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Diffraction blur with the R5 and four prime lenses

Started 7 months ago | Discussions thread
Sittatunga Veteran Member • Posts: 5,406
Re: Ran "Find Edges" - F1.2 Primes consistent with zoom lenses in terms of F-number and diffraction
3

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.

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