At 20:06 26.09.01, Bernd Moeller wrote:
But isn't there a connection between grain and resolution? What do both
parameters mean for the average photographer or for projecting slides?
Of course there's a connection between the two, but it's not a one-to-one
relationship. I'm no expert on the chemical processes in film, but I would
imagine that resolution also depends on how large contrast two neighboring
grains can have.
Taking one grain and divide it in four smaller grains would not give you
any more resolution if the four grains still had the same tonal value and
placement, this is in fact a bit like the simplest form of digital
upsamling. If the four grains where a bit randomly placed (not like pixels)
it would look smoother and more pleasing to the eye, but that has little or
nothing to do with the amount of information the film can hold.
Further, even the very best lenses will max out at about 100lp per mm. If
we assume that resolution limits in film and optics are caused by (randomly
distributed) noise, we can estimate the resolution for the system
film+optics (150lp+100lp):
1/ Final resolution = sqrt( 1/[100*100] + 1/[150*150] ) = sqrt(0.00014) =
0.0120
Final resolution = 1/ 0.0120 = 83, that's 83lp per mm.
That should be a *very* optimistic value for what's possible with colour
film. If you substitute more realistic values for film resolution and
optics resolution (for normal low contrast subjects with normal optics, for
instance) you'll probably be depressed. But the picture still looks good on
the wall.
You can also see for yourself how much difference to expect from two films
with the same mediocre lens, or a super-duper lens hand held. You'll either
be obsessed with tripods, or stop caring about resolution numbers in films.
My point? The difference between modern films are saturation and contrast
(and grain if you choose from a wide range of speeds), resolution is pure
marketing.
Regards,
Thomas Bryhn
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