Some digiscoping experiments with a dslr (1 Viewer)

[Paul Corfield]

The VR-1 filter is worth getting and does work very well from test photos I've seen. I've attached a photo below from the Cloudy Nights astronomy website. There's a couple more photos on the link below also along with a price for the 2" version. They used to make a 1.25" version but I'm not sure if they still do. On my scope I'd just remove the 2" eyepiece holder and screw it into that. It's most likely going to be my next purchase as like all achromat telescope I suffer with some fringing in bright light. I remove it in Photoshop but it's a pain when you have to do it wth every photo.

I tried the Baader Semi Apo filter a few weeks ago. It's also a minus violet filter and a contrast booster all rolled into one. The coating was quite dark though and the shutter speeds went down considerably. Apart from that it did a good job of removing the aberration. The William Optics filter is much better, light transmission is over 80% and blue/violet fringe removal is around 90% according to what I've read. There's a slight color shift but that can be removed by setting the manual white balance on the camera.

http://www.opticsplanet.net/william-optics-2-vr1-violet-reducer-filter-wa-vr1-2.html

Paul.

 

[JGobeil]

I'm getting there...

My venture into digiscoping has been an exercise in frustration so far. The best I had been able to do was with a Nikon P5100. Even then, I was not satisfied with my results, not because the camera is not good but because I had to rely on the LCD monitor to focus. I wear progressive glasses or no glasses when using a viewfinder and I find that accurate focusing with the LCD is just about impossible because it doesn't have a dioptric adjustment. IMO, I need a good viewfinder in order to have good results.

I then tried prime focus with nothing but a tele-converter between the DSLR and the scope - I tried it with varied extensions fore and aft and the setup would not focus further than about 3 meters. Arrchhh !

Then I tried it with a 50mm lens and an eyepiece. Bingo ! I think I've got it...

Here is my setup:
Canon 20D DSLR
Canon EF 50mm f/1.8 Mk I lens (the original one with metal mount)
52-43mm step-down ring
Baader Hyperion 21mm eyepiece
Pentax PF-80ED scope

This gives me about 40X. The first tests look promising. Attached are 2 examples, shot at about 20-25 meters. I am sure I can do much better; it was very cold and I only took a few shots without the remote trigger, focusing very fast.

I still have to find a way to get the metering to work and I'll be in business. What do you think ?

 

[Neil]

This gives me about 40X. The first tests look promising. Attached are 2 examples, shot at about 20-25 meters. I am sure I can do much better; it was very cold and I only took a few shots without the remote trigger, focusing very fast.

I still have to find a way to get the metering to work and I'll be in business. What do you think ?[/QUOTE]

Looks promising Jules. I wouldn't worry about the metering. I usually use Manual Metering anyway for 50% of my images. Neil.

 

[Paul Corfield]

Very good Jules.

Something else you can try is maybe use your teleconverter with a lower power lens. If I use my 28mm lens with a 2X teleconverter I get sharper photos than if I use my 55mm Takumar lens through a lower power eyepiece (24mm DCL28) that gives similar magnification. The 28mm lens on it's own produces a very bright image but quite a bit of barrel distortion through an eyepiece. With the 2X teleconverter the distortion is removed. Also play around with the F stop numbers. An F1.8 lens will probably produce it's sharpest photos at around F4-F5.6 and it wont affect shutter speed hardly at all on the scope. You could even try the 2X teleconverter with your current setup for extra high power. Don't worry about the metering as I doubt it will work reliably on the scope and after a while you just get a feel for the shutter speeds anyway.

Here's a photo of the moon I took on the 16th Feb this year. Taken with my Samsung GX-1L DSLR fitted with a 28mm lens and 2X 7 element Tamron F-System teleconverter through a 17mm Baader Hyperion EP and using shutter release cable.

Paul.

 

[JGobeil]

Thanks Neil and Paul for your comments. Very nice picture of the moon Paul.

I haven't found a way to get the metering to work but it doesn't worry me too much. It will be like in the old days where my first 35mm viewfinder camera didn't even have a meter. I was a student then and I paid 15$ for it...

My tele-converter is a Canon and will not fit behind the 50mm lens unfortunately. If I invest more in this setup, it will probably be for Hyperion 13mm eyepiece that would give me 61X.

I'll keep you posted on my progress.

 

[Paul Corfield]

The only thing I'd be very wary of is that the amount of light lost with a 13mm eyepiece would be quite a lot. My 17mm Hyperion with a 50mm lens is barely usable in dull weather but not too bad if it's sunny. In astronomy, by swapping an eyepiece for one of double the power results in just a quarter of the light or in other words the light goes down by a factor of 4. It's not all that noticeable to the human eye in daylight viewing but it is very noticeable to a camera.

For more power from the same set up I'd try getting some extension tubes to mount between the camera and lens. You don't lose all that much light and the gains are big. I find that 80mm of extension tubes will double my magnification with very little loss in detail and not much loss in light. Plus you can use various length tubes to vary the magnification from a single eyepiece. The only trade off is it makes the distance from camera to scope a little longer but I never leave the camera on the scope as I mentioned in an earlier post.

Paul.

 

[Trinie]

Hi Jgobeil,

Both pictures look quite good. Happy to hear you have it going in the right direction now.

Can you post a few pics of how your set-up looks with a 50mm lens? Can you focus with the 50mm and will this set work with zoom eye pieces.

 

[erniehatt]

Well done Jules, it,s looking good. Ernie

 

[Kuldoode]

Fairly new to all this digiscoping etc

hi All,

i have a Nikon coolpix 885 camera and an acuter 20-60 80mm scope. I am planing on losing my camera shortly in place of a Nikon D40.

Can anyone comment on the Nikon D40 ?, i know its only an entry level DSLR camera, but hey we all got to start somehwere and at £279 it suits my pocket. ?

The camera comes with an 18-55mm lens, can someone explain to me how the magnification factor works on this. I was thinking on buying at 50 - 300mm lens as well but i dont know what this related to in multiplication factors. can someone help.

Regards

Andy

 

[Paul Corfield]

Don't know much about the D40 but I thinks it's an ok camera from the bits I've read in the past. The crop factor is 1.5X so just multiply any lens by 1.5 to get the 35mm lens equivalent. So a 50mm - 300mm would become 75mm - 450mm

Paul.

 

[Kuldoode]

So whats that is x factor, 75mm being x ?? and 300 being x ??

 

[Paul Corfield]

As a rough guide (depending on the point and shoot model) 10X magnification is in the region of a 350mm - 380mm lens on a 35mm SLR. So 75mm would be around 2X and 450mm would be around 12X

If you want good detailed photos with just a DSLR and a lens then you need to be getting fairly close to the subject depending on it's size of course.

For loads of power then stick with digiscoping and for somewhere in between do what I do and mount the dslr body to an astro style scope and shoot prime focus or with a teleconverter/barlow configuration. My set up gives me 40X - 80X magnification with the teleconverter + extension tubes and around 20X when used prime focus (480mm equivalent).

Paul.

 

[Kuldoode]

Am i right in saying its a samsung you have ? does it have the motor on it for focusing lens, i have just noticed the D40 does not. The motor on the D40 are actually in the lens itself.

Could you give me a parts list , cost of what you use for your 40 - 80x as i am impressed with the pictures you have taken up to now.

I have an acuter scope 20-60x @ 80mm.

regards

 

[Paul Corfield]

I think with most dslr's the motor will be in the lens, it is with my Samsung and also my dad's Canon 400D.

I only went for my Samsung because it was cheap (£180 second hand on ebay). I'm sure the better known makes would out perform mine by a fair margin.

For the scope you would need to be looking at a good 80mm ED achromat or a fluorite apo. Expect to pay around £400 for an achromat and £500 upwards for an apo. Apo's remove nearly all aberrations so they are the better choice.

My scope is a 480mm F6. The longer the focal length then the more magnification.

Teleconverters etc are cheap on ebay, I get mine averaging around £10

Paul.

 

[JGobeil]

As a rough guide (depending on the point and shoot model) 10X magnification is in the region of a 350mm - 380mm lens on a 35mm SLR. So 75mm would be around 2X and 450mm would be around 12X

Paul.

Paul, I think that the formula is x = mm/52 since a 52mm lens produces no magnification on a 35mm camera, so a 150mm lens would be 150/52 or 2.88X. That formula is for 35mm cameras only. For simplification, the most used formula is X = mm/50 or 3X for our 150mm lens and we say that it magnifies 3 times.

For digital cameras, one has to correct by the Focal Length Multiplication factor (FLM). The formula is FLM = 36 / (sensor length). A 35mm camera film measures 36mm x 24mm while the sensor of a Canon 20D DSLR measures 22.2mm x 14.8mm. This gives us a FLM of 36 / 22.2 = 1.62. Our 150mm lens would become about 5X on a 20D.

The exact formula would be X = (lens in mm) / 52 x 36 / (sensor length). In our example, it would be X = 150 / 52 x 36 / 22.2 or exactly 4.67775X.

Sensor sizes are explained here:
http://www.dpreview.com/learn/?/Glossary/Camera_System/sensor_sizes_01.htm

Focal Length Multiplication factor is explained here:
http://www.dpreview.com/learn/?/Glossary/Optical/Focal_Length_Multiplier_01.htm

Please correct me if I'm wrong.

 

[Paul Corfield]

Thanks Jules. I must admit it's not something I was sure on. All I did was look up some 10X optical zoom digital cameras and they all seemed to be around 360mm equivalent so I just based my answer on that.

Paul.

 

[Trinie]

Kuldoode,
I think you should look into the D40X which is a follow-up to the D40. It may cost a bit more but twice as many pixels plus extras. You have to go to one of the camera sites to compare them.

 

[Kuldoode]

Jules,

Lets see if i have a grip of this now:-

Nikon d40 - Sensor Length = 23.7

A lens of 300mm would give me 300/52 * 36/23.7 = 8.76 times magnification ?

if thats correct and i put a x2 telecoverter on does it then have a mag factor of 17.52 ?

Next question, what does this mean:-

Lens thread -- Nikkor AF / F-mount, D-Type ( is this a common thread ).

Sorry for the perhaps silly questions but before i start forking out for a more serious camera i need to know as much as i can, after all it is the start of a camera system i will be buying and i just want to get the best i can for value of money.

Thanks, i will take a look at the D40x but i was informed that after 6 Meg pixel heat and noise become more of a problem. Is there any truth in that ?

Like your site Jules, some lovely pictures.

regards

 

[Trinie]

Paul,

That's a beautiful shot of the moon. The details are incredible, it is so edge sharp. You must have very clear skies where you are.

 

[Kuldoode]

Guys ,

From what you have told me, if i were to use the below cameras with the lens and teleconverter shown i would get the below mag factors, this would indicate that the olympus was better ?


Lens Length 300
Teleconverter 2

----------------Lens----- Sensor length ------- Multiplication Factor
Nikon d40-------52 ---------- 23.7 ----------------- 17.5
Pentax K100D---52 ---------- 23.3-------------------17.8
Olympus 410----52 ---------- 18---------------------23.1
Canon 400D-----52 ---------- 22.2-------------------18.7


Any advice would gladly be taken as i dont want to purchase the wrong thing. If i was attaching any of these to my scope ( 20 - 60x ) what would i need to look for in the cameras abilities ?

regards