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p.2 #2 · p.2 #2 · Starburst issue with Sony sensors (A7r) how big is it? | |
The determining factor for the shape of diffraction stars is the shape of the aperture. A straight edge produces a streak of light radiating out in two opposite directions. When the aperture is nicely symmetrical, the number of blades N gives the number of spikes in the star (2N for odd N and N for even N). When the symmetry is poor and/or the blades are rounded, however, the star can get messy. One regularly sees N double spikes for even N, for instance, and a broadening of the spikes away from the center.
One should be careful with drawing conclusions from a comparison of night shots with different lenses under different conditions. The intensity difference between a star and its surroundings easily varies by a factor of 10 or 100 (or whatever) between shots.
If the cause of the clutter in the star region is an optical one (microlenses, reflections, etc.), I don't think there should be big differences between lenses. Otherwise, I cannot exclude aliasing and lossy compression as causes at this point. And what about the deconvolution sharpening that Sony supposedly applies in the A7r? Maybe it is only used for JPEG file dumps, I don't know, but I would expect visible artifacts in highlight regions. (In this case the garbage presumably only occurs when the camera knows the lens aperture.)
There is need for controlled tests to more shed light on this matter.
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