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06-05-2016, 10:47 AM   #1
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Pentax-M 100mm f/2.8 vs Pentax-A 100mm f/2.8

I was wondering if there's any difference between the Pentax-A and Pentax-M 100mm f/2.8 (non-macro) optically. I know the A has automatic aperture, but I'm wondering if there's a difference in the optics, since one is half the price of the other. Thanks!

06-05-2016, 11:01 AM   #2
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SMC Pentax-A 100mm F2.8 Reviews - A Prime Lenses - Pentax Lens Reviews & Lens Database
SMC Pentax-M 100mm F2.8 Reviews - M Prime Lenses - Pentax Lens Reviews & Lens Database

Both have 5 elements in 5 groups which is not definitive, but does indicate a strong likelihood they are the same.
06-05-2016, 11:06 AM   #3
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bdmitrov uses the same optical diagram for both.
http://kmp.bdimitrov.de/lenses/primes/_optics/100f2.8.gif
OTOH his photos of the two lenses show a slight difference in the IR but that might not be real.
06-05-2016, 11:08 AM   #4
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Haven't tried the A version, but I can say that the M is great! I realize that this doesn't answer the question... But if you're worried that the M is optically deficient, I think all would agree that it isn't! According to the DB, "This lens is optically similar to its M version." I think the high price is just for the auto aperture....

06-05-2016, 11:35 AM   #5
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Great, thanks for all the replies! I think I'll go with the considerably less expensive Pentax-M version. Thanks!
06-05-2016, 12:26 PM   #6
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Yep, good choice, one of my favorite from the M series.
It has a nice smooth transition between iF and OoF areas, and bokeh is buttery smooth.
06-05-2016, 02:29 PM   #7
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I owned the M briefly, and currently own the A. They have the same optical formula. I'd really consider getting the A version. In-body aperture adjustment and automated matrix metering are a HUGE step forward as opposed to the aperture ring and green button. The latter is fine if you're shooting landscapes on a tripod, but I take pics of people and pets with the 100 and the 'A' features are a godsend. Just my 2 cents.
06-05-2016, 03:08 PM   #8
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My understanding is that optically they are the same but the coating is different.

06-06-2016, 08:38 AM   #9
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QuoteOriginally posted by petrichordesign Quote
Great, thanks for all the replies! I think I'll go with the considerably less expensive Pentax-M version. Thanks!
Personally I would skip both the 100mm f2.8 lenses and go with the K105/2.8. It will be the sharpest of the bunch, better built and better handling.

Phil.
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