Pentax-M 100mm f/2.8 vs Pentax-A 100mm f/2.8

petrichordesign · 06-05-2016, 10:47 AM

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!

**jatrax** · 06-05-2016, 11:01 AM

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.

aoeu · 06-05-2016, 11:06 AM

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.

gdneil · 06-05-2016, 11:08 AM

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....

petrichordesign · 06-05-2016, 11:35 AM

Great, thanks for all the replies! I think I'll go with the considerably less expensive Pentax-M version. Thanks!

LensBeginner · 06-05-2016, 12:26 PM

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.

Fat Albert · 06-05-2016, 02:29 PM

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.

Cuthbert · 06-05-2016, 03:08 PM

My understanding is that optically they are the same but the coating is different.

**gofour3** · 06-06-2016, 08:38 AM

Originally posted by petrichordesign

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.

06-05-2016, 10:47 AM	#1
petrichordesign New Member Join Date: May 2014 Location: NYC Posts: 5	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!

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06-05-2016, 11:01 AM	#2
jatrax Site Supporter Join Date: May 2010 Location: Washington Cascades Photos: Gallery \| Albums Posts: 12,991	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
aoeu Veteran Member Join Date: Sep 2010 Location: Oregon Posts: 496	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
gdneil Veteran Member Join Date: Mar 2013 Location: Yukon Posts: 516	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
petrichordesign New Member Join Date: May 2014 Location: NYC Posts: 5 Original Poster	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
LensBeginner Veteran Member Join Date: Sep 2014 Photos: Albums Posts: 4,696	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
Fat Albert Veteran Member Join Date: Jul 2013 Posts: 966	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
Cuthbert Veteran Member Join Date: Nov 2013 Photos: Gallery Posts: 1,740	My understanding is that optically they are the same but the coating is different.

06-06-2016, 08:38 AM	#9
gofour3 Site Supporter Join Date: Oct 2008 Location: Vancouver, Canada Posts: 8,091	Originally posted by petrichordesign 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.