What else do I need for my 55mm backfocus?

[Guest]

Hi,

I currently use an SW 72ED Pro with Orion short field flattener ( https://uk.telescope.com/catalog/search.cmd?form_state=searchForm&siteCode=UK&keyword=field+flattener) and Canon 600D. The 600D with T ring creates exactly 55mm of backfocus which is exactly what is needed for the field flattener.

I am looking to order:

Altair 183M Pro Camera (+12.5mm backfocus?)

Sky-watcher 5 Position Manual Filter Wheel (+20mm)

I assume I will have the camera, then the filter wheel, then any additional spacers to create 55mm backfocus, then the flattener, then the scope.

I am trying to work out what additional spacers and accessories I will need that do not already come with the camera or filter wheel.

I believe all I need is to space another 12.5mm(?). I think a T-2 10mm extension and then padded with some thin T-2 adjustment rings but I am not convinced I have my calculation or what I need correct!

Any assistance would be great appreciated.

[MarkAR]

Sounds more like 22.5mm. 

[Guest]

You are indeed right @MarkAR, 22.5 it is!

[Astrosharkey]

https://www.firstlightoptics.com/adapters/baader-t2-extension-tube.html

 

7.5mm and 15mm together = 22.5mm