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ZWO ASI294MC Pro to Celestron EdgeHD 8"

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#1 Firstround

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Posted 12 June 2019 - 05:43 PM

I have been using my ASI294MC P for a short time with my refractors with success but I am having a hard time with how to attach to my Celestron 8" EdgeHD straight back out from the rear cell without using the focal reducer. I do have the Celestron T-adapter but the ASI won't screw directly into it without some type of adapter. Any ideas what I can do? I did manage to attach the ASi to a 2x barlow then it into the diagonal without using the focal reducer and worked fine for some Moon shots and I am also able to install the ASI directly to the focal reducer.



#2 PeteM

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Posted 14 June 2019 - 08:14 PM

Do you have a 2" visual back? I use mine with a 2" nose piece attached to back of my RC with the TCF-S focuser attached.



#3 donstim

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Posted 17 June 2019 - 10:34 AM

It sounds like you are removing the visual back? Doesn't the visual back have the same threading as the focal reducer? When you say you can install the camera directly to the focal reducer, I assume you mean by using the celestron t-adapter. I would think it would be the same thing to attach it directly to the visual back. At least that's the way it is with my non-Edge HD Celestron 8" scope.

 

[Edit]  The T-adapter screws directly on to the back of the scope with the visual back removed.  (It will also screw directly onto the focal reducer - same threading on my scope for the back of the scope and the back of the focal reducer.)


Edited by donstim, 17 June 2019 - 12:17 PM.


#4 jgraham

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Posted 17 June 2019 - 11:58 AM

I use a 2" visual back on the scope and a 2" nosepiece on the camera. When using a focal reducer I mount the focal reducer first, then the visual back, and then the camera.



#5 donstim

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Posted 17 June 2019 - 12:15 PM

Oops, I was mistaken in my description.  The T-adapter threads directly on to the scope after removing the visual back.  It also threads directly to the focal reducer without using a visual back or a nosepiece for the camera.

 

The EdgeHD uses a different T-adapter.  Do you have the T-adapter made specifically for the EdgeHD? I would assume the threading on the back of the scope and on the back of the reducer would be the same such that the T-adapter would thread on to either one.  That's how it is with the non-EdgeHD scopes.


Edited by donstim, 17 June 2019 - 12:15 PM.


#6 t-ara-fan

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Posted 17 June 2019 - 09:44 PM

Get the White Paper on EdgeHD.  Page 14 tells you backfocus from flange is 133.35mm.

 

The T adapter's flange is 55mm short of that ... designed so a T-ring and DSLR have the right backfocus with no extra adapters.

 

So the T-adapter is 78.35mm long.  You need 55mm to your sensor.

 

Your camera has a 6.5mm flange-to-sensor distance  (scroll down to mechanical diagram) and the camera comes with a 11mm T2 ring.  That makes 17.5mm to your sensor. 

 

You need another 37.5mm.  Coincidentally you also got a 21mm T2 and a 16.5mm M48-T2 extender with your camera, plus a M42-M48 adapter.

 

Summary:

  • Celestron T-adapter on the back of the scope.
  • M42-M48 adapter on the T-adapter
  • M48-T2 16.5mm long extender on the M42-M48 adapter
  • 21mm long T2 extender on the M48-T2 16.5mm extender
  • 21mm long T2 extender threads into your camera that has the 11mm T2 ring screwed into it.

Edited by t-ara-fan, 17 June 2019 - 10:09 PM.

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