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10-20-2010, 10:52 AM   #1
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Pentax-A 50mm 1.7 vs Pentax-F 50mm 1.7

I recently picked up a Pentax-F 50mm 1.7 to replace my Pentax-A 50mm 1.7 because I found I use the 50 1.7 quite often and wanted the convenience of auto-focus. By the way, I got an amazing deal on the F 50mm at a local camera shop that carries used lenses. No one in my town uses Pentax apparently as everywhere I go Pentax lenses are very cheap and have been sitting on the shelf for ages.

Anyway, so I picked this up and thought, before I sell the A 50 I should compare it to the F 50. I was a little surprised after comparing the pics as I thought these were Identical lenses in all aspects with exception of the Auto Focus and computer connection. The A 50 seems to render reds a little truer then the F 50. Using the F 50 the red come out slightly purpleish or pinkish, while the A 50 renders true reds. The difference is very minimal but noticable when looking at the images side by side. I compared the shots to the subject and indeed the A 50 seems to be closer to the real color. Has anyone else seen this kind of thing? Is it that the camera, recognizing the exact lens it is, makes adjustments to the color that i'm not aware of? Is there aything I can do, an adjustment in the camera settings, that will bring the color back into line? Just to be clear, I shot both lenses using the same iso, shutter speed, aperture, etc. All Identical even in the EXIF data. Oh by the way, I use a K-X.

Any thoughts?

10-20-2010, 11:33 AM   #2
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Did you use the same white balance as well?
10-20-2010, 02:54 PM   #3
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I didn't mess with it. Is that something that the camera might automatically change? I honestly have not had a lot of time to wade through the huge manual to find out every little detail about the camera.
10-20-2010, 04:11 PM   #4
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QuoteOriginally posted by Damian Quote
No one in my town uses Pentax apparently as everywhere I go Pentax lenses are very cheap
And what town might this be?. Just asking.

10-20-2010, 04:31 PM   #5
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I have experienced with the A50 f1,4 and the F50 f1,7 (and the FA50 macro and the M50 f2...) and I think the culprit is the coatings, mainly. White balance might affect the output, but only because light is affected differently by the different lenses. It's normal, as long as it's not obvious (and you say you only see it when comparing, so I'd call that normal).
10-20-2010, 04:44 PM   #6
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White Balance

QuoteOriginally posted by Damian Quote
I didn't mess with it. Is that something that the camera might automatically change? I honestly have not had a lot of time to wade through the huge manual to find out every little detail about the camera.
White Balance is only a "little" detail if you also didn't care about what film you used back in the '36 exposures at a time' days. For lens comparisons it would pay to set the white balance to something other than Auto. I don't have a Kx but I'm guessing you will access these settings through a function (Fn) button while in shooting mode.

Coatings on your lenses might be different or have changed with age. These could cause the auto white balance to compensate differently.

Loads of users used to complain about the auto white balance on earlier Pentax dslr's, but I thought it was pretty good. On my K10/20d's the camera seems to assume daylight, unless there is a consistent colour cast across the image.

And... Don't forget to add your observations to the lens review database, even for commonly reviewed lenses like the fast fifties.

Last edited by Matthew; 10-20-2010 at 05:46 PM.
10-20-2010, 07:42 PM   #7
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Oh believe me Matthew, I'm slowly adding my reviews to the lens review section as I test my lenses. Part of the reason for this thread is to get more information regarding the results I'm getting so I can accurately review the lenses.

I guess the difference could be in the coatings. It just seems odd to me though, looking at the glass of both lenses, the coatings look identical. You know, the little reflected light bulbs you see when holding it under a light, they look the same in both. I know that different coatings look different in the reflection, so unless it's a very minor difference I don't see how it could be the coatings. But again, it is a very minor difference in the images so I guess it could be the coatings. The diifference is so minor that if I wasn't comparing the images side by side I probably would never have noticed any difference at all.

Thanks for the tip on the white balance. I was unaware that it was even set to auto. which after checking the EXIF data and the camera settings, is probably where the discrepancy is coming from.

Thanks for your help everyone. This has prompted me to learn something about my camera that I thought was best left alone. If not for your insight, I would have continued taking pictures without ever considering the effect of white balance. I'm going to mess with that a bit and see how the two lenses compare. If there is still a difference, maybe it's the coatings.

Ex Finn, to answer your question, Pensacola Florida. You are too late though, we only have two camera stores and I've already picked the best lenses from both. The one down town still has a nice Pentax-M 50mm 1.4 that I might decide to get, but I don't see much of a point in that since I have a 1.7.... actually two 1.7's right this second. I've scrounged most of the pawn shops as well. Nothing there. Thus far the best deals have been from the flea market. But I haven't gone back there in a while. I might have to go check it out again and see if there are any new gems to rescue.

Last edited by Damian; 10-20-2010 at 07:49 PM.
10-20-2010, 07:58 PM   #8
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My F 50/1.7 always seemed a little different in color to me compared to other lenses. More blue or cyan than I expected. I used to fix it in PP. But now with a K20 I see you can tweak WB, even auto WB, and I am sure that would do it too. Not sure if that will work with the K-X.

If there is an M 50/1.4 sitting out, all the good lenses have NOT been taken. Maybe the wife wants to go to FLA for a bit this fall... :-)

10-20-2010, 08:06 PM   #9
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Come on down, our beaches are oil free but no one knows that since the news doesn't cover stories like that. Regardless, we need all the tourists we can get after this past summer. I'll even take you to the flea market where I found the Pentax-A 135mm/2.8 in excellent condition for $30. Maybe you can find a gem of your own.
10-21-2010, 12:09 AM   #10
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Your experience would confirm mine...
I used to have F50/1.7 and it was much cooler than your average SMC lens. So yes, the reds were not as red, on the other side, I rather enjoyed that rendering and found it very useful for portraits where I wanted colder skin tones....
10-21-2010, 12:34 AM   #11
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I used to have these lenses when I was shooting film. What I have found with digital is that there is no such thing as accurate colour. Each camera model is different, light quality makes the difference, and then there is WB setting, RAW camera calibration. Even with identical setting and WB, a few cont shots will produce slightly different colour. And then there is monitor calibration which varies greatly between monitors and calibration devices even of the same model. I do my best on camera & monitor calibration once then leave them behind. If I demanded absolute colour accuracy, I would be insane in no time (maybe I already am).

Last edited by wlachan; 10-21-2010 at 06:23 AM.
10-21-2010, 02:14 AM   #12
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Whether my Sony | Minolta | Olympus P&S's, or my K20D, I find I nearly always must adjust WB and/or use a REMOVE COLOR CAST tool in PP. Exactitude is beyond me, so I just don't sweat any fractional tonal differences between similar lenses. Those differences will be swamped-out during PP. If your photos MUST be totally accurate, try a manual adjustment of WB -- fine-tune it.
10-21-2010, 06:13 AM   #13
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QuoteQuote:
the coatings look identical. You know, the little reflected light bulbs you see when holding it under a light, they look the same in both. I know that different coatings look different in the reflection, so unless it's a very minor difference I don't see how it could be the coatings.
Comparing how coatings look cannot be taken as a criteria to evaluate if they are identical, sorry. They are designed to do the same thing (let more light pass through) so they should all look pretty similar. But underneath they can be vastly different. And often will be.
10-21-2010, 09:36 AM   #14
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QuoteOriginally posted by bdery Quote
Comparing how coatings look cannot be taken as a criteria to evaluate if they are identical, sorry. They are designed to do the same thing (let more light pass through) so they should all look pretty similar. But underneath they can be vastly different. And often will be.

No problem, I was just stating an observation more then anything.
10-21-2010, 09:45 AM   #15
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I went a little further yesterday in my testing and took pictures of the same subject under the same light with 2 other lenses. A Pentax-a 35-05 and a Miranda 24mm 2.8 macro. Surprisingly the color rendering of those two are almost identical to the F 50/1.7. I'm right back to square one. the fact that all three have almost the same color is perplexing. Basically, I'm starting to wonder if the difference is simply the lens. I've decided I'm going to retest all lenses involved, with identical settings, and mess with the white balance and see what I can come up with.
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