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11-11-2009, 09:58 AM   #1
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what is a good or bad copy of Da*16-50?

In DA* 16-50mm Serial Number Database, people marks good or bad copy of it.
But how do you judge that?

Plus, I will buy a used Da16-50, the seller told me it shows a few mm of back focus at 16mm. Is it common or that means a bad copy?

Thanks~

11-11-2009, 10:25 AM   #2
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I always thought the even numbers were the bad ones
11-11-2009, 10:27 AM   #3
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If you have a K20D you can correct some back or front focus in the Custom Setting menu #35. With my K10D I sent the lens and camera body to Pentax to have them adjust it. The more important issue is how the SDM works.

Last edited by wtlwdwgn; 11-11-2009 at 10:42 AM.
11-11-2009, 10:44 AM   #4
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A bad copy would be mine that is in the shop for aperature blades stuck wide open and a $230 price tag to fix.

11-11-2009, 11:29 AM   #5
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QuoteOriginally posted by nuaabill Quote
In DA* 16-50mm Serial Number Database, people marks good or bad copy of it.
But how do you judge that?

Plus, I will buy a used Da16-50, the seller told me it shows a few mm of back focus at 16mm. Is it common or that means a bad copy?

Thanks~
A percentage of the lenses (not just 16-50) produced by a manufacturer (not only Pentax) can be faulty. The major fault of the 16-50 that causes the lens to be bad is decentered elements. This results in an uneven sharpness at the image's edges. The top left corner might be crisp, the top right corner soft, for example.

To test this, a perfectly flat detailed surface (newspaper taped to plywood, or Lowell's favourite brick wall) is used as a target. The camera is mounted on a tripod with the camera back exactly parallel to the subject. The 2 sec mirror lockup timer is used to expose (avoiding camera shake) and the resulting image examined carefully on your computer to compare all the corners to see that they are the same contrast and focus. The edges will not be as sharp as the centre of the image, very much so at 16mm and f/2.8.

The back focus/front focus issue has to do with the way the lens and the camera body interface when AF is used to focus the picture. The camera thinks the lens is perfectly focused, but the actual point of focus is a few mm in front of or behind where the camera focuses. The k20 and k7 have a system to adjust the focus for each or your lenses so that the AF is spot on. My k10 does not, but can be shipped with the lens to Mr. Pentax for adjustment. If the focus is grossly erroneous, it has been fixed under warranty.

Last edited by Canada_Rockies; 11-11-2009 at 11:35 AM.
11-11-2009, 12:08 PM   #6
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Get the Tamron 17-50mm 2.8
11-11-2009, 12:52 PM   #7
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QuoteOriginally posted by Fl_Gulfer Quote
Get the Tamron 17-50mm 2.8
But if you really want a 16-50 (and for the unrivalled IQ, weather sealing and build quality, I believe it's worth it), just bypass the Tamron 17-50. Although it's a fine lens, it doesn't have the solid feel a quality lens should.

See here also:
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/75030-da-16-50...t-quality.html
11-11-2009, 03:53 PM   #8
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Thanks guys!!!
These help me a lot~

11-12-2009, 01:35 AM   #9
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QuoteOriginally posted by nuaabill Quote
Thanks guys!!!
These help me a lot~
Its a great zoom... my most used lens, stellar quality right throught its range

Neil
11-12-2009, 05:49 AM   #10
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I think that it is pretty easy to tell if you have a good copy. The important thing is not to let user error creep in. If you take a photo of a brick wall, it should be on a tripod, otherwise you'll have a tendency to have one edge of the wall be a little closer and it could make it look softer on that side. The problems that I have seen with this lens from an optical stand point have been pretty obvious, although of course, some are harder to satisfy than others.
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11-12-2009, 07:28 AM   #11
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about good\bad copy:

take a photo to a brickwall (at f2.8 and f5.6) and see if there is the same sharpess in right side and in left side.

if a side is sharper than another side, your lens is not good.
11-12-2009, 09:56 AM   #12
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QuoteOriginally posted by nulla Quote
Its a great zoom... my most used lens, stellar quality right throught its range

Neil
It is my "go to" lens. k10 + 16-50 + 540 at ISO 100 and I get great images even with cropping. Now if I can just get PPG to agree that I take great pictures ...
11-12-2009, 01:54 PM   #13
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After a lot of hesitation I went for a used copy of the 16-50 locally, which was just a month old lens and a replacement for an earlier bad copy (the original owner gave me the paperwork).

The lens produces stunningly sharp photos, even wide-open. However the SDM hesitates once in a while on my K20D even with the updated firmware. But if I take the lens off, clean the contacts, blink three times and tap my right foot once, the lens works like a charm on every odd numbered day if the outside temperature is divisible by 4.

Some times a little prayer seems to help also.
11-12-2009, 02:02 PM   #14
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QuoteOriginally posted by EsBee Quote
After a lot of hesitation I went for a used copy of the 16-50 locally, which was just a month old lens and a replacement for an earlier bad copy (the original owner gave me the paperwork).

The lens produces stunningly sharp photos, even wide-open. However the SDM hesitates once in a while on my K20D even with the updated firmware. But if I take the lens off, clean the contacts, blink three times and tap my right foot once, the lens works like a charm on every odd numbered day if the outside temperature is divisible by 4.

Some times a little prayer seems to help also.
Welcome to the wonderful world of AF with wide angle lenses. You forgot to pull your left ear lobe twice, though. Improves results enormously.
11-12-2009, 02:16 PM   #15
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Comical Albert.
Truthfully, AF on the 16-50 is not always easily locked.
I particularly find AF not locking well at all in moderately low light for subjects at infinity, whereas for the same lighting conditions, close focusing is fine.
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