MP Resolution of 35mm Film?

Started 3 months ago | Discussions thread
alanr0 Senior Member • Posts: 2,234
Re: Lens resolution - reference wavelength

A Marcus wrote:

@alano --- As you know, the Rayleigh Criterion is universally accepted. The lines per millimeter limit is a variable based on wavelength.

Sure. It is not the only resolution criterion, but it is very widely used.

Photographically 1392 millimicrons is based on the visual focus of person working with a ground-glass image and a loupe. Films have a different chemical focus based on type.

I am not clear what you mean, or how this relates to lens resolution.

For a diffraction-limited lens, the Rayleigh criterion at wavelength λ and f-number N corresponds to a resolution at 9% contrast of a spatial frequency of 1/(1.22 λ N)

1392 cycles per mm is equal to 1/(1.22 x 0.000589) = 1/(1.22 λ) when the wavelength, λ, is 589 nm.

This has nothing to do with ground glass.

I questioned why you chose 589 nm, which is yellow/orange and not green. Presumably either the sodium D doublet, or perhaps the zinc 589.44 nm emission line?

As far as I can tell, it is far more common to specify lens resolution at a green wavelength near 550 nm, where the eye is most sensitive, or at a slightly shorter wavelength such as 500 nm or 520 nm.

Not a big deal. I was simply curious why you thought [resolution] "varies with wavelength but it is generally stated for green wavelength 589 millimicrons".  589 nm seemed an odd choice.


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Alan Robinson

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