Joseph is correct that the table does not make sense, as long as film
resolution is fixed. Furthermore, the conclusion is correct that the system
resolution numbers will decrease as the lens is stopped down.
However, film resolution is not fixed. It too varies with lens aperture,
and inversely with lens resolution. The Gaussian error accumulation -
1/R = 1/Rf + 1/Rl - reasonably approximates this also, provided the
values for film resolution increase and the values for lens resolution
decrease through the lens' aperture range. My apology for not being more
clear in my earlier post.
John P
______________________________________
Joseph Albert <jalbert@xxxxxxx> remarked:
>this doesn't make sense. If you have a lens that is sufficiently
>well corrected to achieve its theoretical resolution at f/2.8, then
>it is only going to achieve its theoretical resolution at smaller
>apertures (which is lower as more diffraction) and so the system resolution
>numbers will decrease as the lens is stopped down. such a lens will
>be sharpest at f/2.8.
>
>Real lenses improve as the lens is stopped down because stopping down
>the aperture removes some aberrations thus getting sharper until
>the resolution is diffraction limited, and then the resolution
>starts decreasing as the lens is stopped down further.
>
>J. Albert
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