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jcolwell
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Re: 100-400ii + 2xiii: usable?


rabbitmountain wrote:
Thanks for that . Isn\'t diffraction due to the light passing through only the extreme centre area of the lens?.


No. It\'s more or less the opposite of that.

Diffraction happens when light (and ocean waves) pass by an edge (in which case, the light at and very near to the edge bends) or through a small hole (after which, the light spreads). When a lens aperture is wide open, you get diffration (bending of waves) all around the outer edge of the optics, but it\'s a very small proportion of the total amount of light entering the lens (i.e. the diffracted light rays are only those at and very close to the edge, while almost all of the light passes into the lens without getting close enough to an edge to get diffracted. When you stop down the lens, the amount of light diffracted (bent) at the edges of the aperture becomes a much larger proportion of the total light entering the lens, and so a much greater proportion of the image is affected (usually by blurring), by the diffraction.




Oct 25, 2016 at 03:09 PM





  Previous versions of jcolwell's message #13778597 « 100-400ii + 2xiii: usable? »

 




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