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01-25-2008, 12:30 PM   #1
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Quick question on the 16-50mm picture quality

I'm just beginning on my photography journey, but I was able to snag a 16-50 with my christmas funds. So I have the lens finally, but after reading about everyone's problems with the lens I decided to test mine out, and by test I mean shoot pictures and ask other people's opinion.

I feel like something looks wrong, but I'm not sure.


my kitchen


100% crop


I focused on the bag of pretzels.

01-25-2008, 12:34 PM   #2
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IMHO a definite focussing problem. I feel one can only approach purchasing this lens with great uncertainty. Shame it has to be like that. I'd get it checked out/ or exchanged if I were you.
01-25-2008, 12:44 PM   #3
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Ah ... I was hoping I had just done something wrong. Oh well ... Maybe Pentax will give me a 20d for my problems
01-25-2008, 01:18 PM   #4
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The camera angle appears high, about at eye level, so I might speculate that it was hand-held, not tripod-mounted.

The picture appears naturally lit, not flash-lit.

How, therefore, have you excluded camera shake as a potential source of lack of sharpness?

Also, if the pretzel bag was what you focused on, you must have reframed, since it is not in the centre of the shot. Either that, or the camera may have chosen an AF point other than the centre to focus on.

So how are you sure that the camera-to-subject distance hasn't changed between focusing and shooting, or that the camera isn't in fact focused other than at the centre of the frame?

What exposure and aperture did you use?


Last edited by ChrisA; 01-25-2008 at 01:25 PM.
01-25-2008, 01:47 PM   #5
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Those pictures are definitely out of focus. Did you manually focus or auto focus?
01-25-2008, 01:51 PM   #6
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Its hard to tell without being able to zoom in everywhere, but if nothing is in focus I would say its probably camera shake too. If the focus of the lens is simply off, either from focusing and reframing, or a poor job of manual focus, or even the lens is wrong, then there would be some place in the shot that is in focus. I am also curious as to what the f-stop and ss is, that could help out here as well. Try it again on a tripod, or make sure your ss is fast enough to eliminate the possibility of camera shake.
01-25-2008, 04:16 PM   #7
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It is impossible, for me anyway, to determine on the basis of that one photo if you have a problem with your lens. If you go to Photozone, you can find a good article on how to test your lens for a problem. I will reproduce it here for your convenience.


"Q: How can I find out whether my lens has a problems ?

Describing the procedure is easy. The execution is very difficult ...

1. Plug a couple of news paper pages to a wall with a coverage of about 120x80cm.
2. Place a print with a black square in the center (say 10x10cm).
3. Mark all four corners with a red point and connect the points with a line - this should result in a PERFECT rectangle.
4. The camera-to-wall distance should be sufficient to cover the newspaper in the viewfinder but not bigger. The four red points MUST BE VISIBLE in the extreme-most corners of the viewfinder or better in the TFT after taking a shot. The rectangle must not be tilted! Check this with a couple of sample shots at f/11. Forget water-level devices - these are not accurate enough because they don´t measure the optical path.
5. Then do _numerous_ fine-stepped manual focus iterations around the suggested focus distance supplied by the AF - at least 20 iterations between the two points where the image gets out-of-focus on either side. You need to do that at wide-open aperture and maybe 1 stop down. In the analysis you should be able to find one image where the center is perfectly in-focus and another one where all four corners are in focus (due to the quite common field curvature you will usually not find a perfectly sharp center and corner on the same image). In case of a zoom it should be sufficient to run this test at the most extreme focal lengths.

There´re a couple of indications whether your lens has a centering problem:

1. the black square. If one or more lens groups are "loose" they tend to follow gravity. This is visible via the black square. The horizontal edges will be blurred or show a halo effect whereas the vertical edges are sharp(er). This is a frequent problem with VR/IS lenses or zooms that extend significantly.
2. one of the corners or a whole side is blurred whereas the other corners are not. Usually you will be able to find an in-focus frame for the "problem" spot in another focus iteration or none at all. If the corner remains blurred across all focus iterations you should send the lens straight to the service department. If the "problem" spot is sharp on a neighboring focus iteration this is still Ok and not field relevant. Counter-check with the stopped down image in this vicinity. If you find the sharp focus in a "distant" iteration consider servicing.

Please be aware that this analysis REQUIRES an absolutely perpendicular setup and this is the problem. If the setup is sub-optimal you run into simply out-of-focus scenarios that are no indication for a problem whatsoever. This is specifically a problem with fast lenses (f/2.8 and faster) where the DOF is extremely shallow wide-open. Please note that it is absolutely unrealistic to have a perfectly centered lens - it just does not exist. In case of a slight centering problem you should not send it to the service department simply because there´re limits of what they can do. They may even make it worse after all (not unheard of) or simply return it arguing that the lens is within factory limits. If I was a normal user I would run this procedure only if there´s reason to be suspicious. Otherwise you just risk loosing your sanity."

As an aside, you might be interested to know that the DA* 16-50mm lens that
Photozone tested had centering defects that were so severe, they pulled the review in the interests of fairness to Pentax.

In any case, I hope after all testing is said and done that you have a lens you are happy with.
01-25-2008, 08:16 PM   #8
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QuoteOriginally posted by Tbear Quote
It is impossible, for me anyway, to determine on the basis of that one photo if you have a problem with your lens. If you go to Photozone, you can find a good article on how to test your lens for a problem. I will reproduce it here for your convenience.


"Q: How can I find out whether my lens has a problems ?

Describing the procedure is easy. The execution is very difficult ...

1. Plug a couple of news paper pages to a wall with a coverage of about 120x80cm.
2. Place a print with a black square in the center (say 10x10cm).
3. Mark all four corners with a red point and connect the points with a line - this should result in a PERFECT rectangle.
4. The camera-to-wall distance should be sufficient to cover the newspaper in the viewfinder but not bigger. The four red points MUST BE VISIBLE in the extreme-most corners of the viewfinder or better in the TFT after taking a shot. The rectangle must not be tilted! Check this with a couple of sample shots at f/11. Forget water-level devices - these are not accurate enough because they don´t measure the optical path.
5. Then do _numerous_ fine-stepped manual focus iterations around the suggested focus distance supplied by the AF - at least 20 iterations between the two points where the image gets out-of-focus on either side. You need to do that at wide-open aperture and maybe 1 stop down. In the analysis you should be able to find one image where the center is perfectly in-focus and another one where all four corners are in focus (due to the quite common field curvature you will usually not find a perfectly sharp center and corner on the same image). In case of a zoom it should be sufficient to run this test at the most extreme focal lengths.

There´re a couple of indications whether your lens has a centering problem:

1. the black square. If one or more lens groups are "loose" they tend to follow gravity. This is visible via the black square. The horizontal edges will be blurred or show a halo effect whereas the vertical edges are sharp(er). This is a frequent problem with VR/IS lenses or zooms that extend significantly.
2. one of the corners or a whole side is blurred whereas the other corners are not. Usually you will be able to find an in-focus frame for the "problem" spot in another focus iteration or none at all. If the corner remains blurred across all focus iterations you should send the lens straight to the service department. If the "problem" spot is sharp on a neighboring focus iteration this is still Ok and not field relevant. Counter-check with the stopped down image in this vicinity. If you find the sharp focus in a "distant" iteration consider servicing.

Please be aware that this analysis REQUIRES an absolutely perpendicular setup and this is the problem. If the setup is sub-optimal you run into simply out-of-focus scenarios that are no indication for a problem whatsoever. This is specifically a problem with fast lenses (f/2.8 and faster) where the DOF is extremely shallow wide-open. Please note that it is absolutely unrealistic to have a perfectly centered lens - it just does not exist. In case of a slight centering problem you should not send it to the service department simply because there´re limits of what they can do. They may even make it worse after all (not unheard of) or simply return it arguing that the lens is within factory limits. If I was a normal user I would run this procedure only if there´s reason to be suspicious. Otherwise you just risk loosing your sanity."

As an aside, you might be interested to know that the DA* 16-50mm lens that
Photozone tested had centering defects that were so severe, they pulled the review in the interests of fairness to Pentax.

In any case, I hope after all testing is said and done that you have a lens you are happy with.
Thanks, I looked for instructions on how to test it properly and I didn't really come up with anything. When I first got the lens I toyed around with a tripod and taking pictures of really small print. At f2.8 I was not able to read the text, but as I stopped down the lens it became slightly clearer. So I wasn't sure what the problem was. Anyway I'll try this out tomorrow. Thanks again.

01-26-2008, 07:40 AM   #9
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QuoteOriginally posted by superbass Quote
Thanks, I looked for instructions on how to test it properly and I didn't really come up with anything. When I first got the lens I toyed around with a tripod and taking pictures of really small print. At f2.8 I was not able to read the text, but as I stopped down the lens it became slightly clearer. So I wasn't sure what the problem was. Anyway I'll try this out tomorrow. Thanks again.
No problem. Let us know the results of your testing.
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