Esatto 2" focuser + EdgeHD 11 + ZWO OAG-L + 2600MM Pro

[oymd]

I'll be immensely grateful if someone can advise on this imaging train.

After experimenting with imaging with the Edge HD, mirror flop and shift, I decided to by pass the issue entirely, and LOCK the mirrors, hence purchasing the Esatto.

Can you please recommend which adaptor will be used on the CAMERA side? And how to reach correct back focus of 146mm?

The OAG I am using is the newer OAG-L, with the 12x12mm prism and 48mm aperture.

Camera is the 2600MM mated to the 2" EFW.

Here's my imaging train:

 

TWO OPTIONS. One WITH, and one WITHOUT 0.7X Celestron reducer.

 

EdgeHD 11 ===> 0.7X Reducer ===> Esatto 3.3" adaptor ===> Esatto 2" Focuser ===> ?? ===> ZWO OAG-L  ===> ZWO 2" EFW ===> ZWO 2600MM Pro

 

EdgeHD 11 ===> Esatto 3.3" adaptor ===> Esatto 2" Focuser ===> ?? ===> ZWO OAG-L ===> ZWO 2" EFW ===> ZWO 2600MM Pro

 

Many thanks

[MikeBY]

You cannot put a focuser between the reducer or telescope and camera.  You mess up the backfocus..

[oymd]

6 hours ago, MikeBY said:

You cannot put a focuser between the reducer or telescope and camera.  You mess up the backfocus..

Good morning

Sorry, I am not following?

The Esatto 2" focuser has been widely used with the EDGEHD scopes and the reducer?

[michael8554]

If you put the focuser between the reducer and telescope, the reducer's backfocus will change as you alter the focus !

Michael

[MikeBY]

On 07/02/2023 at 02:39, oymd said:

Good morning

Sorry, I am not following?

The Esatto 2" focuser has been widely used with the EDGEHD scopes and the reducer?

Well, if you want to be consistent getting the best performance it's problematic technically speaking.

But so is being out of focus.

So if we're careful it is ok.  We just have to be mindful about what it's doing.

Most SCTs, are quite tolerant about backfocus. They work across a fairly wide range without much impact.  That is until we add a focal reducer/flattener. At that point we have keep the backfocus at a set point to get the expected results. 

The EdgeHD has the corrector built in so we are stuck needing to keep backfocus at 146mm. If we stray too far off that there's an impact. 

If we're designing an optical train for one, sure a microfocuser in front of the OAG that has sub-micron steps is great. 

They do take up backfocus  and we also need it to behave as if it has a fixed length so that we stay at the right backfocus.

That last part is on the us.  It's up to the us to get a very close pre-focus with the scope and watch the microfocuser position to be sure we aren't shifted too far.