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09-30-2010, 10:25 AM   #1
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Is my 16-50mm DA* a dud?

Hi,

I'm fairly green at digital photography especially with a DSLR. My Pentax K10D is the first I've owned. I bought the best lens I could for it in 2007--the 16-50 DA*. Lately, I've reviewed a poor shot here and there on the computer and haven't been able to blame myself for it. So I started researching issues with this lens, primarily reading this forum, which brought my attention to the image quality issues this lens has had. Its an early copy of the lens, serial number 9010776.

I've taken a number of test shots of a brick wall at multiple focal lengths and apertures. Some of the results were painful viewing. The images look quite obviously poor at the extremes (wide angle, f/2.8) and I suspect that my lens is a bad copy but I really need an expectation reset from more experienced photographers respecting image quality. How soft is acceptably soft at the extremes? Is my lens a not-so-hot copy or a REALLY bad copy. Could I prevail upon someone for their opinion?

Attached images are 16mm @ f/2.8, 3.5, 5.6 and 50mm @ f/2.8, 5.6

Much obliged!

Jason

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09-30-2010, 11:58 AM   #2
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I don't own that lens so I have no direct comparison. However, compared to other shots from that lens I've seen, it does not seem super crisp.

Obvious barrel distortion, but that could be normal.

Note that all lenses appear soft in the corners when wide open and close to the subject. That is because you focus on the center which is relatively closer to the camera, so the corners are simply and normally out of focus a bit.

I'm assuming you have gotten better real-world shots.
09-30-2010, 12:06 PM   #3
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It's a simple equation:


Dud - SDM + Vietnam Quality Standards
09-30-2010, 12:52 PM   #4
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based on these pictures, your lens is ok.

09-30-2010, 01:06 PM   #5
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QuoteOriginally posted by donallison13 Quote
It's a simple equation:


Dud - SDM + Vietnam Quality Standards
That's simply nonsense.
The quality has nothing to do with what country the lens is assembled in.
As for SDM, that's another issue altogether.

On IQ, there are a plethora of similar threads all basically saying the same thing. "My copy is bad as is shown in this brick wall test". Most of them had no idea how to conduct a test that exemplifies the IQ of the lens, and here you've shown us much of the same. You must have been so close to the brick wall that not only is the barrel distortion so obvious but also there would be no possible way that "flat" surface you're capturing remains flat over the lens plane. Hard to grasp? See here:

Focus and Recompose

Then reconsider either your technique or forget about trying to test the lens altogether and just go out there and shoot real-life f/2.8 shots and see how you go.

The DA* does perform very well when focus is nailed and IQ is unrivalled, despite my comparison with the 16-45 here:

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/49602-da%2A-16...e-quality.html
09-30-2010, 04:09 PM   #6
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The bottom edge looks really bad, but it's hard to tell if that's due to incorrect alignment with the wall or an actual defect.
09-30-2010, 04:40 PM   #7
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Ash
the images from your lens comparison have been moved or deleted by photobucket..any chance of fixing that...?
09-30-2010, 04:46 PM   #8
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QuoteOriginally posted by deadwolfbones Quote
The bottom edge looks really bad, but it's hard to tell if that's due to incorrect alignment with the wall or an actual defect.
I'm betting it's alignment with the wall. There isn't a lot of room for error at f2.8 on the 16-50, especially close up. Early copies of this lens had decentering defects and the problem, if I remember correctly would show up in left to right alignment, not top to bottom.

If you Really want to check this lens, use a newspaper or similar, in a well lit area, no flash, make srue it's properly aimed and focused at f2.8 16mm. If you have a problem copy (which I don't think you do), you will see halo'ing around one side of the print type, making it look like it's out of focus.



09-30-2010, 08:32 PM   #9
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Thanks all for the feedback! Yeah, I was maybe half a meter from that brick wall. The Focus and Recompose article, Ash, was very enlightening--forgot my trig! Makes sense. I'll try some very deliberate real world f2.8 shots and the newspaper technique (maybe a little farther away!)
09-30-2010, 10:50 PM   #10
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QuoteOriginally posted by Tommot1965 Quote
Ash
the images from your lens comparison have been moved or deleted by photobucket..any chance of fixing that...?
Mate, I wouldn't bother about those - even my images weren't good examples of the lens's IQ. Going through the discussion of that thread you'll see why...
10-01-2010, 02:10 AM   #11
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no worries mate,,
10-01-2010, 02:59 AM   #12
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The problem with this test or any newspaper test with such lens is that the results would never be conclusive because this is not a flat field lens, and it gets much worse at closeup distance. If you want something more meaningful, put your camera on tripod, and shoot some real scenery with 2s timer. This lens is known to be quite soft wide open at 16mm. However, softness could be caused by BF/FF too. The sign of misalignment is uneven sharpness from right to left, or top to bottom, or nothing is sharp except the centre. Also, for such small jpegs, it is impossible to tell anything except your f2.8 shots are very soft.
10-01-2010, 04:34 AM   #13
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I agree with the others. The 16-50 is really soft around the edges at 16mm and f2.8. It should sharpen up by f4/18mm. If that is the only place that you see some softness, then I wouldn't worry about it. The issues in the beginning with this lens were decentering and would give softness on one half of a photo as compared to the other half. It does tend to get a little soft at 50mm and wide open, but not nearly as bad.
10-01-2010, 08:44 AM   #14
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No issues based on these images. There is a lot of barrel distortion with the D*16-50/2.8 at 16mm. It is also a little soft at f 2.8 especially at the edges. I was aware of the distortion issue before I purchase but was still a bit surprised at the degree of distortion.

This lens performs extremely well stopped down a bit and under normal shooting conditions is capable of amazing results.

Tom G
10-01-2010, 01:04 PM   #15
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QuoteOriginally posted by Rondec Quote
The 16-50 is really soft around the edges at 16mm and f2.8. It does tend to get a little soft at 50mm and wide open, but not nearly as bad.
QuoteOriginally posted by 8540tomg Quote
No issues based on these images. There is a lot of barrel distortion with the D*16-50/2.8 at 16mm. It is also a little soft at f 2.8 especially at the edges.
We can't accurately 'test' edge softness at 16mm and f/2.8 - there is no subject matter 'curved' accurately enough for the lens to have equidistance from the subject plane to the lens and sensor for this to be ascertained.

So the image softness wide open is more likely due to Gaussian (or OOF) blur more than anything. That's why these kind of tests are thwart with limitations, and when we start making judgements on the lens based on our inaccurate interpretations of the data, we begin to question the overall IQ of the lens when there really wasn't an issue with the lens in the first place.

Just shoot, don't test!

Last edited by Ash; 10-01-2010 at 01:11 PM.
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