> If you are limited by the film to be about 100 lp/mm resolution when
> in fact most 35mm lenses are far above this, then why are ANY lenses
> quoted as having less than 100 lp/mm resolution? Look at some of the
> numbers in the Web pages linked to Lee Hawkins Web site. Some lenses
> wide open are down around 50 lp/mm. This doesn't seem to make sense.
It makes perfect sense. In such lenses, the aberrations are so severe
that they dominate the factors affecting the lens's resolution.
You are also overlooking the fact that the net resolution of film+lens
is determined by the resolution of _both_. For example, if the lens has
a resolution of 100 lp/mm and the film is 100 lp/mm, then the effective
resolution is about 50 lp/mm. Doubling the film's resolution to 200
lp/mm would produce a net resolution of about 66 lp/mm, a noticeable
improvement.
The approximate net resolution is found by taking the inverse of the
lens's and film's resolutions, adding the inverses, then taking the
inverse of the sum (like two resistors in parallel, if you want an
electrical analogy). _Both_ resolutions limit the net resolution, and
improving either improves the total.
> The SYSTEM resolution (let's say in the case of slides) is a function of
> both the lens and film resolution.
Correct...
> If you have film resolution of around 100 lp/mm but have a diffraction-
> limited lens of around 500 lp/mm (or whatever) then the resulting image
> will have a resolution of around 98 lp/mm or something like that. Thus
> you are limited by the coarser resolution component, be it lens or film,
> which of course makes sense.
No. You stated it correctly in the first sentence, then said exactly the
opposite.
The net resolution in this case is about 80 lp/mm. Although the lens has
five times the resolution of the film, its "contribution" nevertheless
reduces the net resolution by 20% -- a difference that might be
noticeable in a big enlargement.
The point is that _both_ resolutions affect the final result. The
"coarser" component _does not_ "wipe out" the degradation introduced by
the "finer" component. Unless the lens or film are Really Terrible,
improving either will always improve the final result.
>>>>
One other point. As a tech writer, I am unduly fussy about words and
their use. But I can't let a misspelling like "brossure" pass without
comment.
The word is spelled "brochure."
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