Tammy 17 - 50mm F2.8

Started Feb 10, 2009 | Discussions thread
Gene L.
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Diffraction degradation is affected by sensor size
In reply to Larry MacKinnon, Feb 19, 2009

The curvature of the microlenses will affect light rays hitting at more extreme angles, which would be at the edges of the sensor. So microlens curvature can cause darkened edges (vignetting) because some of the light does not get directed to the sensor's photosite. This effect tends to be more pronounced with full-frame sensors because the light at the edges is projected at a more severe angle than for the edges of an APS sized sensor. film of course does not suffer this effect because it is essentially flat.

Diffraction degrades IQ for smaller sensor sizes at a larger aperture because of the sensor's size, not because it is digital. APS sized film will have the exact same effect from diffraction as an APS sized digital sensor.

The effect from diffraction factors in the same way as the circle of confusion factors in to depth of field. In both cases the unfocused light influences the image projected onto the sensor/film. An APS sized sensor is affected to a greater extent compared to full-frame because of the smaller sensor. The out of focus light from diffraction/DOF, is a greater percentage of the sensor's area, assuming all else is equal. That is same lens, same aperture, same subject, same focus point.

-Gene L.
http://www.ttl-biz.com

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