Help with back focus on Esprit 100 and Red cat please

[Neil27]

Come back to this hobby after a hiatus of around 10 years to so. Previous attempts were with a Canon 450d and it worked.

Fast forward to now and I have an Esprit 100 (with flattener) and a red cat 51 scope.  Camera is the QHY268C, No filters yet as deciding what I need best for my skies, states bortle 4!

So advice please on correct spaces and adaptors for achieving back focus with the Esprit / flattener and same question for the red cat. I’ve searched online and looked at many diagrams from QHY, I think I have the answers, (55mm back focus from flattener to chip) and the diagram I am using is the one attached, kit D1. Just would love someone to confirm I am on the right track.

Also found this useful adapter for using 2 inch filters with the esprit flattener, anyone else use it? https://www.firstlightoptics.com/adapters/astro-essentials-filter-cell-adapter-for-sky-watcher-esprit-flatteners.html

Next question does anyone have experience of attaching a QHY268C to a red cat, if so how did you do it and get a 2 inch filter into the imaging train?

Thanks for reading,
 

 

[geeklee]

2 hours ago, Neil27 said:

Next question does anyone have experience of attaching a QHY268C to a red cat, if so how did you do it and get a 2 inch filter into the imaging train?

HI Neil - for the RedCat 51 - at least the current version - you can unscrew the M48 adapter piece at the back and it will reveal a place to screw in a 2" filter.  Then replace this back on the RedCat and you've still got your M48 adapter to connect the camera - assuming it has M48, which it seems to above?  Picture from WO here showing filter position.

Due to the Redcat's design, a fixed back focus isn't the case.  I like the information in section 4 here (scroll down) - there's a nice diagram from WO too 👍

I still aim to have my cameras around 55mm (but have had 53, 54 & 56 with no difference).

Edited February 2, 2022 by geeklee

[Neil27]

Thanks Lee for the help, appreciated.

Great illustration from the websites you linked and it explained it very well.

I should receive the RedCat tomorrow all being well, no doubt with a dose of clouds, apologies for that 🤐😊

[The Lazy Astronomer]

6 hours ago, Neil27 said:

Come back to this hobby after a hiatus of around 10 years to so. Previous attempts were with a Canon 450d and it worked.

Fast forward to now and I have an Esprit 100 (with flattener) and a red cat 51 scope.  Camera is the QHY268C, No filters yet as deciding what I need best for my skies, states bortle 4!

So advice please on correct spaces and adaptors for achieving back focus with the Esprit / flattener and same question for the red cat. I’ve searched online and looked at many diagrams from QHY, I think I have the answers, (55mm back focus from flattener to chip) and the diagram I am using is the one attached, kit D1. Just would love someone to confirm I am on the right track.

Also found this useful adapter for using 2 inch filters with the esprit flattener, anyone else use it? https://www.firstlightoptics.com/adapters/astro-essentials-filter-cell-adapter-for-sky-watcher-esprit-flatteners.html

Next question does anyone have experience of attaching a QHY268C to a red cat, if so how did you do it and get a 2 inch filter into the imaging train?

Thanks for reading,
 

 

55mm is correct for the Esprit.

Just because it caused me a brief moment of confusion, make sure you measure your backfocus from the adaptor on the back of the flattener, not the flattener itself:

[Neil27]

7 hours ago, The Lazy Astronomer said:

55mm is correct for the Esprit.

Just because it caused me a brief moment of confusion, make sure you measure your backfocus from the adaptor on the back of the flattener, not the flattener itself:

Thanks LA,

I think I have it sorted, adaptor kit has been ordered. QHY do make it difficult trying to sort out b/f looking around the web, ZWO certainly appear to be ‘adaptor’ friendly.

Thanks for the advice though, appreciated.