Tord
Well-known member
Daniel,
How much work was it adding ball bearings, and what tools are needed to perform the surgery? Could you share a pointer to what ball bearings you used?
-
Welcome to BirdForum, the internet's largest birding community with thousands of members from all over the world. The forums are dedicated to wild birds, birding, binoculars and equipment and all that goes with it.
Please register for an account to take part in the discussions in the forum, post your pictures in the gallery and more.
Astroscope + DSLR = Setups! (1 Viewer)
- Thread starter cango
- Start date
How much work was it adding ball bearings, and what tools are needed to perform the surgery? Could you share a pointer to what ball bearings you used?
DanC.Licks
AKA Daniel Bradley
It was not super easy and took some puttering, but it is also not rocket science. If I had an 18mm reamer it would have been much easier. As is, I hand to ream out the holes to just over 18mm using tapered reamers I use in my musical instrument work, and cast them in epoxy to exactly 18mm using a brass form I turned on my mini lathe. The bearings (12x18x4) are cheap. Got them on ebay from Kugellager-Handloser. Cost about €2.70 a piece and €1.80 for shipping, (12,60 for four). The shafts are also .2mm undersized, 11.8 rather than 12mm, and the grove between the plain part of the shaft and the thread has to be filled out to make the smooth part about 4mm longer. This I also did with epoxy. So it was a lot of playing around, but hey, I'm retired!o
If you want I could take some pictures. Now that I know how to do it it might be easier if I did it for you. Mail me.
If you want I could take some pictures. Now that I know how to do it it might be easier if I did it for you. Mail me.
I'm not sure if that is right. I'm not saying i disagree, as you know your stuff. You have more experience with your scope than I do with mine.
On camera lenses imaging test software like imatest always show that a bit of stopping down improves the sharpness of the image. (see SLRGear.com tests for example) Most lenses are about f2 to f4. Even the f1.8 lenses really hit their best at about f4-f5.6 . The f4-f5.6 lenses are usually best at f8.
This may be different in scopes as they are highly optimized for infinity. Unfortunately they are also designed for spherical eyeballs which means field flatness of the focus plane is not very good. My guess would be that stopping down improves the typical lens aberrations wide open as well as the field flatness. I have no data to back that up.
To my eye with baffle shows a lot of improvement over most of the frame. The first image is really only useful at the center. The rest is starting to smear. On the 3rd image the center 2/3rds seem useful.
Is that a crop sensor or full frame?
DanC.Licks
AKA Daniel Bradley
Good astro scopes have to be made to achieve top sharpness wide open. They are seldom stopped down, although my old SW had the two part lens cap for just that purpose. The astro photographers use field flatteners to make sure that the stars on the edges of the frames are round. Has to do with projecting the image on a flat surface. I think most camera lenses have flatteners built right into them. Scopes do not because they are not always necessary and they are expensive. We don't need them at all for birds, especially if we use crop sensors.
I noticed a little improved sharpness with my old Skywatcher ED doublet stopped down, but it was more due to improved contrast and DoF. I didn't really notice a huge difference in the resolution. (I use an ISO 12233 resolution chart for tests.) I haven't tested my new 90/600 ED triplet as thoroughly as it shown none of the shortcomings wide open that the SW had. I will do so, and report back if I see any big difference in resolution.
In the old SLR days, bright lenses were used most of the time wide open to make it easier to focus and to frame, but then were automatically stopped down. Shooting them wide open was never really very good, and we knew it and put up with it.
I noticed a little improved sharpness with my old Skywatcher ED doublet stopped down, but it was more due to improved contrast and DoF. I didn't really notice a huge difference in the resolution. (I use an ISO 12233 resolution chart for tests.) I haven't tested my new 90/600 ED triplet as thoroughly as it shown none of the shortcomings wide open that the SW had. I will do so, and report back if I see any big difference in resolution.
In the old SLR days, bright lenses were used most of the time wide open to make it easier to focus and to frame, but then were automatically stopped down. Shooting them wide open was never really very good, and we knew it and put up with it.
Miles Green
Active member
Hello! Reading the latest posts i thought i'd chime in with some info on my TS 500/80 super apo. As i mentionned earlier in this thread, i inserted a baffle with drastically increased contrast. I've also been experimenting with stopping down the lens by about a stop. There is a noticeable but not significant sharpness increase when i use it for near subjects (close to min focus about 6 meters away). There is no difference further away, on the contrary maybe. There is however a slight focus shift - meaning i have to re-adjust focus a little as i stop down - which is not very practical at all. Basically it's fine in live-view, but that's about it. To be honest i don't know of any fast lens that doesn't benefit even a little upon stopping down, so i'd say this is normal. Anyway, here is a pic of my cat, full res of course. Finally, i'm about to get an eyepiece for my telescope (and a star diagonal). I think it's going to be a TV Delos 12mm. What do you think?
My cat
My cat
Last edited:
All I get at the link is XML
This XML file does not appear to have any style information associated with it. The document tree is shown below.
<Error><Code>AccessDenied</Code><Message>Request has expired</Message><RequestId>6D86BC82D5E85D74</RequestId><Expires>2013-10-12T22:12:14Z</Expires><HostId>KtVigJJCZhi7mpiOC9I6aW9NAgb8CIHE5yhJQF8C0EYvlai57RzWs6Qee2aQzjkO</HostId><ServerTime>2013-10-13T02:25:38Z</ServerTime></Error>
Miles Green
Active member
I think i fixed the link now, thanks!
Tord
Well-known member
Miles,
The close up of your cat shows an incredible level of detail rendering.
I am curious about results you have obtained in the field, do you have a pointer to e.g. a gallery with pictures taken using the TS 500/80 super apo?
Tord
Well-known member
Ts102 + E5
The past days I have been using a newly acquired E5 body on my TS102/700 scope and was quite surprised how well the setup performed. I was hesitating at start due to the weight of the body (close to 1kg with batteries and strap) however this load was easily handled by the focuser, 3" "improved Crayford", even fully retracted. On the lensmaster GH2 gimbal head the setup is a pleasure to operate, even though the scope alone weighs 5+ kg.
Also I was surprised how clear the image in the optical viewfinder was, much easier to focus than when using the E620 on the Skywatcher. (F/6.8 vs F/7.5 and size of viewfinder both contribute in this).
I also think the keeper rate on BIF is exceeding the one with the E-M5, but I need more samples to conclude on this.
Still, I miss the E-M5 stabilized EVF and EVF magnification for static objects.
The past days I have been using a newly acquired E5 body on my TS102/700 scope and was quite surprised how well the setup performed. I was hesitating at start due to the weight of the body (close to 1kg with batteries and strap) however this load was easily handled by the focuser, 3" "improved Crayford", even fully retracted. On the lensmaster GH2 gimbal head the setup is a pleasure to operate, even though the scope alone weighs 5+ kg.
Also I was surprised how clear the image in the optical viewfinder was, much easier to focus than when using the E620 on the Skywatcher. (F/6.8 vs F/7.5 and size of viewfinder both contribute in this).
I also think the keeper rate on BIF is exceeding the one with the E-M5, but I need more samples to conclude on this.
Still, I miss the E-M5 stabilized EVF and EVF magnification for static objects.
Keep in mind the Dawes limit which says angular resolution of a lens is a function of the size of the lens. For small birds in the distance the challenge is clearly resolving the tiny details. If you find your images have detail at 1080P size but turn to mush at large 12-36MP sensor size look at the size of your lens which gets very expensive very fast in refractors.
The formula takes different forms depending on the units.
R = 4.56/D D in inches, R in arcseconds
R = 11.6/D D in centimeters, R in arcseconds
where D is the diameter of the main lens (aperture)
R is the resolving power of the instrument
http://en.wikipedia.org/wiki/Dawes_limit
Now a 1 inch object at 100 yards is 1 minute of arc.
An 80mm lens that is perfect can resolve 1.45 seconds of arc
an 8" mirror that is perfect can resolve 0.57 seconds of arc
A 10" mirror that is perfect can resolve 0.456 seconds of arc
Only you know if your system is giving you the detail you are looking for.
The formula takes different forms depending on the units.
R = 4.56/D D in inches, R in arcseconds
R = 11.6/D D in centimeters, R in arcseconds
where D is the diameter of the main lens (aperture)
R is the resolving power of the instrument
http://en.wikipedia.org/wiki/Dawes_limit
Now a 1 inch object at 100 yards is 1 minute of arc.
An 80mm lens that is perfect can resolve 1.45 seconds of arc
an 8" mirror that is perfect can resolve 0.57 seconds of arc
A 10" mirror that is perfect can resolve 0.456 seconds of arc
Only you know if your system is giving you the detail you are looking for.
janvangastel
Well-known member
Interesting. My 80 mm diameter Swarovsky can resolve 1.45" details (ideally). That's an object of 0.73 mm at 100 meters distance. The human eye can resolve - ideally - 1' or 60", but less ideally, let's say 90". So for a human eye to be able to see the 0.73 mm object (or detail within a larger object) at this distance, it should be magnified 90/1.45 = 62x. An object or detail within an object, the size of the thickness of human hair (say 100 micrometer or 0.1 mm) can (if my reasoning is correct) be seen with the same setup at a distance of 0.1/0.73*100 meters = 13.8 meters.
Last edited:
JGobeil
Nature Photographer
Humm... this is what the theory says but I find that those formulas are not very useful in the field and don't have much meaning.
There are many factors that challenge those formulas in real life: quality and amount of light available, wind, heat waves, haze, etc.
Case in point, look at the 2 photos below. Both subjects were about 200-250 meters away and the equipment was the same (EM-5 and SW80ED with 1.5X TN).
The first one of the Gulls was taken Tuesday on a nice cool, sunny, crisp and windless Automn day. ISO 400, 1/1000 s.
The second one of a juvenile Black Guillemot was taken last weekend on a cloudy day shortly after sunrise when the light was low and bland. ISO 1600, 1/1000 s.
Both are substantial crops and were processed in Lightroom to make them as nice as possible.
They are not great shots but I think they show the difference between good and bad conditions. They illustrate well that real life and theory often differ a lot.
Regards
Jules
Attachments
Tord
Well-known member
I think Dawes limit is still useful to understand what resolution an optical device is capable of delivering, best case, disregarding from the distortions through air.
Close range pictures, say 10 meters, should reveal details with a size of 0,07 mm. This would correspond to the textures in feathering or the finest details in in a 300DPI print on high quality paper.
Close range pictures, say 10 meters, should reveal details with a size of 0,07 mm. This would correspond to the textures in feathering or the finest details in in a 300DPI print on high quality paper.
JGobeil
Nature Photographer
Tord,
Don't you think most telephoto lenses can resolve that level of details under good conditions ?
Tord
Well-known member
If you refer to the consumer grade lenses, something like 300mm F/6.3 then no, this would be against the laws of physics. High grade lenses something like 300mm F/4 or F/2.8 are probably capable - but then you need to come twice as close to preserve the details on sensor. Or use 2X TC.
A 150mm front lens would render twice the resolution, but such a scope would be a beast and heavy.
A 150mm front lens would render twice the resolution, but such a scope would be a beast and heavy.
DanC.Licks
AKA Daniel Bradley
This would be getting there
http://www.the-digital-picture.com/Reviews/Canon-EF-1200mm-f-5.6-L-USM-Lens-Review.aspx
Our two worst enemies are thick air and bad light. That said, a better lens is still going to perform better in the same bad conditions as a not so good one. I have noticed a big difference between the SW 80/600 and my new triplet 90/600 in such conditions, and it has little (if anything) to do with the slightly better Dawes value. It has to do with better contrast and nearly a total lack of CA. They are still crappy pictures, but a little less crappy.
http://www.the-digital-picture.com/Reviews/Canon-EF-1200mm-f-5.6-L-USM-Lens-Review.aspx
Our two worst enemies are thick air and bad light. That said, a better lens is still going to perform better in the same bad conditions as a not so good one. I have noticed a big difference between the SW 80/600 and my new triplet 90/600 in such conditions, and it has little (if anything) to do with the slightly better Dawes value. It has to do with better contrast and nearly a total lack of CA. They are still crappy pictures, but a little less crappy.
Tord
Well-known member
The Dawe's value gives the maximum resolution possible to render in ideal conditions. In practice there are many hurdles that may degrade the resolution, such as bad air/distortions, poor light/poor contrast/noise.
When upgrading to the triplet TS102, what struck me was not that sharpness or resolution were much higher (they are a bit), it was the higher contrast and lack of CA, which should result in better pictures due to less "color bleeding". I also immediately noted there is no more purple color visible in the brightest sun reflections.
This 1200mm / F5.6 Canon lens has a front lens with a 214mm diameter, a beast indeed.
At a weight of 16.5kg, my SW80 feels like a mosquito, and my TS102 feels like a feather (slight overstatement, but my gear is portable, the 1200 is not).
The person who tested it remarked it was difficult to frame and track subjects with a FF camera sensor. We are doing this with quite some ease (at least I don't find it difficult) with our 600-700mm scopes fitted with APSC or 4/3 sensor (angle of view comparable). It comes with practice.
Also I noted HE remarked about the lens taking advantage of stopping down from sharpness point of view, as well as CA being present mid way to the corners.
$ 120k for two EV stop advantage (potentially one stop only if the lens is meant to be stopped down) and for AF that is SOMEWHAT prone to hunt... Hmm...
But it would be interesting to borrow one and test against our scopes, and I respect what Canon engineers have managed to design and deliver.
JGobeil
Nature Photographer
I would'nt even consider that big Cannon without a built-in caddy...
I'm surprised that you consider that the SW80ED generates CA - I find that mine is quite immune from that and when it shows some, it is very light. I'm more worried by low contrast and narrow DOF.
IMO, CA is not that big a problem these days since it easy to correct in post processing, as long as it is not too severe. Lack of contrast can also be corrected quite well in PP, but I suspect that some of the resolution is lost for good.
Last edited:
DanC.Licks
AKA Daniel Bradley
There were many times where the SW showed no obvious CA at all, but it did with high contrast or back lit subjects, like BiF. The problem is that CA can reduce contrast and resolution by spreading the light around, even at times when it is not obviously visible. True, you can get rid of CA (fringing) in PP, but that seems to simply take the color out of a magenta or cyan fringe. Better not to have it there in the first place.
DoF is a fact of life with long lenses. The only way to improve it is to stop down, which is seldom an option.
DoF is a fact of life with long lenses. The only way to improve it is to stop down, which is seldom an option.
