Quote:
Originally Posted by Joshua Bunn
When the metal backfocus is quoted as 44mm, is it referring to where the image comes to focus behind the mounting surface of the lens OR is it referring to the position of the senor inside the camera body (44mm below the camera mounting surface?) If its the later, this could explain it, because there are filters inside a camera that will increase the length of the optical path, which may not be the case so much with your ASI camera. just some thoughts ...
Joshua
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This is a very good point that you are raising here Joshua. The physical back spacing on the Canon EOS series is definitely 44mm as measured from where the lens joins the camera body and the plimsoll line on the camera body (I've checked my 60Da and 80D to be sure!). However, it is correct that there are filters in this light path which means that the actual focal point is altered by the inclusion of the filters I do wonder about the Astronomik 50mm round filters as well as they are 1mm thick and have a specified optical thickness of 1mm as noted on the Astronomik web site. And in addition there is the possible variation in specification of the set back distance in the ASI6200 camera.
The good thing is that I have a configuration that is now working. Alas, the inevitable has happened and the Central West of NSW is now clouded out and raining <sigh>