MP Resolution of 35mm Film?

Started 3 months ago | Discussions thread
Trebor1 Regular Member • Posts: 193
Re: Lens resolution - reference wavelength

alanr0 wrote:

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.

Peak sensitivity in the human visual system is at 555 nm, in normal to bright light but this shifts to 550 nm in lower but not Scotopic levels, such as found in an inspection booth for testing materials, using fluorescent penetrative inspection, at this wavelength.

Regarding the 589 nm wavelength used by A Marcus, for lens resolution: This is a fluorescence peak wavelength, in microscopy/biological applications: DyLight 549 555 nm (excitation) 569 nm emission but there are several other fluorescent dyes also in the 567-570 nm region but otherwise not particularly significant?

There are considerably greater number of the Long wavelength 'Red' sensitive cone cells present , in the human visual system, in the central fovea 2:1 relative to the Medium 'Green' with only 2% sensitive to short wavelengths 'Blue'. There are also rods (Purple-Blue-Green sensitive) in the 1.2 mm diameter fovea but not within the central high-resolution 0.3 mm foveola.

looking at the cone responses in the link above and particularly the ratio of Long to Medium cones, would it be reasonable to slightly shift the wavelength, used for lens diffraction/resolution calculations, towards the Long wavelength cone peak of 575 nm, for Human vision at least, although digital cameras using various Bayer CFAs are a different matter?

Going a bit off-topic: it is interesting that most of the short-wavelength receptive 'Blue' cones are actually not in the fovea and that resolution, in humans, for this region of the visual spectrum, is relatively poor ie. visual acuity falls by 75% at only 6 degrees off-centre! This matches well with the improved performance of the 10-degree 1964 CIE obsever, with colour matching, relative to the 2-degree case. OTOH, it doesn't seem to be well represented by the Bayer CFA, which more sparsely samples both blue and red, whereas the HVS is significantly lower resolution, only in the blue?

The eye also has a different type of photoreceptor, in addition to cones and rods, in the form of intrinsically-photosensitive retinal-ganglion cells. These are Blue sensitive and may play a role in human vision, including adaptation to light levels and possibly chromatic adaptation? They are most sensitive to light at around 480 nm (Berson, 2002; Dacey, 2005; Tu, 2005), significantly different (≥20 nm) from the best wavelengths for stimulating rods and cones

" In addition, there is emerging evidence that melanopsin contributes to visual perception, which is probably mediated by ipRGC projection to the LGN and/or SC (Dacey, 2005; Brown, 2010; Ecker, 2010; Estevez, 2012; Zhao, 2014). Some blind patients with severe outer retinal degeneration but relatively normal ipRGCs possess a rudimentary ability to detect the presence of intense blue light (Zaidi, 2007), and fully sighted humans as well as mice appear to depend partly on melanopsin for brightness discrimination (Brown, 2012). Mice lacking rod/cone photoreception (but with intact melanopsin photoreception) were able to distinguish a computer screen displaying black and white stripes from a uniform gray screen of an equal mean intensity, suggesting melanopsin is sufficient for a certain degree of pattern vision (Ecker, 2010). There is also preliminary psychophysical evidence that melanopsin directly contributes to color vision in humans, challenging the trichromatic theory (Horiguchi, 2013). Most recently, mice lacking melanopsin were shown to have behavioral deficits in contrast sensitivity (Schmidt, 2014).

IpRGCs are likely to perform additional image-forming visual functions because under conditions preserving synaptic input, primate ipRGCs receive color-opponent (blue OFF, yellow ON) input from cones (Figure 21B), implicating a capacity for color discrimination (Dacey, 2005)."

So perhaps digital cameras should have a 5 colour CFA, in order to better match the human visual system?


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