Folks I have a random, but topical question on BackFocus, given that i have a Reducer/Flattener asking for 55mm, and Camera Sensor to Flange distance of 17.5 leaving me to fill a gap with 37.5 mm of spacers what sort of 'Tolerances' am i working with, will simply purchasing an Astro 7.5mm and 30mm tube spacer do the job and that the Astro industry has the tolerances all buttoned up with acceptable parts or will there inevitably be some fine tuning required when the images start to tell a story. OR, is the Reducer/Flattener more tolerant of a little stackup error in the parts. for me it comes down to whether I go with an adjustable Tube spacer or Fixed .
some insight appreciated, apologies to all if i missed the pertinent sentence some place.
Gary ( am kinda just setting up with the hobby )