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Old 24-05-2019, 06:48 PM
Stefan Buda
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Stefan Buda is offline
 
Join Date: Jul 2013
Location: Melbourne, VIC
Posts: 823
Quote:
Originally Posted by HenryNZ View Post
I read from CN that QSI has a backward definition of “back focus” which often causes confusion. The adjustments in the table is meant to be made to the optical length of the camera. Therefore, if you add a filter you make a negative adjustment to the optical length, which in effect means you need a longer adaptor to make up for it. I can’t find the thread on CN now but it seems to be a recurring question posted on CN from time to time.
What a relief to hear that. Thanks, you saved my sanity. It is a very screwed up reasoning because the overall optical train gets longer by one third of the filters thickness.

Quote:
Originally Posted by DavidTrap View Post
I just followed the instructions. If you have Astrodon filters (3mm thick), take 1mm off the recommended length of the adapter.

DT
In that case you went in the wrong direction with the length of your adapter.
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