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09-07-2010, 01:15 PM   #1
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new tamron 17-50mm f/2.8 question

Hi All,

long story short, first copy had severe front focus problem, had to use debug mode and go -80 micro meter in AF adjustment. replacement lens arrived and here are two new issues i face:

1. with no AF adjustment from debug mode (0 micro meter) i noticed a pretty bad case of back focus at f/4.0 and f/4.5, got better at f/3.5 and f/5.0 (though center area is still out of focus), other aperture setting are acceptable though not perfectly centered. this is happening through out the zoom range, i spot tested at 17mm, 24mm, 35mm and 50mm.

2. image soft at f/2.8 when pixel peeping, compared to other aperture settings

I will post some pix when i get home tonight

but my question is, should I give Tamron and this lens another try and go through another RMA process? or is there another comparable lens in the $400 new price range I can get?

09-07-2010, 01:51 PM   #2
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I got the Pentax 16-45mm after going through 3 copies of the Tamron with front focus. The 16-45mm is excellent, and as I later realized, the 16mm (with minimal distortion) is much more useful than 2.8 constant aperture. First, a couple of fast primes will be better than the zoom at 2.8; second, I personally need some DOF between 16mm and, say, 24mm.

This is not to say the Tammy 17-50mm isn't an excellent lens--provided you come across a good copy. (It might make sense to look for a used one.)
09-07-2010, 05:52 PM   #3
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can you post how you determine if your lens has focusing issue. I have noticed my photos either being soft or having to press the shutter half way several times to focus correctly. I just assumed its something im doing but i dont seem to have this problem with my da15 or dal 55-300.

thanks in advance and sorry for the hijack but im curious.
jorge
09-08-2010, 10:47 AM   #4
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I did a AF chart test: Nikon D70 Focus Chart basically I downloaded and printed the chart from that link, and then i did the following: 1. mount camera on tripod, 45 degree downward towards chart, 2 ft away 2. iso 200, 2-sec timer 3. then i just go through aperture (2.8, 3.5, 4.0, 4.5, 5.6, 7.1) 4. at each aperture, i followed focal range marking on the lens (17mm, 24, 35, 50) 5. finally, i pixel peeped at each picture and came to my original post's conclusion
QuoteOriginally posted by boosted03gti Quote
can you post how you determine if your lens has focusing issue. I have noticed my photos either being soft or having to press the shutter half way several times to focus correctly. I just assumed its something im doing but i dont seem to have this problem with my da15 or dal 55-300.

thanks in advance and sorry for the hijack but im curious.
jorge


09-08-2010, 05:33 PM   #5
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But how did you determine that any issue yu had was with the lens and not the camera? it seems people often leap to the conclusion that the lens is responsible for any discrepancy they see, but all logic suggests the camera would be at fault more often. And that it wouldn't be noticeable on slower lenses, which is probably part of how people get the mistaken impression that the lens is at fault. I'm not saying I know it's *not* the lens, but I'm suspicious. Wouldn't hurt to see some of the test shots.

Also, hardly any lens is optimally sharp wide open. so no surprise it's softer at f/2.8 than other apertures.
09-08-2010, 06:05 PM   #6
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If all you did was to test it at home, take it outside to produce some real life shots. If the results you get are still unsatisfactory, then you can conclude it's not a good copy (or not the right lens for you). Sharpness tests are very often misleading, since their success depends on too many variables. BTW, did you test the lens in bright natural light? AF can be fooled by artificial light.
09-08-2010, 10:10 PM   #7
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I can't speak for the front/back focusing issue, since I rarely notice it on my copy (and I couldn't do anything about it anyways as I have a DS). As for the softness at f2.8, I find mine to be a little soft at the wide end at 2.8 but better at 4.0 and 5.6, and still perfectly usable at all apertures. It's not as sharp as my FA35/2, but I don't expect it to be.
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