I apologize if this is a really silly question but just want to confirm a few things. I was told that for my Nikon DSLR I needed to "unscrew and lengthen" the Flat61A by 12.9mm to position the sensor exactly to hit the image plane. Then to get stars sharp on my camera I had to focus out the R&P focuser to around a value of 31 on its markings.
1) If this doublet APO scope is just two glass elements at the front converging light to a specific spot based on its focal length, why do I need an exact value of 12.9mm on the Flat61A if I still need to just adjust the DLSR sensor's position using the R&P focuser to move everything? Is this to allow focusing at the closest possible distance? So then my 12.9mm along with moving the focuser all the way out to 31 is for "infinity focus" only?
2) Could I add something that is 17mm wide in my optical train (filter drawer system) even though its more than 12.9mm extension of my Flat61a? Could I add it in, take out the 12.9mm and put it back to 0, and then make up the remaining 4-5mm from my focuser movement and maybe only come out to roughly 26-27 instead?
Edited by OldSchoolAstro, 25 September 2020 - 08:18 AM.