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A de defocused star or a dowble reflection focused star, will always show the shadow of the secondary in the midle when stars are in the middle frame. As stars move out to the edge, the shadow also moves, this is normal, as you are moving "Off axis". This is where you start paying dollars for the scope.. As properly corrected scopes will still show pin point stars when focused all the way to the edge, and the reflected double image or if out of focus will show the secondary shadow near the edge when the star is near the CCD edge.
I hope this makes sense.
Theo
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