Just reaching out to the IIS brains trust.
I have a Vixen PH corrector, the stated back focus distance is 56.6mm
https://www.skypoint.it/en/ota-refle...-095x-f38.html
I am using a ZWO ASI1600, which has a 55mm back focus.
Question: Which one should I be aiming for?
I am inclined to go with the corrector spacing (56.5mm) as that would achieve the stated flat field.
Over to you!
thanks
Bo