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In addition to Greg's post one of the unfortunate aspects of using camera lenses is that while they may perform satisfactorily on terrestrial subjects, the off axis aberrations show up with a vengeance on astroimages even on small sized chips.
I have no issues with my Pentax 300mm and 70mm lens on an STX-10ME, but a recently purchased Pentax 43mm f/1.9 is an absolute disaster even when stopped down to f/4.
According to the Photozone review it should be a "star" performer.
I sent the lens back which was checked against the ISO12233 test chart (see attachment), the conclusion being there was nothing wrong with the lens.
In response I sent them a test image of a star field taken with a Pentax k-r, which they refused to except it has valid evidence.
Currently the issue is unresolved.......
Steven
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