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07-16-2012, 09:46 PM   #16
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Yeah try what John suggested and use a faster shutter speed and f8.
I don't think it is the film, camera or scanning.
Try not to use a filter, to narrow it down to the lens only.

Phil.

07-16-2012, 10:09 PM - 1 Like   #17
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the first part of your post makes no sense. You answered your own question. As to the lens, eveyone here seems to forget or haven thought (especially the op) about the fact that we are talking about used vintage lenses, that have an unknown history. so blaming the an entire series for one lenses poor performance is just nonsense. The M 1.7, like virtually all pentax 50-55mm lenses gives excellent performance, even wide open. But then virtually all such lenses, no matter who manufactured them perform well, as they are all based on the same few basic optical formulas. If your particular example is performing poorly (or worse than you assume it should) and you are sure its not the film, the development, the camera or the scanner, then the lens is certainly to blame, but not all M series, or 1.7's or 50mm's. Just your lens.

Since we dont know the history of the lens, its hard to say. The most probable culprit is something like an element isnt in properly, or it wasnt reassmbled properly at some point. Such as an element put in backwards or something similar.

Last edited by séamuis; 07-16-2012 at 11:41 PM.
07-16-2012, 10:24 PM   #18
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At f8, an M50/1.7 will be near its best resolution and the equal of most lenses (including the 50/1.4). My first thought was that there was a focusing issue, but you seem to have ruled that out, so it seems to me that there's something wrong with your lens. Now, it's common enough for a mass-market zoom lens nowadays to have manufacturing defects which affect sharpness, but I think it would be very rare for an M-series lens. I think it's more likely that the lens has been damaged in some way - someone mentioned the rear element, and it's worth checking that out, as it's pretty sensitive to imperfections.

Also, try stopping down to f16: if there's an improvement in sharpness, there's definitely something wrong with the lens (assuming you've definitely ruled out the possibility of focusing error).
07-16-2012, 11:17 PM   #19
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why is everyone suggesting to stop down to f8 and even f16? What good would that do? If there is something physically wrong with the lens
to affect sharpness, it will be aparent at 1.7, but by f2 or f2.8, it willl be all but assured, and you can better rule out focusing issues at wider aperture. Stopping down to such apertures is not feasable for everyday use, and could help mask any issues that could genuinely be affecting the lens' performance. You should be testing for issues between 2 and 2.8 ideally.

07-17-2012, 12:50 PM   #20
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I'm pretty sure I mentioned in my post I shot both lenses at f/8. I was shooting with Portra 160 with my Pentax LX, at 1/75 (the sync speed, as it was hooked up to strobes).
07-22-2012, 04:18 PM   #21
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Tough to tell from the posted images. Of course you see less detail in the 50mm image - it is a shorter focal length and thus produces less magnification from the same distance. Plus we're viewing the images at different sizes. Add the very possibility that you missed focus, or that the lens is slightly out of whack - and I assume you have no image-degrading filters on it - bottom line, it's really impossible to say anything from that single comparison.
07-25-2012, 12:36 AM   #22
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QuoteOriginally posted by séamuis Quote
why is everyone suggesting to stop down to f8 and even f16? What good would that do?
I was suggesting f16 as a means of discovering whether there was a lens problem. The OP's original shot was taken at f8; if it's sharper at f16, then there's something wrong with the lens.
07-25-2012, 02:25 AM   #23
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QuoteOriginally posted by m42man Quote
I was suggesting f16 as a means of discovering whether there was a lens problem. The OP's original shot was taken at f8; if it's sharper at f16, then there's something wrong with the lens.
if its not sharp at f8, theres something wrong with the lens. if its not sharp by f2 theres something wrong with the lens. your logic is somewhat backwards.

07-25-2012, 01:32 PM   #24
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QuoteOriginally posted by brofkand Quote
I'm going to do some more non-portrait testing of the 50mm.
Here is a post of a test I did testing my m50/1.7 and m50/1.4
QuoteOriginally posted by Schmidlapper Quote
I have placed on Flickr a fairly well controlled comparison of my various normal lens choices, to include A50/1.7, M50/1.4, M50/1.7, SMC Tak 55/1.8, Tamron 17-50/2.8 and a DA55-300/4. The samples shared are for wide open, f5.6 and f8 for center resolution. Corner resolution did not change order of sharpness nor appear out of line. This was only a one lens sampling, but may be interesting, and it helped me change my own usage decisions. I now use my M50/1.7 over my M50/1.4 as my take along bag normal as it was the sharpest of the lot, for pTTL flash portraits I use the A50/1.7 as it was a close second . I had thought my 55/1.8 was not focusing correctly prior to this test based on some photos, but it came in third overall in my opinion in this test. To round out the manuals the M50/1.4 came in fourth for wide open resolution in my view. The link is Collection: My Pentax 50mm normal resolution comparison test and gives the general parameters of my method of testing. I am not picking on anyone else's pet lens but I feel this would be a worthwhile method for anyone who has multiples and variations to determine which is their sharpest. Let me know if this is helpful information on here?
07-25-2012, 10:05 PM   #25
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QuoteOriginally posted by séamuis Quote
if its not sharp at f8, theres something wrong with the lens. if its not sharp by f2 theres something wrong with the lens. your logic is somewhat backwards.
You think so? Then let me explain:

The OP takes a shot with the 50/1.7 at f8, and takes another shot with a 100/2.8. The 100/2.8 seems to be sharper than the 50/1.7. He/she wants to know if this is normal.

We can see the 100/2.8 image appears sharper, but is this because it's a significantly sharper lens (which seems unlikely) or because the 50/1.7 is performing below par? In the absence of definitive information regarding the relative sharpness of the two lenses, we need a test which can prove that the 50/1.7 is indeed below par.

A 50/1.7 is a decent lens, and will be diffraction-limited beyond about f8. So, a good 50/1.7 will show a reduction in sharpness at f16. Only a faulty 50/1.7 will show an improvement at f16. Many types of lens fault will result in better performance at f16, so we now have a pretty definitive test, which is what the OP's after.

I do seem to be spending an awful lot of time on this forum having to explain things which seem obvious.
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