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Yep...
It may also be a bit of wrong secondary offset...
Because the light beam reflected from primary is conical, for it to pass the secondary unaffected by vignetting, it needs to be positioned a bit away from focuser (2~4mm, depending on f/ ratio and other factors).
I intend to use my Newt for AP, so I will replace existing secondary with larger one - and adjusting the correct offset will be even more important part of colimation process.
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