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Hi Bart,
This is what I did with a Lodestar guide cam and Orion thin OAG.
First up get the imaging camera (QHY12) set at perfect focus and measure the distance from the shoulder of the focuser to the end of the drawtube where the thumb screws are. I used a digital caliper but a short ruler would work.
I then did the same thing again but this time getting the lodestar at best focus and then measure that distance.
In my case there was a 2mm variance i.e the lodestar focal point was 2mm longer than the QHY12 focal point.
Now I could have added a 2mm spacer to the QHY12 but that would upset the 55mm distance required for the coma corrector to work. Instead I had to shorten an aluminium spacer on the Orion OAG by 2mm with a grinder. And then all good.
All the best and I hope you can get it sorted.
Bill
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