Diffraction Limit

Started Aug 28, 2013 | Discussions thread
GeorgianBay1939
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Re: Diffraction Effects in a Real Lens-Camera System
In reply to s_grins, Aug 28, 2013

s_grins wrote:

Tom, I suspect that other sources call this low dispersion glass, where refraction (+) and refraction (-) compensate each other for some degree. But this is my guess, and I can be damn wrong

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Looking for equilibrium...

Low dispersion glass is a glass where the index of refraction doesn't change much with wavelength (colour) so that the bending of the light through the glass is (approximately) the same for all colours.  But there is no "zero dispersion" glass so there will always be some dispersion and consequently some Ca.

The Canon approach has this little sandwich, that I have the arrows pointing at, which seem to be little diffraction gratings, which serve to reverse the colours in an opposite way to normal refraction:

It would be interesting to hear how effective that approach is.  As everyone knows, lens design is always a compromise.  I wonder how this Diffractive Optics approach affects the other factors influencing lens "sharpness".

Lots to learn, eh?

t

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