: 7,26 m. - 23.8"
Evaluated resolution number:20 max
Speed setting of camera: 1/200
ISO: 400
Original picture format (RAW, JPG) and resolution (mpx) RAW - 8mpx
Date and time: 08.07.07 19:00
Weather conditions (sun and wind): cloudy bright - no wind - extremely humjid
Other pertinent information:

[Paul Corfield]

Time for a couple of teleconverter tests. I added in an extra category for teleconverter/barlow type, is that OK?

Make and model of DSLR: Canon 450D
Make and model of scope: Skywatcher Evostar Pro 80ED
Make and model of converter or barlow: 1.5X Vivitar Teleconverter
Type, make and model of camera adapter: T-Ring with 2" scope adapter, both unbranded
Length of spacer needed to reach focus: 60mm
Focal length of complete setup in mm: 1440mm after crop factor of 1.6
Measured distance between target and telescope in meters: 12m 19cm
Evaluated resolution number: 20
Speed setting of camera: 1/160sec
ISO: 400
Original picture format (RAW, JPG) and resolution (mpx) RAW 12.2 million pixels
Date and time: 8th july 09:53
Weather conditions (sun and wind): Sunny, breezy but garden is sheltered.
Other pertinent information:

[Paul Corfield]

2X Aico 7 element teleconverter performed very nicely for this one. Sharper than the 4 element 1.5X Vivitar I used on the last test.

edit - As a comparison to the unprocessed RAW file I also posted a full size crop showing the RAW file after processing in Adobe Lightroom. You can see how well the RAW file comes up after some very basic editing. The Unprocessed RAW files in the Canon 450D can look slightly soft I think but the detail is there to be brought out.

Make and model of DSLR: Canon 450D
Make and model of scope: Skywatcher Evostar Pro 80ED
Make and model of converter or barlow: 2X Aico 7 element Teleconverter
Type, make and model of camera adapter: T-Ring with 2" scope adapter, both unbranded
Length of spacer needed to reach focus: 60mm
Focal length of complete setup in mm: 1920mm after crop factor of 1.6
Measured distance between target and telescope in meters: 15m 13cm
Evaluated resolution number: 20
Speed setting of camera: 1/60sec
ISO: 400
Original picture format (RAW, JPG) and resolution (mpx) RAW 12.2 million pixels
Date and time: 8th july 10:08
Weather conditions (sun and wind): Sunny but target was in shade, breezy but garden is sheltered.
Other pertinent information:[/QUOTE]

[Paul Corfield]

For this one I used my cheap, unbranded 2X barlow. Worked very well, nice and sharp even on the unprocessed images. A little bit of CA but that is understandable with such a cheap barlow and inferior multi coatings. CA not noticeable when photo is reduced in size. Compared to my 2X teleconverter I had to move the scope around 1m closer to the target which suggests the barlow is a little under its stated 2X power.

Make and model of DSLR: Canon 450D
Make and model of scope: Skywatcher Evostar Pro 80ED
Make and model of converter or barlow: 2X barlow, unbranded and mounted inside old teleconverter housing
Type, make and model of camera adapter: T-Ring with 2" scope adapter, both unbranded
Length of spacer needed to reach focus: 60mm
Focal length of complete setup in mm: unknown, slightly less than 2X teleconverter
Measured distance between target and telescope in meters: 13m 83cm
Evaluated resolution number: 20
Speed setting of camera: 1/800sec
ISO: 400
Original picture format (RAW, JPG) and resolution (mpx) RAW 12.2 million pixels
Date and time: 8th july 16:23
Weather conditions (sun and wind): Sunny with target in full sunlight, breezy but garden is sheltered.
Other pertinent information:

[mouz59]

Hey guys, i"m Mike- Vandit recommended me to this site from Canon POTN.

I too, have been testing optics-

I will gladly contribute to this thread once i shoot some pics of your target, however, i personally think the target is on the weak side.

I use the Koren 2003 lens test chart- it is a PRESSURE COOKER for ANY lens! goes all the way from 0-200lp/mm across a 25cm spread.

a pic of the Koren target shot with my Astro-Physics telescope:

Canon EOS 1d Mk III
Astro-Physics Starfire 102
Astro-Physics prime focus camera adapter PFCT
813mm f8
16.5 Meters distance
ISO 100
RAW file
Shot in my basement

Resolved >100 LP/MM!! - actually went OFF my reference chart! - I need to adapt the chart for these high end optics. In comparison, the 200mm F2 L canon was around ~86LP/MM.

[mouz59]

The web page of the Koren test chart..

http://www.normankoren.com/Tutorials/MTF5.html

[ostling41]

The web page of the Koren test chart..

http://www.normankoren.com/Tutorials/MTF5.html

This is a very impressive chart. It goes to a point of where no lens system can be expected to resolve, showing a definite delineation between "go" and "no go." It allows calculation of MTF.

Many of us may not have an inkjet good enough for printing it, though.

[Paul Corfield]

This is a very impressive chart. It goes to a point of where no lens system can be expected to resolve, showing a definite delineation between "go" and "no go." It allows calculation of MTF.

Many of us may not have an inkjet good enough for printing it, though.

They do versions for different inkjet printers and also corrected versions to allow for 0.25 of ink spread. Should be able to get something that prints fairly well.

I agree, looks like a nice chart.

Here's the link again seeing as we are on a new page.

The web page of the Koren test chart..

http://www.normankoren.com/Tutorials/MTF5.html


Paul.

[Derry]

Mike, great read on that web page on testing lens,, is that your AP Starfire add on Astromart,, LOL

how do we know what our HP inkjet printer is able to print at for selecting the correct chart,,??

Derry

[Paul Corfield]

Mike, great read on that web page on testing lens,, is that your AP Starfire add on Astromart,, LOL

how do we know what our HP inkjet printer is able to print at for selecting the correct chart,,??

Derry

For inkjet printers it says to use the .25 correction. For the HP printer you would need -

5mm, 1.5, 0.25, 5906 which is http://www.normankoren.com/Tutorials/Lenstarg_50_5906p_15g_25is.png

Paul.

[Derry]

tried the Korean test chart,, did two photos as wanted to see if the resolution was better in the center of the scope, see center photo,, use the 10X on live view on the camera for final focus,,

line readings on my original photos,, have 24" HD monitor,,
full test chart photo I can read to about 110 lines,,
on the second photo I can read to the 200 lines,, see third photo which is a small area crop from the center photo,,

reducing them to post here the resolution certainly suffers,,

Make and model of DSLR: Olympus E3
Make and model of scope: TeleVue TV85
Type, make and model of camera adapter: Olympus 4/3 to OM T mount
Length of spacer needed to reach focus: 50mm
Focal length of complete setup in mm: 600mm (camers has 2X crop)
Measured distance between target and telescope in meters: 10.m
Evaluated resolution number:110 lines to 200 on original photos
Speed setting of camera: 1/200 sec
ISO: 100
Original picture format: RAW then to JPEG, final 9.56 million pixels
Date and time: 2008-07-08 14:00
Weather conditions: partly sunny, temp 92F and RH at 86%, kind of muggy

[mouz59]

No, my Starfire isn't on Astromart- there is one on there for $400USD less than what i bought mine for, which makes me kinda jealous!

I'm attaching a copy of my recent science fair project which outlines my procedure for testing. It's not the same as the Koren test chart, but it's alot simpler. - and will save me alot of time typing my procedure out on here...

oh, and concerning the printing- i printed mine out straight with my Canon iP6700D on Brilliant Luster paper from Calumet Photo. I might try it on a fine art or high resolution paper here soon from Hahnemuhle- I'm really digging' their fine art canvas paper.

i'll post all my data from all tested lenses in the next day or two. In the mean time, keep the tests coming!

Mike

[mouz59]

Thats some INSANE resolution!!! - I think the smaller sensor with more megapixels plays a large part.

kinda scared that a TV85 can out-resolve my Starfire.... thats scary... really scary. - and not even possible, right? Dawes Limit... it has to be the crop sensor and the distance.

whatever, mine is "vintage" anyway ; )

tried the Korean test chart,, did two photos as wanted to see if the resolution was better in the center of the scope, see center photo,, use the 10X on live view on the camera for final focus,,

line readings on my original photos,, have 24" HD monitor,,
full test chart photo I can read to about 110 lines,,
on the second photo I can read to the 200 lines,, see third photo which is a small area crop from the center photo,,

reducing them to post here the resolution certainly suffers,,

Make and model of DSLR: Olympus E3
Make and model of scope: TeleVue TV85
Type, make and model of camera adapter: Olympus 4/3 to OM T mount
Length of spacer needed to reach focus: 50mm
Focal length of complete setup in mm: 600mm (camers has 2X crop)
Measured distance between target and telescope in meters: 10.m
Evaluated resolution number:110 lines to 200 on original photos
Speed setting of camera: 1/200 sec
ISO: 100
Original picture format: RAW then to JPEG, final 9.56 million pixels
Date and time: 2008-07-08 14:00
Weather conditions: partly sunny, temp 92F and RH at 86%, kind of muggy

[Derry]

Mike, know about Dawes limit,, my 3.5 Q has exceeded it several times in past years splitting doubles on a good night,, there has been some bright sunny days that the Q can resolve more detail than my TV85,, was looking at a small hex head nut on a power transformer about 1/4 mile away,, could see it with the TV85 but not definer it as a hex head,, the Q is from the early 1990s and my TV85 is about nine years old,,

as you can see there is roll off when looking at the first photo toward the edges,, have never been able to see that while observing or in any of my bird photos,, guess the verticle lines are tougher to resolve than a bunch of bird feathers,,

have an adapter arriving tomorrow to mount the E3 and one of my camera lens (Oly 50mm) behind the various TV eyepieces for some real high power,, would imagine air disturbance is going to play a roll when we get into those test,,

interesting reading on the science fair project,, nice work,,

Derry

[mouz59]

3.5Q ?? Questar 3.5? not sure what your referring to, sorry.

anyway, I'm gonna re-shoot my target at a closer distance and see what i get. should be alot better resolution (but not necessarily fair). also, the E-3 has MUCH smaller pixels- 4.7u as opposed to 11u ... and you also are talking about a much smaller chip- and we dont know what kind of in camera processing is going on. Regardless, the photos are SHARP! Maybe i should rent a E-3 from Calumet and see my results. - although the 40d has a 5.7u pitch, which is alot closer.. and my buddy has a 40d. Hopefully i can get him over by Sunday and get the results up.

yeah, Oly lenses on the back of the scope? that'll be interesting for sure. - probably will hurt your image quality, but should get you VERY close to distant objects, which will be interesting. Hope you post up some pics!

[Derry]

Mike, yes the Q is a Questar,, this is my second one,,

also had a 12.5" f5 Portaball when we lived in Florida,, very interesting scope and what resolving power with those Zambuto mirrors,, could see the central star in M57 (Ring Nebula) on a good cold night,,

will be interesting to mount the Oly glass on the scope,, they make some extremely good lens in the pro line,,

Derry

[mouz59]

Not surprised- Questar is probably (i dont know for sure, never used one) on par with AP- there all custom built hand figured, right? kinda wanted one back in the day, but I'm content with what i have. The Portaball sounds intriguing too- saw one at a astro convention once, adn i must say, i was impressed.

anyway, the resolution figures in my project are crap because i shot outside on a windy day. I just went with it anyway because it proved a point. The figurees i'll be posting soon are all MUCH better data- shot in the basement, hence a much more controlled environment.

[Paul Corfield]

oh, and concerning the printing- i printed mine out straight with my Canon iP6700D on Brilliant Luster paper from Calumet Photo. I might try it on a fine art or high resolution paper here soon from Hahnemuhle- I'm really digging' their fine art canvas paper.

Mike

I printed my test chart onto Hahnemuhle Torchon 285gsm paper using my Epson 2100. Comes up really nice. Been using the Hahnemuhle paper for years and really love the quality it produces.

Regarding lenses through eyepieces, in all the tests I've tried the teleconverters have always beaten lenses by quite a bit as far as details resolved, probably because of the amount of glass involved in eyepieces and lenses. With lenses and eyepieces the light really sufferes for birding purposes and the magnification is on a similar level to that of teleconverters. The weight is a major issue too. Just sold all my lenses on ebay to pay for more barlows/teleconverters. :t:

Paul.

[Paul Corfield]

Here's a 100% crop of the Koren chart taken through my Skywatcher 80ED with the Canon 450D. Chucking it down with rain here so I had to take this one indoors which was lit with just a couple of bulbs. Range was 6m 20cm which is a similar range to my photo of old chart. Resolved the lines all the way to 200.

Paul.

[JGobeil]

Duplicate post - see below. Sorry....

Jules

[JGobeil]

Hey guys, don't you think we are a bit fast !!!

We can't change the target in the protocol at will. Let's not forget that the reason for this protocol is to define a standard way of testing digiscoping setups.

So far, we have tried 2 targets - the standard ISO 12233 target and one that I made derived from the first one. IMO, both are inadequate: the first one is impossible to print with a home printer and the second does not allow small enough resolutions as demonstrated by Paul's 2X barlow and 2X teleconverter that still resolve maximum resolution with his scope and camera.

Should we use the Koren target ? I am not sure !
Can it be printed at home ?
Can it measure resolution in the corners ?
Can it evaluate chromatic aberration, a most important characteristic ?
This target is copyrighted !

I don't mind changing the protocol - this is OUR protocol, not MINE - I only had the privilege of writing it (and I'm perfectly willing to give the job to somebody else...) !

[Paul Corfield]

I quite like the chart we have now as it pretty much covers everything that we want to test. All my tests so far have been under 20m which isn't really taxing the scope or any of our scopes so I guess we need to increase the range. I would normally use a 2X converter at around 30m and beyond. Maybe we should get to the point where the test chart fills the frame and then move an additional pre determined distance, say 15 or 20m or maybe find out at what range the current chart starts to fail and use that as a guide.

The Koren chart is ok to print and has some very fine lines but for what we want to do it's unsuitable in that the finest lines are way off to one side and it doesn't test all the corners for softness. Plus as we have already shown it's still fairly easy to resolve all the lines at the ranges we are already experimenting at.

edit - comparing the lines on our current chart with the Koren one I'd say our chart is around the 150 range so it's already testing quite fine detail.

Paul.

[JGobeil]

I quite like the chart we have now as it pretty much covers everything that we want to test. All my tests so far have been under 20m which isn't really taxing the scope or any of our scopes so I guess we need to increase the range. I would normally use a 2X converter at around 30m and beyond. Maybe we should get to the point where the test chart fills the frame and then move an additional pre determined distance, say 15 or 20m or maybe find out at what range the current chart starts to fail and use that as a guide.

The Koren chart is ok to print and has some very fine lines but for what we want to do it's unsuitable in that the finest lines are way off to one side and it doesn't test all the corners for softness. Plus as we have already shown it's still fairly easy to resolve all the lines at the ranges we are already experimenting at.

edit - comparing the lines on our current chart with the Koren one I'd say our chart is around the 150 range so it's already testing quite fine detail.

Paul.

Very interesting comments Paul. Let's see what the others have to say.

[Derry]

Jules, your doing a great job and I believe we all agree on the set up,, just another test chart to look at that we were not aware of,, so we shot it and found the good and the bad,,

my only thoughts are you guys with the high price spread (printers) and me trying to work a four year old HP inkjet and normal letter paper,, |:D|

the main thing I was questioning was how we are figuring the final mm of our set ups and the more I find to read the cameras X factor should not be a part of our magnification multiplier,, it needs to be listed but not in the mm calculation,, my pennys worth,,

so we are staying with the second chart that test all surface areas of the lens,,

what is our roadmap from this point,, I believe we all have a variety of optics to use but may not be the same set up so final output will vary,, I see Paul has several barlows, I recently sold all my TeleVue barlows as I was not using them in my limited astro activity,,

I'm ready to roll,,

Derry

[JGobeil]

Jules, your doing a great job and I believe we all agree on the set up,, just another test chart to look at that we were not aware of,, so we shot it and found the good and the bad,,

my only thoughts are you guys with the high price spread (printers) and me trying to work a four year old HP inkjet and normal letter paper,, |:D|

the main thing I was questioning was how we are figuring the final mm of our set ups and the more I find to read the cameras X factor should not be a part of our magnification multiplier,, it needs to be listed but not in the mm calculation,, my pennys worth,,

so we are staying with the second chart that test all surface areas of the lens,,

what is our roadmap from this point,, I believe we all have a variety of optics to use but may not be the same set up so final output will vary,, I see Paul has several barlows, I recently sold all my TeleVue barlows as I was not using them in my limited astro activity,,

I'm ready to roll,,

Derry

Thanks for the comments Derry.

Your inkjet printer may not be a problem. I have 2 Canon printers: a i9900, 13x19" and a i960 8.5x14". They were purchased 3 or 4 years ago. In order to get good results, I use high res paper that you can easily get at Staples or similar stores. I use Epson High Quality Ink Jet Paper in 8.5x11" format sold in packages of 100 sheets - cheap and very good. I easily resolve the 200 max lp/mm of the Koren chart.

I answered your concern about the camera crop factor in the other thread "Some digiscoping experiments with a DSLR". Just my opinion of course.

IMO, our roadmap is to keep investigating the best way of using chart no. 2 - the one in Protocol V 2.0. I think we need to answer these 3 questions:
1- What to do with the crop factor ?
2- At what distance should we take the picture ?
3- What should be the "effective resolution" formula used to compare setups ?

I strongly suggest we limit our testing to Prime Focus Digiscoping for now. DSLR and scope with magnifying devices in between - barlows, teleconverters and spacers. No eyepieces or camera lenses. Once we are satisfied with the protocol and the results, it will be time to open it to all digiscoping.

Regards
Jules

[bluedubius]

One more question before I conduct my test (when weather permits). On the version 2.0 protocol it states that the target should measure 10" x 7.7527" when printed. When I print the V 2.0 target chart and print I get a 10" x 7.5" target when measured between the black borders. Which is it?

Rick

[mouz59]

The Koren chart is ok to print and has some very fine lines but for what we want to do it's unsuitable in that the finest lines are way off to one side and it doesn't test all the corners for softness. Plus as we have already shown it's still fairly easy to resolve all the lines at the ranges we are already experimenting at.
Paul.

^^well yeah, for those of us with cameras that have pixels way smaller than 10u ... :-C

This is useful..
http://fourthirds-user.com/2007/10/comparing_the_olympus_e3_to_its_competitors.php

maybe we need to standardize on a camera? The smaller APS-C and 4/3 chips seem to be what everyone's using. I'm thinking that for any reasonable comparison, you have to have at least a APS-C camera... I myself have access to a Canon 40d.

I personally think that both targets should be used. I'm thinking about buying a project board and printing out various targets (like the Koren and ISO) and compiling them as a "super-target." Also, backing it up a bit will definetley put stress on the optic. My basement is almost 90ft long (what like ~30M??) so that could be a control (for me, anyway)- shooting outside at a much farther distance (100M ? that would definatley be pushing it) would be interesting.

[JGobeil]

One more question before I conduct my test (when weather permits). On the version 2.0 protocol it states that the target should measure 10" x 7.7527" when printed. When I print the V 2.0 target chart and print I get a 10" x 7.5" target when measured between the black borders. Which is it?

Rick

Same thing. My error - the exact dimension is 7.527. I will correct in the next version.

[JGobeil]

^^well yeah, for those of us with cameras that have pixels way smaller than 10u ... :-C

This is useful..
http://fourthirds-user.com/2007/10/comparing_the_olympus_e3_to_its_competitors.php

maybe we need to standardize on a camera? The smaller APS-C and 4/3 chips seem to be what everyone's using. I'm thinking that for any reasonable comparison, you have to have at least a APS-C camera... I myself have access to a Canon 40d.

I personally think that both targets should be used. I'm thinking about buying a project board and printing out various targets (like the Koren and ISO) and compiling them as a "super-target." Also, backing it up a bit will definetley put stress on the optic. My basement is almost 90ft long (what like ~30M??) so that could be a control (for me, anyway)- shooting outside at a much farther distance (100M ? that would definatley be pushing it) would be interesting.

I don't think we should do that. The trend is towards full frame sensors. Nikon just introduced the D700 and Canon will be introducing a prosumer full frame DSLR this fall in the 2-3000$ range. We must keep it simple and universal, that way, it will be adequate for everybody including those with P&S cameras.

[mouz59]

yes, but how many of us have the larger chips? It seems that that most have the smaller- which obviously outresolve the larger. I've done alot of testing with the Koren chart, and i NEVER hit 200lpmm! i'm pretty depressed, actually, that a Mk III was outdone by a digi rebel (350d)

actually, if you really want full frame, i still have 2 rolls of Kodak TP2415... could shoot that with my F-1 and have it drum scanned...

just to give you an idea of how bad an idea that would be, i attached a picture of my target shot with a AP Starfire 130EDT (much better than pretty much anything mentioned so far- refractor wise) and a EOS 1Ds Mk III.

it's AWFUL.

[Paul Corfield]

i'm pretty depressed, actually, that a Mk III was outdone by a digi rebel (350d)


The photo I posted was with the new 450D if that makes you feel a little bit better.

Paul.

[mouz59]

sorry for misspeaking^^^

[Paul Corfield]

Mike, can you post an unresized crop from your photo showing the detail at the 200lpmm end?

Cheers,
Paul.

[Derry]

Mike, one advantage my E3 may have is using live view which I can zoom in to 10X for fine focusing which is very critical,, I'm thinking about a finer focus control for the scope as at 10x on live view a slight amount of presure makes a big difference with such a shallow dof,, it does not even feel like I am turning the knob but I can see the results on the cameras screen,,

have seen photos from that model of canon and you can count the fine hairs on the models head so the camera and your AP scope should have no issues with the 200 line resolution,,

Derry

[Derry]

just posted this on the other thread,,

think we are going to have to draw the line in the sand somewhere and go with what we have,, just reading an article on how much AA filtering Olympus does compared to other brands which has negative impact on resolution,, you just mentioned the Oly E420 which seems to have even more AA as it is rendering some soft photos from the same lens, owners had sharper photos with on prior bodies,,

the more we read the more data to place into the coffer and digest,,

our end result is trying to resolve some fine lines at given distance,, either the equipment can or it cannot,, when we get to the longer distance air turblance is going to have great impact,, how do we control or calculate that into obtaining a sharp image,,

we have the base that Jules prepared with test chart(s),, lets shoot them at prime filling the screen and then start working at given distances to see what we can resolve on the lines at given X mags,,

if we want to use the cameras factor into the calculation I am fine with it,,

Derry

[Paul Corfield]

Air turbulence is dependant on the weather and if it's present then you can see it in the camera viewfinder. The image will shimmer or come in and out of focus and all sorts of other funny stuff. If that's the case then wait for a day when conditions are more favourable.

If the air was like that when trying to photograph a bird then you would have to either get closer to the bird or wait for another day so it's similar with the test chart.

Paul.

[mouz59]

Mike, one advantage my E3 may have is using live view which I can zoom in to 10X for fine focusing which is very critical,, I'm thinking about a finer focus control for the scope as at 10x on live view a slight amount of presure makes a big difference with such a shallow dof,, it does not even feel like I am turning the knob but I can see the results on the cameras screen,,

have seen photos from that model of canon and you can count the fine hairs on the models head so the camera and your AP scope should have no issues with the 200 line resolution,,

Derry

yep- manual focus with live view- all new generation Canon's have it. i always critically focus at 10x.

anyway, i'm pretty convinced that it is camera shake. bogen 3047 head (what i was using) is only rated at ~17lbs. Starfire 130 is ~20.

i'll post up the pics resized later tonight or tommrow. got some important things happening right now- gotta read some Kurt Vonnegut for school tommrow : (

[JGobeil]

Cameras and air turbulence are indeed factors but in my book stability is also a huge factor. A solid and stable tripod/head combinaison, remote or timer triggering and even mirror lock-up in extreme cases, are a must for high magnification precision.

Try tapping with one finger on the scope and watch if there is the vibration in the viewfinder. My Benro C-328 carbon tripod with just 2 legs extended and Manfrotto 501HDV head are rock solid - no vibration at all. Add a remote trigger and I am in business.

When a setup does not bring the expected results, one must find what's wrong and change or fix that component. Unfortunately, it took me almost a year to realize that my Pentax scope was at fault. Now that I have the Astro-Tech refractor, it is a completely different world. Unfortunately, I didn't have time nor wx to fully test it yet but every photograph taken with it has been incredibly sharp.

Don't forget that the weakest link in a chain defines its strength... Don't neglect anything - camera, settings, scope, TC or barlow, tripod, head, wx, technique. That's how we will be able to achieve good results at high magnification. At 60X, the slightest movement or problem is multiplied by 60. Imagine at 100X...

[Paul Corfield]

Last night I was photographing the moon from my bedroom window and I was in the 3000mm region. One of the tripods legs was up against the bed frame and I was laying on the bed. Just my heartbeat could be detected as a steady vibration through camera viewfinder.

When I'm photographing from indoors, even my cat walking across the carpet a few feet away will be seen as quite a big vibration when looking through the scope. My old tripod that I've had for years is my weakest link and if I can get good results then anyone can. I'll upgrade it later in the year to a nice sturdy Manfrotto.

Paul.

[Paul Corfield]

Here's the test chart taken with the GSO 2" 2X ED Barlow. Best lens I've used so far. With postage it cost me £33 ($65) brand new from ebay.

3rd image is of the edited RAW file, included this as it shows so much detail.

Make and model of DSLR: Canon 450D
Make and model of scope: Skywatcher Evostar Pro 80ED
Make and model of converter or barlow: GSO 2" 2X ED Barlow
Type, make and model of camera adapter: T-Ring with 2" scope adapter, both unbranded
Length of spacer needed to reach focus: 70mm
Focal length of complete setup in mm: Approx 1920mm after crop factor of 1.6
Measured distance between target and telescope in meters: 15m 59cm
Evaluated resolution number: 20
Speed setting of camera: 1/100sec
ISO: 400
Original picture format (RAW, JPG) and resolution (mpx) RAW 12.2 million pixels
Date and time: 10th july 09:03
Weather conditions (sun and wind): Sunny but target in shade, breezy but garden is sheltered.
Other pertinent information: The barlow lens cell was removed from the barlow body and screwed into the 2" T-mount. The barlow body then becomes the extension tube used to achieve focus. So you get 2 pieces of equipment in one which is handy.

[Paul Corfield]

Took a photo of the Koren chart using the 2" GSO 2X ED barlow. Range was measured to 17m. Resolved all the way to 200.

2nd photo taken with 120mm extension tube between the barlow and the camera. Tested to see if resolving power would suffer. Easily resolved all the way to 200.

Paul.

[bluedubius]

I conducted the test run with the Celestron 80ED and Fuji S2 Pro DSLR today. Looks like similar results to other prime focus tests here.

Make and model of DSLR: Fuji S2 Pro
Make and model of scope: Celestron 80ED 80mm f7.5 (600mm fl)
Type, make and model of camera adapter: built-in to scope
Length of spacer needed to reach focus: appx 60mm
Focal length of complete setup in mm: 900mm
Measured distance between target and telescope in meters: 8 meters
Evaluated resolution number: 20 max
Speed setting of camera: 1/2000 sec
ISO: 200
Original picture format (RAW, JPG) and resolution (mpx) RAW 12mpx
Date and time: 07/11/2008
Weather conditions (sun and wind): sunny no wind
Other pertinent information: extreme humidity (90%)

Rick Phillips

[mouz59]

Make and model of DSLR: Canon EOS 40d
Make and model of scope: Takahashi FSQ 106 w/ Extender Q
Type, make and model of camera adapter: AP PFCT w/ Canon EOS t ring
Length of spacer needed to reach focus: none
Focal length of complete setup in mm: 850mm f/8
Measured distance between target and telescope in meters: ~16m
Evaluated resolution number:
Speed setting of camera: .3 sec
ISO: 100
Original picture format (RAW, JPG) and resolution (mpx) RAW 12mpx
Date and time: 07/11/2008
Weather conditions (sun and wind): N/A
Other pertinent information: shot in basement- cool, slightly humid, like all basements.

i also shot the ISO target. post those up in a bit.

the smaller chip made a BIG difference! - i'm still a little short, however of 12 mp, and it shows.

[dahyon]

All of the tests reported in this thread have ignored a fundamental parameter necessary for any meaningful interpretation of test chart results. The easiest way to explain is to refer to the 'Koren 2003' target because this has been explained in detail on Norman Koren's site; before his development of Imatest he used the sine pattern chart together with ImageJ (which can be obtained free from NIH web site) to plot the frequency response of his sine pattern. He clearly states that the 250mm chart should form an image of 5mm on the sensor. This is achieved by photographing from a distance of 50 focal lengths.

A simple equation shows the relationships between the variables:
F = (S/W)*D
Where:
F= Focal length
S = Width of object on Sensor
W = Width of Object.
D = Distance to Object

If the value of D is less than 50 focal lengths then a correction factor has to applied to allow for the change in magnification.

It is this parameter of magnification (S/W) intimately linked with distance D that is not being considered.

I used the Koren sine chart for a number of years testing my 35mm lenses on an istD DSLR before moving on to Imatest. The sine test chart is a good approximation to the newer slant edge analysis of spatial frequncy response where MTF is defined as the normalized magnitude of the Fourier Transform of the imaging system’s point spread function. Alternatively, the MTF of the sine pattern describes the attenuation of sinusoidal waveforms as a function of spatial frequency.

I am prepared to analyse a few complete 25cm sine pattern images (as original jpegs)in Imatest, if anyone would care to send them to me. The software is now quite smart and all that is required is an image of a complete sine pattern chart at full original size no cropping.

[JGobeil]

Dave,

Thanks for your comment about our test protocol. Your offer to evaluate some tests with Imatest is very kind and I am sure some will take advantage of it.

However, I think that the sine wave pattern that needs to form an image of 5mm on the sensor is not what we are looking for. Our test target does not use the the Koren target and we are only interested in finding the smallest distance between 2 lines that we can resolve. We also want to test for chromatic aberration, a very important factor for digiscoping. IMHO, if our test is flawed, all photographs that are not taken at a distance of 50 wave lengths must also be flawed... Your comment is correct if one is interested in making a scientific test of a lens to test all of its caracteristics, which is not the case for most of us.

Yes, one can analyse a lens using a software that costs more than a good scope and obtain scientifically correct results but we are only interested in doing a simple comparison between different digiscoping setups, using simple tools and without having to be a guru in optics. So far, testing has been done in this forum by posting photographs of birds - large and small - close and far away - colorful and grey... It is simply impossible to do a meaningful comparison this way. There must be a better way, somewhere between the Imatests and the "Look, my bird is sharper than yours". This is exactly what we are trying to accomplish. I don't think we are there yet but I think it can be done.

Once we have a decent tool to compare different digiscoping setups, we will have accomplished a lot. It should bring significant improvements in digiscoping and more enjoyment of this fine hobby, which has so far been the outcast, in French "parent pauvre", of bird photography.

If we all use the exact same test, we will be able to meaningfully compare the results. Yes, the test won't be scientific, the results won't be expressed in optic terms. Yes also, one will be able to evaluate his digiscoping setup and compare it to others - and it will be acccessible to all without cost.

[dahyon]

Hello Jules
Your test target is of course based on the ISO 12233 standard which requires that the active chart area (20cm 35.6cm) had to fill the full frame of the camera's ccd sensor using the framing arrows provided. The points I made still apply to your target. I have taken the liberty of analysing the 100% crops of 2 of the early targets just to illustrate the usefulness of Imatest. The resolution had to calculated in an unusual way because only cropped images were available.

You are obviously not aware of the earlier work I have produced on digiscoping resolution, no matter; I am intrigued by the high quality images from astro-scopes and am still willing to use Imatest of a full size image of your original ISO12233 copy which includes the 5 degree sloped squares which are there for the purpose of slant edge analysis. Thus you would obtain MTF values and CA giving you all the information you desire and some you are not aware of yet.

[Derry]

Dave, some interesting read here,, not much on math these days and age but will re-read a couple times and try to figure out your data,,

Derry

[JGobeil]

Dave, some interesting read here,, not much on math these days and age but will re-read a couple times and try to figure out your data,,

Derry

Impressive test Dave, but IMO too complicated for our needs. Unfortunately, I don't think we need nor want that sophistication.

Regards
Jules

[dahyon]

Jules
I can't simplify that output because I do not have the original files.

To illustrate: I have taken the ISO12233 image from the DPReview test of the Canon450D and analysed it with Imatest and present a simplified summary output showing change of resolution across the frame the change in chromatic aberration across the frame.

I have used the slant edge analysis method on all my digiscoping rigs the summary results of some have been placed in this forum some considerable time ago.

You have embarked on a scientific enterprise where standardisation and reliability are mandatory requirements.

[JGobeil]

You have embarked on a scientific enterprise where standardisation and reliability are mandatory requirements.

Sorry Dave but I don't agree with you. We ONLY want do see if a setup will be better than another one to take the picture of a bird at a distance. If one can resolve 20 on the target and the other one is limited to 15, then the first one will be doing a better job. That's all...

If people abide by the protocol, standardisation and reliability should be good enough for our purpose. There is nothing scientific about that. Our test should not be compared to Imatest or Koren in anyway. It will probably be an interesting leap forward for digiscoping compared to what has been done so far.

Of course there are people like you who will want to be more accurate and that are interested in scientific results. There are tools to do that, like you have demonstrated, but IMO they are unfortunately not for most of us.

Regards
Jules

[dahyon]

Good morning Jules
You are of course entitled to your opinion. Do others agree?

For myself I am only trying to help clarify some misunderstandings on test chart measurement. For instance the ISO chart 12233 being used in your protocol has a maximum resolution of 2000 lw/ph but the Canon 450D as shown in my previous post can resolve upto 2500 lw/ph. This explains in part why some of our digscoping group are passing the maximum on your protocol. The updated ISO 12233 chart being used by DPReview now has a maximum of 4000 lw/ph to cater for the latest generation of DSLRs. This kind of detail cannot be reached with a home printer.

For those who have tested the Koren sine pattern and apparently exceeded the 200 lp/mm think about this: A Canon 450D is 2848 pixels high and is 14.8mm high, the maximum the sensor can resolve is therefore 96 lp/mm. The discrepancy is due to the magnification factor as mentioned in my earlier post.

It is not my intention to browbeat anyone; I really want to know how good these astro-scopes are. If one of the contributors such as Derry sends me an original uncropped jpeg of the ISO12233 I will run Imatest for that individual, the data can remain private if they so choose.

[RJM]

Good morning Jules
You are of course entitled to your opinion. Do others agree?

I don't. But let them continue to delude themselves anyway.

Rick

[JGobeil]

Good morning Jules
You are of course entitled to your opinion. Do others agree?

For myself I am only trying to help clarify some misunderstandings on test chart measurement. For instance the ISO chart 12233 being used in your protocol has a maximum resolution of 2000 lw/ph but the Canon 450D as shown in my previous post can resolve upto 2500 lw/ph. This explains in part why some of our digscoping group are passing the maximum on your protocol. The updated ISO 12233 chart being used by DPReview now has a maximum of 4000 lw/ph to cater for the latest generation of DSLRs. This kind of detail cannot be reached with a home printer.

For those who have tested the Koren sine pattern and apparently exceeded the 200 lp/mm think about this: A Canon 450D is 2848 pixels high and is 14.8mm high, the maximum the sensor can resolve is therefore 96 lp/mm. The discrepancy is due to the magnification factor as mentioned in my earlier post.

It is not my intention to browbeat anyone; I really want to know how good these astro-scopes are. If one of the contributors such as Derry sends me an original uncropped jpeg of the ISO12233 I will run Imatest for that individual, the data can remain private if they so choose.

Thanks for the valuable info Dave. We know that the last version of the target and protocol is not correct. If it can stop raining :C I will do more tests. I think that, by testing at a fixed distance, let's say 25 meters, we won't exceed the maximum resolution of the target.

Regards
Jules

[Derry]

did two test today,,

1. camera - scope,,

2. camera - Olympus TC 1.4 - scope,,

upper right corner crop is from the original raw file,,


Make and model of DSLR: Olympus E3
Make and model of scope: Televue TV85
Make and model of converter or barlow: Olympus TC1.4
Type, make and model of camera adapter: Olympus 4/3 to T mount
Length of spacer needed to reach focus: 50mm
Focal length of complete setup in mm: 600mm ((840 with TC1.4))
.................................................. ...Camera has 2X crop factor (1200mm) ((1680 with TC1.4))
Distance to target: 10m ((14m with TC 1.4 ))
Speed setting of camera: 1/400 ((with TC 1.4 1/160))
ISO: 100 on all photos
Original picture format (RAW 10.7MP) to Jpeg 5.5MP
Date and time: 14th july 16:09 / 16:15
Weather conditions (sun and wind):sunny with clouds blowing through,, wind in the 5 knot area


----- camera ------------ corner crop ------------ camera with 1.4 ------- corner crop

[JGobeil]

I think that we will have to increase the distance in order to stop resolving at 20 max. Tomorrow, I will test 20-25-28-30m.

[Derry]

agree Jules,, if it is sunny here tomorrow I'll try the same distances with and without the 1.4 converter,,

Derry

[dahyon]

Good morning all
I now understand that some of you are striving to develop a qualitative test chart for relative comparison of astro-scopes.
I know that there has been a lot of time invested in developing the ISO 12233 chart here in this group but this chart was designed for scientific measurement and I suspect designed to make it difficult to reproduce at home.

Now if you want to develop a chart for qualitative comparison which can printed on a home printer then I suggest you have a look at this page:

http://www.clarkvision.com/imagedetail/relative-lens-sharpness

I have compared this method with Imatest and it works rather well for resolution. For relative comparisons you could just report the the value 8,6,4,3,2,1.

I have also been pondering about a qualitative test for chromatic aberration. One only has to photograph a black square on a white background to detect CA if present. With so many lens reviewers using Imatest there is a range of published images showing varying levels on chromatic aberration so it wouldn't take much effort to collate these to create a kind of strip chart showing the spectrum of CA. Thus it would be a simple matter of checking your own CA result with the pre-calibrated strip chart. Though I suspect the astro-scopes will have very little CA. In the mean time I will collate my own series of CA results an construct what will probably be the worst case scenario CA chart.

[Paul Corfield]

Dave, appreciate your continued input to this thread. The only problem I see with a chart like the one on the ClarkVision website in your last post is that the finest detail lines are right at the edge of the page. We are more interested in resolution at the centre of the lens so that chart would need to be chopped about a bit to be useful to us.

Although the current test isn't scientific and it wasn't meant to be, it does allow you form a simple visual interpretation such as sharpness, edge sharpness and CA. If there's something out there to satisfy a quick visual interpretation and anyone that wants to follow a more scientific approach then I'm sure we would all be happy to give it a try.

Paul.

[JGobeil]

Good morning all
I now understand that some of you are striving to develop a qualitative test chart for relative comparison of astro-scopes.
I know that there has been a lot of time invested in developing the ISO 12233 chart here in this group but this chart was designed for scientific measurement and I suspect designed to make it difficult to reproduce at home.

Now if you want to develop a chart for qualitative comparison which can printed on a home printer then I suggest you have a look at this page:

http://www.clarkvision.com/imagedetail/relative-lens-sharpness

I have compared this method with Imatest and it works rather well for resolution. For relative comparisons you could just report the the value 8,6,4,3,2,1.

I have also been pondering about a qualitative test for chromatic aberration. One only has to photograph a black square on a white background to detect CA if present. With so many lens reviewers using Imatest there is a range of published images showing varying levels on chromatic aberration so it wouldn't take much effort to collate these to create a kind of strip chart showing the spectrum of CA. Thus it would be a simple matter of checking your own CA result with the pre-calibrated strip chart. Though I suspect the astro-scopes will have very little CA. In the mean time I will collate my own series of CA results an construct what will probably be the worst case scenario CA chart.

Dave,

Thanks for the input and the link for this test.

I share Paul's opinion on this test and I don't think it would be more useful than ours once we find the sweet spot for the distance.

Regarding printing, I don't think it is a problem. With a simple Canon ink jet printer, I can easily print the Koren chart and resolve perfectly the maximum resolution of 200 lp/mm.

Regards
Jules

[dahyon]

Hello Paul
I use the ClarkVision chart in tandem with slant edge analysis, mainly because I find it more intuitive to visualise than abstract shapes. What I had in mind for you was this kind of chart (see attached - reduced for web) which tests the whole image frame both for resolution and for CA.
What do you think?

[JGobeil]

Hello Paul
I use the ClarkVision chart in tandem with slant edge analysis, mainly because I find it more intuitive to visualise than abstract shapes. What I had in mind for you was this kind of chart (see attached - reduced for web) which tests the whole image frame both for resolution and for CA.
What do you think?

Dave,

I see 2 difficulties with this testt - it is still scientific and requires math calculation behond the reach of many. Reading the Clarkvision site, it looks somewhat similar to the Imatest but less sophisticated and it doesn't require software to analyse the chart.

Like you said it so well, we are trying to achieve a QUALITATIVE test. Even if I can understand those calculations if I make the effort, I don't really have an interest in optics nor the in depth knowledge to understand the full meaning of the results. All I want is a simple number that will reasonably describe the resolution of a given digiscoping setup and that will make comparison possible.

Second, focusing on it may be quite difficult at 50 ft. Unfortunately, we don't have access to a full resolution file to print and test it.

I have tested our target derived from the ISO one yesterday at 20-25-30 meters and found it difficult to focus accurately. Results below - the mm value includes a 1.6 sensor crop factor.

2 findings from these tests:

1- The more magnification, the easier it is to focus.
2- The maximum resolution value increases with magnification, which does not make sense for our tests :C

IMO, this clearly demonstrates that our initial parameter of using a distance that will fill the width of the sensor completely with the target is the way to go. This is also a parameter of the Clark test.

In order to achieve what we are trying to do, we will need a target that is not as easy to resolve as our version of the ISO chart. The maximum resolution number should be impossible to reach. Unfortunately, it may be difficult to print.

Opinions please !

[Paul Corfield]

As it's feather detail we are trying to resolve why not have a black box of a set dimension on the chart and stick a feather to it, not to exceed the edges of the box. The detail on a feather is much finer than we can print. To make the chart easier to focus on we could have some bigger, bolder black areas that are easier to see in the viewfinder. Just some random thoughts.

Paul.

[JGobeil]

As it's feather detail we are trying to resolve why not have a black box of a set dimension on the chart and stick a feather to it, not to exceed the edges of the box. The detail on a feather is much finer than we can print. To make the chart easier to focus on we could have some bigger, bolder black areas that are easier to see in the viewfinder. Just some random thoughts.

Paul.

Neat idea Paul. However, I don't know how we would measure the resolution unless we ask a bird !

I'll try to do another target, starting from the Original ISO and making the resolution lines smaller. I'll post it for an opinion.

[Derry]

Paul you shot that feather from five feet so that is not a valid test,,:t:

Jules, I also did the test at the 20/25/30 and will be posting them today,, working on some of the granddaughters birthday party at present, you know about those priorities,, scope test work falls to the rear of the pack,,

do agree the focusing is something else at those distances,, really can see the need for a feather touch focuser,, even my study tripod would not hold the chart still at 10X live view trying to focus,, need a sturdy work bench to mount it all on,,

Derry

[Paul Corfield]

Paul you shot that feather from five feet so that is not a valid test,,:t:

Derry

LOL, that was from 10m with the 2X barlow. Here's the 100% crop. Just thought it would add to the visual aspect to the test rather than something to actually measure.

Paul.

[JGobeil]

Here is a tentative for V. 3.0 of the target.

It is similar to V. 2.0 except that I have reduced the vertical of the resolution lines set by 15%. I have kept the horizontal at 100%. I have used this new set to make the diagonal lines sets. It was more complicated for the lines set at the bottom - for those I have reduced both the horizontal and the vertical by 15% - not exact but close enough.

This is the best I can print with my Canon i960. My printer is unable to resolve if I reduce by 20%.

I have tested it full frame without a TC and with a 1.4 TC. In both cases, I can resolve at 20 maximum, but not much margin left.

You can get the file here:
http://julesgobeil.com/private/digiscoping%20target%20v3_0.jpg

Please try it and let me know what you think.

Regards
Jules

[Derry]

new chart looks good and agree we need to fill the frame and go with that reading,,

I have posted my findings below at 20,25 & 30m,,

at 200% on the original the finest line I can see clearly is..

20m = 16/17 on the angles and 16 on the hortizontal

25m = 15 on the angles and 14 on the horizontal

30m = 12/13 on the angle and 11 on the horizontal

was a warm, partly cloudy and windy day,,

Derry

[JGobeil]

Good work Derry. Don't forget that it is NOT "the finest line I can see clearly" but the highest number where you can see white spaces BETWEEN ALL FIVE LINES.

Testing it this way, I suspect your results will be close to mine.

I'm happy that you also consider that filling the frame is the way to go.

Regards
Jules

[Paul Corfield]

I think the anti aliasing is really starting to suffer in the new test image, especially when compared to the original ISO 12233 chart. Is there a way to keep the original quality of the ISO 12233 chart even after repeated alterations?

I tried to print the new one but the jaggies are quite apparent.

Paul.

[JGobeil]

I think the anti aliasing is really starting to suffer in the new test image, especially when compared to the original ISO 12233 chart. Is there a way to keep the original quality of the ISO 12233 chart even after repeated alterations?

I tried to print the new one but the jaggies are quite apparent.

Paul.

Humm... I don't seem to have that problem here - maybe I posted the wrong file. Let me see but it won't be until tonight.

[Derry]

my printed test chart (new one) is not as good on the line edges as the last one,, I'm still using the same paper,,



Jules, the lines I could see on the 20-25-30m photos are what I can count on my HD monitor viewing at 200%, 300% started distorting them,,

I sent David (dahyon) one of my first ISO photos to run his Imatest software on and he sent back several graphs and information on how well the Televue scope and Oly E3 did,, was nice to see some data on my set-up and how it compares to an original standard,, thanks David,,

Derry

" late edit,, was just looking at the chart at 100% in photoshop and it looks fine with all smooth edge lines but still does not print as well as the original charts,,"

[JGobeil]

Here is a new target. I have done it using the original ISO 12233. Resolution at 20 maximum is as small as I can resolve very clearly with my printer. Paul and Derry, please try it and let me know what you think - unfortunately I cannot try it, it is raining again...

Other minor changes:
Resolution lines in all 4 corners
Size now 10" x 6.667" (254 x 169,33 mm) to give it a 4/3 (36x24) ratio.

Regards
Jules

http://julesgobeil.com/private/digiscoping%20target%20v3_1.jpg

[Derry]

Jules looks pretty good,,

I still need to go to Staples and pick up some better paper,, will do today and try a test shot before the sun goes down,, is 35.6C here today so will wait till it cools a tad,, humidity feels like 90%,, looks like the trees are even sweating,,


EDIT,, have the very good paper now and the chart will only print with smooth lines if printed in the good setting and in color on my printer,, tried several settings in B&W and ended up with jagged lines,, noticed the one I mentioned above was printed in the color setting,,????? the color printed is a dark purple (I'm a tad color blind though) but the 20 lines are resolved very good,,


Derry

[JGobeil]

Jules looks pretty good,,

I still need to go to Staples and pick up some better paper,, will do today and try a test shot before the sun goes down,, is 35.6C here today so will wait till it cools a tad,, humidity feels like 90%,, looks like the trees are even sweating,,


EDIT,, have the very good paper now and the chart will only print with smooth lines if printed in the good setting and in color on my printer,, tried several settings in B&W and ended up with jagged lines,, noticed the one I mentioned above was printed in the color setting,,????? the color printed is a dark purple (I'm a tad color blind though) but the 20 lines are resolved very good,,


Derry

The chart is in B/W. Yes you must print in the best setting and you must also tell the printer you have hi-res paper.

[Derry]

Jules,, tried a few more printer settings with various photo software and when best is used the lines remain jagged out of my HP 970 CXI,, agree ya would think best should be cleaner and clearer than normal,,

did select the new HP paper I purchased,, doubt if the purple color will hurt as the 20 lines are well resolved and will give it a try,,

sent ya a PM,,

Derry

[JGobeil]

Jules,, tried a few more printer settings with various photo software and when best is used the lines remain jagged out of my HP 970 CXI,, agree ya would think best should be cleaner and clearer than normal,,

did select the new HP paper I purchased,, doubt if the purple color will hurt as the 20 lines are well resolved and will give it a try,,

sent ya a PM,,

Derry

Humm... you made me nervous. Just to make sure, I downloaded the file off the Net and printed it. It prints very sharp in pure B/W. Something must be wrong with your print settings. Unfortunately, I don't know anything about HP printers. Maybe someone else can help you.

[Paul Corfield]

I must admit I'm still having trouble with the chart too and I think it's still an issue with loss in detail compared to the original chart. I did a comparison by enlarging both charts. The image on the left is our chart and the image on the right is the original ISO 12233 chart. Our chart should look like the original and it should be possible if we work in a lossless format. I'm having to work on a painting deadline at the minute otherwise I could have a go myself but I should have some time later next week.

Paul.

[JGobeil]

I must admit I'm still having trouble with the chart too and I think it's still an issue with loss in detail compared to the original chart. I did a comparison by enlarging both charts. The image on the left is our chart and the image on the right is the original ISO 12233 chart. Our chart should look like the original and it should be possible if we work in a lossless format. I'm having to work on a painting deadline at the minute otherwise I could have a go myself but I should have some time later next week.

Paul.

Paul,

When I open the original I have and crop the "20 max" lines like you do, it does not come as sharp as your copy - see below. Is your file named: ISO_12233-reschart.pdf and what parameters do you use to open it ?

[Paul Corfield]

The only way I have found so far to get the lines to come out as clear as the image I posted was to open the PDF in Adobe Reader and then I zoomed to 3200% and did a screen grab. That's not a practical way though to make a whole chart so I wonder if there is a way to convert the pdf to a format that wont lose the detail that is there. The detail is obviously present in the original to be able to zoom that much so it all gets lost in the conversion.

Paul.

[Derry]

Jules, could you e-mail us your original file that is not in the PDF format,,??

Derry

[JGobeil]

Made some tests this afternoon with the target. I tried saving the lossless original (.TIF) to other lossless formats - .PNG and .PDF and is was no better that the .JPG available from my Web Site.

I also tried to make a new target using vectors in Corel Draw. This turns out better on the screen but the print is no better or worse than the last .JPG that I supplied.

I took a very quick macro picture of the V. 3.1 target, as printed with my Canon inkjet. Hanheld at 6". As you can see, 20 is easily resolved. I'm afraid it is the best I can do !

IMO, the limitation is with the printers and the monitors. If you crop at 500%, the lines become almost perfect. Comments and suggestions please !

[Paul Corfield]

I think I've found a solution. On the link below is a basic Imatest chart and it's in SVG format. It has all the parts we need and can be edited with an SVG editor to form your own chart. There's also a link for a free SVG editor which I've been playing around with this morning. It should be pretty simple to come up with a new chart similar to what we have now and be in the highest quality possible.

To give everyone a fair chance at printing it should be made available in SVG format and say a TIFF format but not jpeg. With the free SVG editor there's no reason for anyone not being able to print at the highest quality possible on their printer an if needs be they can just use the TIFF.

Link with charts and useful info on editing, printing etc. http://www.imatest.com/docs/testcharts_SFR_SVG.html

Chart is here http://www.imatest.com/docs/images/small_chart_contrast_20.svg

Free SVG editor http://www.inkscape.org/

They have the SVG file available as a PDF too and it's loads bigger than the ISO12233 chart. I opened it in Photoshop at something like 1200 dpi and it came up very good, way better the the ISO12233 one, not as perfect as the SVG though.

Paul.

[JGobeil]

Great Paul - I'll be working on it. I should be able to find time today or at the latest tomorrow.

Lots of thanks !
Jules

[JGobeil]

I think I've found a solution. On the link below is a basic Imatest chart and it's in SVG format. It has all the parts we need and can be edited with an SVG editor to form your own chart. There's also a link for a free SVG editor which I've been playing around with this morning. It should be pretty simple to come up with a new chart similar to what we have now and be in the highest quality possible.

To give everyone a fair chance at printing it should be made available in SVG format and say a TIFF format but not jpeg. With the free SVG editor there's no reason for anyone not being able to print at the highest quality possible on their printer an if needs be they can just use the TIFF.

Link with charts and useful info on editing, printing etc. http://www.imatest.com/docs/testcharts_SFR_SVG.html

Chart is here http://www.imatest.com/docs/images/small_chart_contrast_20.svg

Free SVG editor http://www.inkscape.org/

They have the SVG file available as a PDF too and it's loads bigger than the ISO12233 chart. I opened it in Photoshop at something like 1200 dpi and it came up very good, way better the the ISO12233 one, not as perfect as the SVG though.

Paul.

Paul,

Spent quite a bit of time testing this solution and I can't get it to work well.

It's fine on the monitor but does not print well. The JPEGs I have supplied are as good if not better under the loupe.

Another problem with Inkscape is that it is difficult to get it to print all objects. There seems to be a bug in the printing routine. Making a target like our V. 3 is easy, getting it to print is a nightmare...

Have you been able to print the chart ? Can you resolve the 20 size on the print ?

[Paul Corfield]

Because I need to finish a painting for this Friday I haven't been able to devote any time to this so it's going to be next week before I can have a look. I'm away at a wedding over the weekend too. It's a shame as the weather is great here at the moment and I can't get out with the scope. :-C

Paul.

[Derry]

same issues here,, Vist on the new HP would not allow the SVC file to be saved,, tried on the wifes laptop and saved but the output is not good,,

Derry

[JGobeil]

No... this project is not dead. Paul and I have been quite busy lately. We are presently working by email to come up with a new target, hopefully the last one. We will also propose a formula to calculate the "Effective Resolution" of a digiscoping setup to compare different setups and configurations in terms of resolution.

[phaser]

Make and model of DSLR: Pentax k20d
Make and model of scope: Celestron C5
Type, make and model of camera adapter: T-Ring with celestron T-adapter
Length of spacer needed to reach focus: T-adapter 2"
Focal length of complete setup in mm: i'm not sure. celestron page say's 1250mm (1850mm with 1,5crop factor)
Measured distance between target and telescope in meters: 20m
Evaluated resolution number:
Speed setting of camera: 1/10 sec
ISO: 100 (Should use higher iso but forgot)
Original picture format (RAW, JPG) and resolution (mpx) RAW 14,6mp
Date and time: 15th august 18.20
Weather conditions (sun and wind): Shade, slight breez.
Other pertinent information: target 19x24cm bad printout on copy paper


can anyone tell me the focal lenght with my setup?
http://www.celestron.com/c2/product.php?CatID=30&ProdID=207#specs