Hello everyone.
I use a QHY8pro and a Skywatcher Evo 80ed scope but I am not happy with the misshapen stars in the corners. Looking around at field flatteners I have settled on the HoTech 2"SCA field flattener from here:
http://agenaastro.com/hotech-2-sca-field-flattener.html
It requires 56mm of back-focus to the camera CCD. According to the QHY8pro manual the CCD has 20mm of back focus therefore a 36mm spacer is required, no problem.
However, my QHY8pro differs from the one mentioned in the manual (maybe mine is an earlier revision, I am not sure). My camera doesn't have the tilt/centre adjustment or the hole for the desiccant tube.
So I am a little confused as to what extra spacing I require so maybe I should just get this :
http://agenaastro.com/baader-variloc...e-29-46mm.html
From what I can see the combination of these two should do the job. Have I got this right or is my understanding of back-focus completely wrong.
Thanks
Jeremy