A (for me) a big question about back focus adjustment to allow for 1mm thick filters ????

[SlimPaling]

Hi ...

I need to tweek the back focus between the flattener on my f6 APO scope and my Moravian CCD camera to compensate for my 1mm thick filters.

I have seen on the 'net that some people say that I need to increase the back focus by 1/3 of the thickness of my filters = 1/3mm

However when I asked the manufacturer of my flattener & scope ( APM Scopes ) he suggested that I need to add 1mm to my back focus.

Before I start to take my kit apart ..... does anybody have any suggestions which of the above is correct?

Mike

[Elp]

It's usually a third but +1mm works as a general amount. No glass is built equal due to manufacturing tolerances so you'll have to test and find out, you might find the actual true backspacing figure is much different than stated in relation to fractions of mms.