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03-10-2011, 07:19 PM   #16
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Bojidar Dimitrov's Pentax K-Mount page has a nice presentation of lens information, including which lenses share optical formulas.

03-10-2011, 11:01 PM   #17
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Another interesting set is the A/M 200mm f/4 lenses. It appears they added a lens group and slightly shortened the minimum focusing distance, while keeping the same general body dimensions. I've only ever used the A version, so I can't say how they compare optically.
03-11-2011, 10:36 AM   #18
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Even when A lenses share the same optical formula, it appears that they may be sharper. Consider these resolution tests of A and M lenses in the normal range. The A versions tend to be sharper at most apertures than the M versions; which suggests that Pentax tweaked them to get better performance.
03-11-2011, 12:47 PM   #19
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is this really true ?? the A version is much sharp and better then M ??
i thought , the difference is just A contact in K-Mount, which is the Aperture (Av) Mode can be use in modern DSLR ..

03-11-2011, 01:02 PM   #20
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Ah, resolution tests. I love tests, just as I love standards, because so many exist.

What the cited tests don't indicate: Is there more copy variation than version variation?

The acid test: In any user's normal (non-pixel-peeping) day, will they notice a difference?
03-11-2011, 04:31 PM   #21
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Biggest downside to me of M lenses is that aperture is not recorded in EXIF.
03-11-2011, 04:50 PM   #22
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I suppose there could have been minor improvements in manufacturing tolerances, coatings and such over the years and so A lenses even with the same optical formula could be slightly better?
03-11-2011, 05:45 PM   #23
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QuoteOriginally posted by RioRico Quote
Ah, resolution tests. I love tests, just as I love standards, because so many exist.

What the cited tests don't indicate: Is there more copy variation than version variation?

The acid test: In any user's normal (non-pixel-peeping) day, will they notice a difference?
Actually, many of those test results could be within copy variation and variations in testing.

03-12-2011, 08:15 AM   #24
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Also in movie mode, lens set at A setting has accurate exposure than without A setting.
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