There's an interesting essay on resolution at Luminous-Landscape which
summarizes a lot I've read on resolution limits and puts it all
together. The bottom line is to cling to those middle apertures for the
best resolving power since diffraction gets you on the small end and
numerous other abberations (chroma, coma, etc) get you on the large end.
Of particular interest is the maximum number of pixels that can be
resolved with a theoretically perfect lens for various sensor formats.
For 35mm size sensors like the 5D even a diffraction limited lens can't
do better than 16 MP at f/11. Shooting at f/16 takes it down to only 7
MP. f/8 can theoretically deliver 29 MP but it would take a mighty fine
lens to go with that mighty big pixel count.
As you move down in sensor size you must also use wider apertures to
maintain sufficient resolution for those tiny pixels. With an APS-C
size sensor (most of them) you've got to stay at f/8 to achieve a
theoretical maximum of 13 MP. With a 4/3 size sensor you've got to
shoot at about f/5.6. The limit for f/5.6 is 17 MP but the limit for
f/8 is only 8 MP. For a 10 MP E-3 or E-4xx/5xx that means that shooting
at f/8 or smaller is giving you less resolution than what's possible
with an E-330.
The following is a rather long and detailed article so you might want to
skip directly to Table 3 near the bottom of the page. Also note that
the resolution limits are only for yellow-green light at 555 microns.
Your lens will deliver even worse performance at the red and blue ends
of the spectrum. While not listed in the table, I conclude that the
resolution limit for my 5 MP Minolta A1 probably occurs at about f/4.
It also explains DP Review's comment when testing the 8 MP Minolta A2
(that uses the same lens) that the sensor out-resolved the lens.
See: <http://www.luminous-landscape.com/tutorials/resolution.shtml>
Chuck Norcutt
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