Quote:
Originally Posted by HenryNZ
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.
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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
I just followed the instructions. If you have Astrodon filters (3mm thick), take 1mm off the recommended length of the adapter.
DT
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In that case you went in the wrong direction with the length of your adapter.