Hello. I am going to change up my imaging rig to include (once again) a Takahashi QE 0.73x focal reducer. It has a critical metal back distance of 72.2mm. The STT manual states the back focus of the STT8300M+FW8G-STT filter wheel is 54.06mm. So, I will need an adapter extension tube to reach this critical focus: 72.2mm - 54.06mm = 18.14mm + 1mm (for 3mm Astrodon filters) = 19.14mm My question is this. Does the aforementioned 54.06mm take into account the thickness of the CCD cover plate? Am I correct in assuming, based on the 3mm thickness of the Astrodon filters I employ, that I do in fact need to add 1mm additional length to my adapter? This is correct, yes? The extra 1mm will not affect luminance images? Said another way, am I adding too much extra? I had read in another posts where the 72.2mm was very important to achieve, but tossing in the filters has me worried and confused. Or am I over thinking this? Thanks! Chris
Referring to http://diffractionlimited.com/wp-content/uploads/2016/11/backfocus.993x0.gif These are optical distances. So an STT + FW8G and 3 mm filter is 52.5 mm total.
Doug: I am SO glad I posted up here! So, with a bolt-on Precise Parts adapter, I am good at 52.5mm into my equation.... Chris
Hi! I am working out the necessary adapters for my C14 EdgeHD + STT8300/F8WG. The manual states: 54.06 mm The table above 52.5 mm Why this apparent discrepency? Thanks! Francois
