Just setting up my 152mm refractor to work with the Hotech Flatterner and am finding the various historical threads about spacing a bit confusing. The flattener has a requirement for 55mm of spacing to the sensor, and that's pretty straight forward, however research tells me that I need to follow the 1/3 rule - meaning I need to add spacing to compensate for the affect of the filter in the imaging path. My 2mm filters, would need an additional 0.66mm of spacing added to the path in front of the filter. I can make up spacing that is close to that (0.33 close) and could use some thin Delrim spacer washers to get it spot on, but how much leeway do i have, is 0.33mm close enough, how exact does the spacing need to be?
Secondly, what allowance, if any, needs to be made for the cover glass window in the end of the camera (an ASI1600)? The window seals the sensor chamber, but I do not know how thick it is (probably about 1mm). Does that need to be seen as a filter and affecting the spacing?
