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05-29-2009, 10:11 AM   #1
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IQ difference between 'SMC' and 'smc' version of 50/1.2

Hi,

Is there any real/significant image quality difference between the 'SMC' and 'smc' version of the pentax 50/1.2 at wide open f-stop?

Specifically, has anyone seen test shots from both lens for the same subject at identical lighting condition.

Thanks for your time and comments

Cheers

05-29-2009, 10:28 AM   #2
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QuoteOriginally posted by cheve Quote
Hi,

Is there any real/significant image quality difference between the 'SMC' and 'smc' version of the pentax 50/1.2 at wide open f-stop?

Specifically, has anyone seen test shots from both lens for the same subject at identical lighting condition.

Thanks for your time and comments

Cheers

Cheve, not sure what you meany by "smc" vs. SMC.

There are two Pentax 50 1.2's - the SMC or "K" version, and then the A 50 1.2.

Did you mean to ask about the comparison between those two? If so, aside from external cosmetics, looks like they both share the same optical design, according to Boris, Although the A has 9 aperture blades, and the K only 8.
05-29-2009, 10:37 AM   #3
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K 50/1.2

QuoteOriginally posted by cheve Quote
Hi,

Is there any real/significant image quality difference between the 'SMC' and 'smc' version of the pentax 50/1.2 at wide open f-stop?

Specifically, has anyone seen test shots from both lens for the same subject at identical lighting condition.

Thanks for your time and comments

Cheers
I once owned the SMC version. AFAIK the ONLY differences between the lower case and upper case version is the printing on the filter trim ring. From Boz's website:

smc version 1975-1977
SMC version 1977-1981

Then the "A" version started.

Bojidar Dimitrov's Pentax K-Mount Page - K 50/1.2
05-29-2009, 11:07 AM   #4
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thanks for your reply monochrome and jsherman999,

Out of the 3 'common' variations of 50/1.2

SMC Pentax
smc Pentax
smc Pentax-A

Just wonder, if anyone has test shots of them with the same subjects and lighting.

Cheers,

05-29-2009, 05:37 PM   #5
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those two lenses are basically identical, although the more current A series has 9 aperture blades instead of 8 and electrical contacts for transmitting aperture data to the camera.

but optically I don't think they are exactly the same, the older K version is slightly sharper in the corners than the A version is. It isn't a night/day difference but it's there.
05-29-2009, 06:32 PM   #6
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QuoteQuote:
but optically I don't think they are exactly the same, the older K version is slightly sharper in the corners than the A version is. It isn't a night/day difference but it's there.
I would disagree. Although based on small sample size, I found the only significant resolution difference between the K 50/1.2 and the A 50/1.2 to be corner resolution, and in favor of the A model - SMC Pentax Resolution Test Results

I also thought, subjectively speaking, that, similar to some other K and A siblings, the A 50/1.2 had a slightly higher contrast than the K 50/1.2, as well.

The above comparisons were made by me a number of years ago, back in the film days when I used manual exposure and aperture-priority exposure for everything, and it did not matter to me if I sold the K's to keep the A just for the Ka functionality - instead, I chose the A (which I still have) for its slightly better optics (and, in fact, took this as enough of an advantage to compensate for the fact that the K lenses had a slightly better focus feel.

Please note that I cannot say that all A 50/1.2's are a smidge better than all K 50/1.2's, but only that my A was better than my K's.
05-29-2009, 06:57 PM   #7
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QuoteOriginally posted by fwcetus Quote
Please note that I cannot say that all A 50/1.2's are a smidge better than all K 50/1.2's, but only that my A was better than my K's.
They both have the same optical formula.


The difference in measurement could also be due to Random error - Wikipedia, the free encyclopedia,
Systematic error - Wikipedia, the free encyclopedia, or one of
List of cognitive biases - Wikipedia, the free encyclopedia
not necessarily due to any difference in the samples themselves--although, this is also possible.
05-29-2009, 07:04 PM   #8
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QuoteOriginally posted by asdf Quote
They both have the same optical formula.
But that does not mean they are necessarily the same - the exact shapes and the exact locations of the lens elements and groups can be subtly modified to make performance (such as resolution at the corners) better (or worse).

Lens coatings can also be changed (although this would probably affect contrast more than anything).

05-29-2009, 07:15 PM   #9
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QuoteOriginally posted by fwcetus Quote
But that does not mean they are necessarily the same - the exact shapes and the exact locations of the lens elements and groups can be subtly modified to make performance (such as resolution at the corners) better (or worse).

Lens coatings can also be changed (although this would probably affect contrast more than anything).
Sure, and there can be difference in quality control, etc.

I'm just pointing out what is rarely mentioned for the benefit of the lurkers. A mark of a pseudoscientist is to never consider human error and/or cognitive bias.
05-29-2009, 07:32 PM   #10
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QuoteOriginally posted by asdf Quote
Sure, and there can be difference in quality control, etc.
Of course. That had not been mentioned yet (I don't think) in this thread.

QuoteOriginally posted by asdf Quote
I'm just pointing out what is rarely mentioned for the benefit of the lurkers. A mark of a pseudoscientist is to never consider human error and/or cognitive bias.
I'll try to pretend (<g>) that you're not resorting to calling me a pseudoscientist.

If you look at my points in this thread, you should be able to see that I have not discussed random differences, quality control, or similar unavoidable variance factors - I don't think the OP was asking about such things.

In fact, when referring to my own previous resolution testing, I mentioned here that it was "based on small sample size" (2 K's and 1 A in the case of the 50/1's).

In discussing apparent contrast differences I said I was "subjectively speaking".

I also stated, "please note that I cannot say that all A 50/1.2's are a smidge better than all K 50/1.2's, but only that my A was better than my K's".

I do have to assume that the OP was interested in ~design~ differences between 50/1.2's, and not a discussion of quality control, biases, and human (and machine) errors.

We are not (or, at least, I am not) privy to what Pentax did or did not do differently when the K morphed into the A model. So, we have to go on what we can see - and I was responsively and responsibly adding to the thread what I had observed.

I read something that was contrary to what I had observed, so, "for the benefit of the lurkers" as much as anything else, I jumped in with a different set of observations.

Last edited by fwcetus; 05-29-2009 at 07:58 PM.
05-29-2009, 07:44 PM   #11
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PDML Commentary

you should go to the old Stan's Pentax Photography site and read the comments by PDML members on the differences between the K and A 50/1.2's. Click Normal Primes on the left and click 50mm f/1.2 in the main frame to get detailed comments on the K and A versions.

In my reading, although I have owned only the SMC K 50/1.2, the IQ differences are only meaningful wide-open, where the k versions are subject to softness and coma wings. f/8 - f/11 the lenses are all rated as very sharp, with the only real benefit of the speed found in low light FOCUSING for smaller-aperture shots.

I have never seen, nor read any mention of, any distinction between the two versions of the K lens. I believe the difference is merely cosmetic.
05-29-2009, 09:04 PM   #12
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on Stan's i think they've given the 1.2's a bad rap
05-29-2009, 09:16 PM   #13
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QuoteOriginally posted by k100d Quote
on Stan's i think they've given the 1.2's a bad rap
Yeah, I'm always pretty amazed when I read that section, although the argument that the speed isn't worth the extra money makes sense to me. Interesting that J. L. Colwell also rated all the 1.2's lower than all of the 1.4's and 1.7's except the M's.

He makes no distinction in the K 50's between the upper and lower case letters on the filter ring - they're not different versions of the K/1.2 - they are optically identical.

I owned my K50/1.2 for about a year. I sold it because I kept using the 1.4's and it just didn't make sense to have that much money sitting on the shelf doing nothing. I still have too many 50's, but I like to use lenses contemporary to the cameras I'm using - I just don't like an A50 on a KX or MESuper.
05-29-2009, 09:34 PM   #14
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asdf,

thank for the lens diagram. Your points on impact of sampling error, product variations and etc to our observation of the lens IQ is much appreciated. Unfortunately, I think it would be difficult to assemble a relatively large sample size(say n>25) from each version of 50/1.2 to run a suit of test and be able to express the result in certain degree of statistical confident level.

fwcetus,

thanks for the link to the resolution chart #, even though it was based on small sample, at least there are real # that I can sink my teeth into:-) Thank for sharing of your work experience with these two 50/1.2s.

Do you/anyone, by any chance, know how these numbers(of the 50/1.2) compare to say nikkon or canon's 50/1.2?

monochrome,

thanks for the link to Stan's website, the observations are valuable. However, the observations were mainly on comparing one of the 50/1.2 to a 50/1.4 and on how one would need to stop the said lens down to achieve max. sharpest. There was no direct comparison made between the 1.2.

Digitalis,

Thank you and appreciate your comments. Please do not take it in the wrong way, I just want to know that whether your observation was based personal work experience with the actual lens pair or was it formed based on information presented elsewhere?

I continue to believe that having identical shots of same subject from each lens under an identical lighting would give us a more balance and objective evaluation of these two 50/1.2

Thank you all for taking the time to enlighten me on this topic.

Cheers
05-29-2009, 10:49 PM   #15
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QuoteOriginally posted by cheve Quote
Do you/anyone, by any chance, know how these numbers(of the 50/1.2) compare to say nikkon or canon's 50/1.2?
No. Such resolution numbers (which certainly are ~not~ "absolution resolution numbers") are too dependent on individual testing tools and procedures. You couldn't even compare them to similar Pentax lenses tested by any other person. In fact, in this specific case, I would not even be able to test other lenses today and properly compare them to those results I obtained back in the 1990's.

"Apples and oranges"... <g>
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