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Diffraction blur with the R5 and four prime lenses

Started 7 months ago | Discussions thread
Karl_Guttag Senior Member • Posts: 1,883
Re: Ran "Find Edges" - F1.2 Primes consistent with zoom lenses in terms of F-number and diffraction
1

Sittatunga wrote:

Karl_Guttag wrote:

...

A bit of a surprise for me in the whole process of checking many lenses I have tested is the consistency with which the diffraction is a function of f-number (a ratio) and not the absolute dimension of the aperture regardless of the focal length or lens quality.

That's what the mathematics predict. The angular size of the Airy Disc for a circular aperture is 1.22λ/d in radians, where λ is the wavelength and d is the diameter of the aperture. For a lens focal length f, focussed at infinity the size of the Airy Disk will be f(1.22λ/d). But (from the definition of the f-number) at any f-number n, d =f/n, so the size of the Airy Disk on the sensor will be f(1.22λ/(f/n). The fs cancel out, leaving it as 1.22λn, a constant multiple of the f-number.

Thanks for breaking down the math. Nice that math agrees with the experimental results. The experimental results show at what f-number with an R5's sensor the diffraction becomes significant.

I had read for years that a perfect lens would be the sharpest wide open due to diffraction. I was surprised that the diffraction losses were barely visible even with a 45MP sensor until f8. Also, f11 is only slightly worse than f8, and it was not until f16 that the diffraction became significant.

 Karl_Guttag's gear list:Karl_Guttag's gear list
Canon EOS R5 Canon RF 15-35mm F2.8L IS USM Canon RF 24-70mm F2.8L IS USM Canon RF 70-200mm F2.8L IS USM Canon RF 24-240mm F4-6.3 +14 more
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