A versus M lenses

thirdofthree · 03-10-2011, 07:19 PM

Bojidar Dimitrov's Pentax K-Mount page has a nice presentation of lens information, including which lenses share optical formulas.

Rykoh · 03-10-2011, 11:01 PM

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.

northcoastgreg · 03-11-2011, 10:36 AM

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.

ewig · 03-11-2011, 12:47 PM

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 ..

RioRico · 03-11-2011, 01:02 PM

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?

sewebster · 03-11-2011, 04:31 PM

Biggest downside to me of M lenses is that aperture is not recorded in EXIF.

jolepp · 03-11-2011, 04:50 PM

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?

GeneV · 03-11-2011, 05:45 PM

Originally posted by RioRico

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.

liukaitc · 03-12-2011, 08:15 AM

Also in movie mode, lens set at A setting has accurate exposure than without A setting.

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03-10-2011, 07:19 PM	#16
thirdofthree Senior Member Join Date: Mar 2008 Location: Highland Park, IL Posts: 217	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
Rykoh Veteran Member Join Date: Aug 2007 Location: Oregon, USA Posts: 318	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
northcoastgreg Pentaxian Join Date: Feb 2010 Location: Northern Michigan Photos: Gallery \| Albums Posts: 6,173	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
ewig Veteran Member Join Date: Jan 2010 Photos: Albums Posts: 312	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
RioRico Veteran Member Join Date: Jun 2008 Location: Limbo, California Posts: 11,263	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
sewebster Veteran Member Join Date: Jun 2008 Location: Vancouver, BC Photos: Gallery Posts: 544	Biggest downside to me of M lenses is that aperture is not recorded in EXIF.

03-11-2011, 04:50 PM	#22
jolepp Veteran Member Join Date: Oct 2010 Location: Finland Photos: Albums Posts: 3,196	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
GeneV Veteran Member Join Date: Oct 2008 Location: Albuquerque NM Photos: Albums Posts: 9,830	Originally posted by RioRico 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
liukaitc Veteran Member Join Date: Jul 2010 Location: New York Photos: Albums Posts: 1,008	Also in movie mode, lens set at A setting has accurate exposure than without A setting.