Starting to play with planetary imaging.
Most ZWO/ASI cameras require a back focus of 55mm. (I understand what this is)
I plan on using this on my C8 with a 6.3 FR. and a 2X Barlow.
I am not sure how the Barlow works into the total back focus distance.
I am assuming that I need to remove the Diagonal.
Would my set up be: Scope -->Focal Reducer-->Visual Back-->Barlow-->Camera?
I would think I need some spacing in there somewhere.
ZWO has a page about Back focus https://astronomy-im...tions-55mm.html
No, the camera does not have a back focus, the camera requires that the image falls on the sensor and that is all.
That image is usually defined as a distance from some machined face, and the distance from that face to the focal plane is the back focus.
Your FR probably has a back focus specified and being for an SCT I do not expect it to be 55mm - what does the specification of the FR state???
If you add a barlow in then all bets are off.
Firstly the focal plane will be somewhere undefined and secondly it will likely no longer be flat.
The really big question is why use a FR to reduce the image size, then add a barlow in to increase the image size?
Just seems utterly pointless, and expensive.
So I would expect an FR and a barlow to result in a non-flat non-reduced image on the sensor at some undefined distance. You are not the only one Slightly Confused.