11 replies to this topic

[stevecoh1]

I've purchased a used Celestron AVX Schmidt-Cassegrain scope and a ZWO ASI533 Camera. What is the proper adapter needed to connect these? That adapter is not included among those included with the camera.  I bought the scope from one dealer since it was used and the camera from another. It is almost impossible to google this question.

 

Thanks

[DirtyRod]

Which adapter depends on what’s in your imaging train. You didn’t say which scope bit I’m going to assume it’s an 8” SCT so you first need an SCT adapter to attach to the scope and then need to step down to an M42 adapter for the camera. Im using a filter drawer directly in front of the camera which screws into a female to female 11mm M42 adapter which came with the camera.

 

I assume you know that you are going to need the proper backfocus for the camera to work properly. If you are running a reducer on the scope then you need 105mm for most SCT models and between 133mm and 146mm depending on whether you have the 6”, 8”, or 11” SCT. You can’t just attach the camera directly to the scope.

 

If you are not familiar with backfocus then I’d give the following link a read. Agena Astro has all kinds but which you need depends on how your imaging train is set up.

 

https://astronomy-im...33mc-pro-color/

 

 

 

 

[bobzeq25]

Trivial.  The SCT should have an eyepiece adapter, hopefully 2 inch.  This piece goes in at the plain end, and takes the camera at the threaded end.

 

https://www.amazon.c.../dp/B07D2ZMWGN/

 

They also make them for 1.25, that will likely vignette.

 

Not trivial at all.  Getting that very inexpensive mount and an 8 inch SCT to track astrophotography targets well for doing astrophotography.  Might work for EAA, but won't for traditional imaging.  Classic example of the "too big a scope on an inadequate mount" beginner mistake.  Seen over and over and over...  Extremely common result:

 

"I regret spending the first 6 months trying to learn imaging with an 8" Edge, with that scope it was a losing effort. Fortunately got a nice little refractor, and not only have the quality of my images improved but I'm actually enjoying the process of learning how to do it!"

 

That was traditional imaging.  EAA could maybe work.

Edited by bobzeq25, 17 September 2023 - 11:16 PM.

[stevecoh1]

Which adapter depends on what’s in your imaging train. You didn’t say which scope bit I’m going to assume it’s an 8” SCT so you first need an SCT adapter to attach to the scope and then need to step down to an M42 adapter for the camera. Im using a filter drawer directly in front of the camera which screws into a female to female 11mm M42 adapter which came with the camera.

 

I assume you know that you are going to need the proper backfocus for the camera to work properly. If you are running a reducer on the scope then you need 105mm for most SCT models and between 133mm and 146mm depending on whether you have the 6”, 8”, or 11” SCT. You can’t just attach the camera directly to the scope.

 

If you are not familiar with backfocus then I’d give the following link a read. Agena Astro has all kinds but which you need depends on how your imaging train is set up.

 

https://astronomy-im...33mc-pro-color/

Yes, sorry, it’s the 8” SCT on the Advanced VX mount.  
 

Right now, I’m just trying to attach the camera to the optical tube. Reducers and such improvements are down the line a bit. Right now I’m just trying to get the basic connection

You mention an SCT adapter. I think that’s the piece I need. Is that the same as the SCT “T-Adapter” that Celestron sells? The info on that says that it’s for DSLR cameras, which is not what I’m trying to attach. or is it something else?

 

Thanks for the help.

[DirtyRod]

Yes, sorry, it’s the 8” SCT on the Advanced VX mount.  
 

Right now, I’m just trying to attach the camera to the optical tube. Reducers and such improvements are down the line a bit. Right now I’m just trying to get the basic connection

You mention an SCT adapter. I think that’s the piece I need. Is that the same as the SCT “T-Adapter” that Celestron sells? The info on that says that it’s for DSLR cameras, which is not what I’m trying to attach. or is it something else?

 

Thanks for the help.

The T-Adapter for the 8” is what you need to start. It will adapt the SCT telescope end to M42 but it has a male connector as does the 533. The camera came with an 11mm female to female adapter which you will need to connect the camera to the T-adapter.

 

That said, the T-adapter is two parts for a total of 78mm. The camera has a 6.5mm backspace. Without a reducer, the scope needs about 133mm of backspace to focus. If you just bolt the camera plus an 11mm spacer onto the 78mm t-adapter you are at 95.5mm and it will not come to focus!

Edited by DirtyRod, 18 September 2023 - 12:57 AM.

[stevecoh1]

The T-Adapter for the 8” is what you need to start. It will adapt the SCT telescope end to M42 but it has a male connector as does the 533. The camera came with an 11mm female to female adapter which you will need to connect the camera to the T-adapter.

 

That said, the T-adapter is two parts for a total of 78mm. The camera has a 6.5mm backspace. Without a reducer, the scope needs about 133mm of backspace to focus. If you just bolt the camera plus an 11mm spacer onto the 78mm t-adapter you are at 95.5mm and it will not come to focus!

Thanks for this info.

 

Besides the 11mm spacer the camera also comes with 21mm T2 extender. See manual, p.4. So that would boost the length to 116.5 mm, closer, but no cigar, to your total of 133 mm.  Where do you get that 133 mm figure?  I can find no documentation in the manual or anywhere else that mentions this distance but maybe I'm not reading things correctly.  How do you know this?  Experience or something you've read somewhere?  I would like to order all the equipment I'll need, maybe a reducer too. I wish the manufacturer would indicate WHY they've included the extenders they have and what they're for.

[DirtyRod]

Thanks for this info.

 

Besides the 11mm spacer the camera also comes with 21mm T2 extender. See manual, p.4. So that would boost the length to 116.5 mm, closer, but no cigar, to your total of 133 mm.  Where do you get that 133 mm figure?  I can find no documentation in the manual or anywhere else that mentions this distance but maybe I'm not reading things correctly.  How do you know this?  Experience or something you've read somewhere?  I would like to order all the equipment I'll need, maybe a reducer too. I wish the manufacturer would indicate WHY they've included the extenders they have and what they're for.

Other than imaging with an 8" SCT and that same camera for about 3 years, I'm sure it's somewhere on the Celestron site or in the manual. The 105 is definitely on the reducer web page. I don't know if you have the Edge or the standard C8 but if you Google you will see a ton of responses with those figures. It's an approximation as every scope is different and mine needs 106.6mm with a reducer and 134mm without. Because it's a trial and error you will find that many imagers have a box of spacers of all sizes to get the exact configuration. As you can see below I have 6 cameras and multiple OTAs, usually run a reducer, sometimes not, with filter drawers, etc so buying a set of spacers is generally a good thing. 

[stevecoh1]

Thanks.

[DirtyRod]

Top of Page 11 for the 8" Edge without the reducer.  

 

https://celestron-si...English_web.pdf

 

I don't have a standard C8 but I assume there is some kind of back focus requirement. Maybe someone with one will confirm if it's the same 133 or something else. I suspect that most people are running with a reducer for most imaging.

Edited by DirtyRod, 18 September 2023 - 02:43 PM.

[stevecoh1]

Top of Page 11 for the 8" Edge without the reducer.  

 

https://celestron-si...English_web.pdf

 

I don't have a standard C8 but I assume there is some kind of back focus requirement. Maybe someone with one will confirm if it's the same 133 or something else. I suspect that most people are running with a reducer for most imaging.

That level of engineering documentation is not available in the manuals for the C-8. That's what I was looking for. Oh, and it's page 13.

Edited by stevecoh1, 18 September 2023 - 03:02 PM.

[mclewis1]

The standard SCT will come to focus anywhere from almost right up against the rear baffle opening and over 6" behind it ... when you don't have any additional optics (reducers, etc.) you don't care much about "back focus" on an SCT. Celestron documents an optimal focal point as approximately where the scope comes to focus with a 1.25" SCT adapter, and 1.25" diagonal. This "optimal" point is where the optics are evaluated while the scope is being manufactured so it's usually considered the point of best optical figure. However the difference between this point and one 50mm inwards or outwards is miniscule as in you would be hard pressed to measure it let alone see it in deep space images.

 

If you're not using a focal reducer one simple choice is to just use the Celestron SCT T-adapter. It's very simple and solid, and provides about 50mm of spacing to the T thread, (and then there is the 6.5mm in the camera itself). The adapter ends in a male T thread, the camera has a female T thread. The adapter also allows you to rotate your camera before tightening down the connection to the scope.

 

The SCT f6.3 focal reducer requires a very specific amount of spacing (around 105mm). other reducers do too but the amounts are different.  Ideally you want to  have the flexibility to handle a variety of different configurations (reducers, filters, etc) and while there are a number of different methods of doing this the most popular for most folks has been a selection of T thread spacers.

[stevecoh1]

Thanks. I’ve got the T on order and that seems like a good place to start. I suppose that if it was that important they would have put in in the manual.