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Old Sep 17, 2008, 7:08 AM   #1
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One of my most-used lenses is a Pentax SMC 50mm f/1.4 that I bought new in about 1976. It has been superceded by similar Pentax lenses bearing appelations suc as "M", "A", "F", "FA", etc. It was preceded by "Takumar" lenses, possibly of several types. This lens is almost as new, regardless of its age, and, since it is kind of an old buddy, I will keep it in any case.

My question: are the optics in all of these essentially the same? If not, what is considered to be better? I am used to shooting manually. I might replace the lens I now have if I can get an alike one which is greatly better.

I hope someone reading this has had experience enough in this matter to asdvise me.

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Old Sep 17, 2008, 11:11 AM   #2
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As far as I know, and can see on Bojidar Dimitrov's fantastic site http://www.bdimitrov.de/kmp/ the optical design of all Pentax 50mm 1.4 (K, M, A, F, FA) is the same. But apparently there was some tweaking of the lens elements when the A version was introduced, to get (even) better resolution in the corners. This should be of less importance when used on a digital body, due to the smaller sensor. Maybe there is a difference/improvmentin the SMCcoating. Some say one is better, some say another. Myself I think differences are rather due to the individual lens or batch of lenses.

For a thorough discussion on the topic, check Stan's page: http://stans-photography.info/. Click "normal prime lenses", scroll to "50 mm Lenses - They are all good; which is better", click the headline to get the extended discussion. Then enjoy the reading, after that you will enjoy and appreciate your recent lens even more.

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Old Sep 17, 2008, 2:34 PM   #3
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An interesting question. My own personal experience is that my M 50mm 1.4 lens is really soft at 1.4, softer than my M 50mmm 1.7 is at 1.7. If you stop both lenses down to f2, they are exactly the same. It's seemed to me that the pictures posted around here taken with either the A or FA versions of the 1.4 are better than what my M 1.4 is capable of, so I always assumed that Pentax tweaked the design when they came out with the A version, making it sharper wide open. But Kjell is probably right - my softness could be due to the particular lens I happen to have, rather than a design change.
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Old Sep 17, 2008, 7:34 PM   #4
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i've used both the M and the FA and i have to say that i miss my M even tho it was perfectly usable(i've got great shots) wide open i've got to say the FA is a tad bit better IQ and is AF to boot.. it's one of 2 AF lenses i have out of 11 i use..

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