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DSLR adapter for a 90deg binoscope?

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#1 zerodur

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Posted 11 August 2020 - 05:49 AM

Does anyone have experience taking photos through a binocular telescope with a DSLR?

 

I only want an occasional shot of the moon, figure it can't be worse than holding an iPhone to a Pentax XW5. I already have the scope, and my Nikon D700 (full-frame) is gathering dust. I have a 200mm f/2.8 lens so I have an idea of what various objects look like through that lens, but I have no idea what things look like through the binoscope (70mm, 90deg APM ED APO, fl=400mm) or whether/how it would come into focus at all. Ignoring stuff like edge brightness or field-flatness, would the moon be recognizable at all through the camera?

 

I know the first advice to newcomers for astrophotography is always "don't", hence I post this here instead of over "there". I enjoy two-eye viewing too much; can't justify an astrograph just for a snapshot... (also saving for a swaro NL grin.gif ).


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#2 Mark9473

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Posted 11 August 2020 - 06:44 AM

I would think that to reach focus, the camera sensor needs to be where the eyepiece fieldstop normally is.

Sounds like you'd need a barlow or relay lens or such.

 

I think you can do worse than holding an iPhone to an eyepiece.



#3 TOMDEY

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Posted 11 August 2020 - 08:17 AM

With a binoscope that comprises proximate prisms just before the focal plane, there is no practical way to get a negative amplifying relay (aka Barlow lens) down in there. That leaves the option as a positive relay. Note that looking through an eyepiece with a iPhone is a positive afocal relay, where the combination of eyepiece + integral iPhone lens, in combination, define that compressive positive relay. The iPhone array is miniscule; your DSLR array is comparatively huge. To shoot the moon through your APM binoscope, you will need to use an appropriate eyepiece afocally with a lens on your DSLR. For your full-frame to avail the full-field of your binoscope, I would recommend an eyepiece that presents a 50o AFOV and a ~25mm lens on the full-frame DSLR. You will need to have enough eye-relief on that eyepiece to be able to place the entrance pupil of the DSLR lens there, at the exit pupil of the eyepiece. Try that as a starting point.

 

I've done that, and it works well. I can work out the details; that's what you should do. If you do the computations ahead of time, that eliminates all the fiddling around at the scope. Ummm... really should buy or (more likely build) a mechanical coupler/adapter twixt camera lens and eyepiece. That way you just slide that whole thing into the bino for taking pictures.

 

NOTE: It is especially useful if your DSLR parked there does not block access to the other eyepiece. That way, you can use the other side as a 1x viewer/finder... so what you see there is what you are capturing with the camera... no surprises.    Tom


Edited by TOMDEY, 11 August 2020 - 08:18 AM.

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#4 zerodur

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Posted 12 August 2020 - 03:52 AM

Thanks Tom. It sounds like it's a bit more involved than getting a random M42-1.25" T-ring off some online store. Also got some reading to do ("positive/negative relay"). I have not operated a refractor or used a barlow lens before. You mentioning using an eyepiece + DSLR lens does remind me of that post, though I couldn't find an adapter from that XW (43mm, pitch unknown?) thread to anything other than Pentax' own system (the closest I have is a Nikkor 50mm f/1.4 with 52mm thread). Guess I have to settle with "live viewing only" for now.



#5 Mark9473

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Posted 12 August 2020 - 06:45 AM

Some Baader eyepieces are known for having a T2 thread at the eyecup side.


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