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| | Pnmctrfilt: Centre filter for portable pixmaps |
 | | A centre filter has many advantages: not only does it automatically correct for full-frame images but, since it's fixed to the front of the lens, it also compensates for the off-centre vignetting which occurs when camera movements are employed for perspective or plane of focus adjustment. |
 | | Many centre filters require a 1.5 or 2 f-stop filter factor adjustment, which may, in turn, necessitate a shutter speed so slow (since wide angle lenses, even with centre filters, are best used at apertures of f/16 or smaller) that hand-holding the camera is impossible and motion blur becomes a problem when photographing moving objects. |
 | | Many centre filters require a 1.5 or 2 f-stop filter factor adjustment, which may, in turn, necessitate a shutter speed so slow (since wide angle lenses, even with centre filters, are best used at very small apertures) that hand-holding the camera is impossible and motion blur becomes a problem when photographing moving objects. |
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