Back-Focus distance

john_gill

Hi,

I am using an APM apo 107/700 scope, a 2" TS flattener and the ASI1600MM-Pro with the 7 position filter wheel and 36mm filters. The ZWO site shows the 55mm back-focus but the APM site shows 111mm for back-focus.

Which is the correct distance for proper back-focus and are the filters par-focal (NB & LRGB)?

Regards

John

john_gill

Hi Martin,

I had a look at my TS flattener and it is the 2.5". What is your BF distance with the APM and TS Flattener. I also use the Riccardi 0.75 reducer/flattener (this is the one that fits inside the scope) and I think the BF is 80mm.

If you have other info, it would be appreciated.

Regards

John

katherine.tsai

I agree with artem.