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Message: <blockquote data-quote="Dave_W" data-source="post: 304420" data-attributes="member: 9521"><a href="http://www.gdanmitchell.com/2011/05/03/myth-diffraction-and-motion-blur-worsen-with-more-megapixels" target="_blank">Myth: Diffraction and Motion Blur Worsen With More Megapixels</a>The idea that diffraction blur increases as you increase photosite density (e.g.- use “more megapixels”) is rooted in the very same misunderstanding that I described in the original post – failing to take into consideration differences in the way that images are seen at 100% magnification on the screen versus how they are seen in real final images such as prints or on-screen jpgs. If you look for diffraction blur in a 100% magnification crop from a 21MP image on your computer screen and then look for it in a 100% crop from a 12MP image, the diffraction blur will appear to be “larger” in the first case than in the second.But it isn’t.Imagine some very gross diffraction in which (to use loose terminology) the “blur” from diffraction is 1% of the width of the frame. (This would be absolutely horrible blur, and it is far beyond what you’ll see in the real world – but 1% is a nice convenient value for this explanation.) Since the lens produces the blur, not the sensor, this “1% blur width” will be the same whether the image is projected onto a piece of 35mm film, a 8 MP full frame sensor, or a 21MP full frame sensor. In fact, for the thought experiment, imagine that you make photographs with all three media. Now make three prints at whatever size you prefer – let’s say 16″ x 24″ for the sake of having a real size in mind. The “1% blur width” will be 1% of 24″ in all three of the prints. In other words, there is no difference in the amount of diffraction among the prints due to different recording media or different photosite densities.The situation with motion blur is essentially the same. The crucial issue is over what portion of the image the blur takes place. If it is, say 1/10,000 of a frame width the blur will be 1/10,000 of the print width no matter what number of photosites you use – ignoring for a moment the fact that no current full frame DSLR can resolve 1/10,000 of the width of the frame. But let’s say the motion blur is grosser – perhaps 1/100 of the frame width. It will be 1/100 of the picture width in all three cases, independent of the film/sensor characteristics.</blockquote>

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