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12-14-2008, 12:32 PM   #16
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thanks guys for the comments

how do I properly confirm if the tamron has a front focus issue ? Also if it does, is this grounds for replacement/fix under warranty ? Never had to RMA any DSLR gear so no idea heh.

Also curious, for front focus impaired lens when they go back for RMA are they fixed/repaired or replaced ? How are the fixed ?

Thanks

George


Last edited by eva2000; 12-14-2008 at 12:52 PM.
12-14-2008, 01:01 PM   #17
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QuoteOriginally posted by eva2000 Quote
how do I properly confirm if the tamron has a front focus issue ?
Here you go.
12-14-2008, 04:39 PM   #18
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very good work, hahah probably asking much to see corner crops too
always unsure whether the Sigma or Tamron is better. the tamron always gets good reviews everywhere whereas the Sigma doesn't seem as popular. but then popphoto fwiw said the sigma is better so always not sure.
12-14-2008, 09:40 PM   #19
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Here is my Tamron 17-50mm on a K10D:
Taken at 50mm, F4, 1/10s, spot metering, aperture mode, 100% crop



12-15-2008, 08:34 AM   #20
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QuoteOriginally posted by Miserere Quote
Here you go.
Anyway did some Tamron focus tests and seems i maybe front focusing https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/44118-tamron-1...-focusing.html

Last edited by eva2000; 12-15-2008 at 10:23 AM.
12-17-2008, 07:25 AM   #21
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QuoteOriginally posted by Torphoto Quote
Not only could the tammy be front focusing, also bear in mind sample variation, not so good tammy vs very good sigma sample. The F8 tests show that it is possible the tammy is probably a not so good sample, FF or not.
I really wouldn't call that Tammy "not so good" even with those results. These details are at a level that are difficult to achieve in the real world.

I have been buying and trying to evaluate lenses (mostly for Pentax) for 40 years, and I find it very difficult to arrange a test setup that works consistently at this level. The tripod must be set in stone, the mirror up, and, if outdoors, the air must be perfectly still. Focus must be spot on for each lens, and the lens perfectly parallel to the wall each time. Since I moved to AF digital SLRs, it is even more frustrating because of AF quirks.

I gave up my quest for test after purchasing a Sigma 17-35mm EG 2.8, and spending two days with a tripod trying to compare it to primes shooting a wall with a K10d. The Sigma kept coming up short on the edges, with a difference comparable to what I see in these photos. Fine, I thought. This is a zoom and you expect that. Then, I picked up the camera and took a few last hand-held grab shots, and the sharpness was stunning--much closer to the primes. What turned out to be a tiny bit of backfocus hadn't happened on this occasion. My change in technique or a change in light had somehow caused the AF to lock properly.

I think we sometimes do obsess a bit about sharpness issues that are eclipsed in the real world by a myriad of variables. I am now more inclined to shoot a lot of oft-photographed subjects near me with the lens, in a lot of situations, and see how I feel about the results.
12-18-2008, 02:09 AM   #22
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QuoteOriginally posted by eva2000 Quote
Thanks guys.. the original tests with resized photos had sigma and tamron pretty close... was surprised by the cropped results though.
Of course I'll do other tests/photo subjects later to compare.
That's what I always write in this forum: only 1:1 crops can say a thing about lens. Everything else is about the photographer.
This work prooves my point.
Thanks
12-18-2008, 02:17 AM   #23
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QuoteOriginally posted by GeneV Quote
I think we sometimes do obsess a bit about sharpness issues that are eclipsed in the real world by a myriad of variables. I am now more inclined to shoot a lot of oft-photographed subjects near me with the lens, in a lot of situations, and see how I feel about the results.
At the end that is the proper way: all we do is for usfeeling good. So the feeling good factor is of outmost importance ...
... but for facts accepted by everyone, proper testing (in a scientific way) is due...

12-18-2008, 06:31 AM   #24
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QuoteOriginally posted by gkopeliadis Quote
... but for facts accepted by everyone, proper testing (in a scientific way) is due...
I agree. However, I think that despite our best efforts, very few of us can really do that in a way that both controls the variables and is meaningful to real photography.
12-21-2008, 03:40 AM   #25
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QuoteOriginally posted by gkopeliadis Quote
That's what I always write in this forum: only 1:1 crops can say a thing about lens. Everything else is about the photographer.
This work prooves my point.
Thanks
Tomorrow i have advance replacement copy of Tamron 17-50mm 2.8 coming so will be able to compare both Tamron 17-50mm and Sigma again
12-21-2008, 03:57 AM   #26
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that tamron looks pretty much how my 50-135 looked before doing some AF adjustments for FF. you couldve either manually focused the tamron (perhaps using 8x on liveview) or taken a series of shots adjusting AF by 2 in either direction (+ or -), looked at the results and then fine tuned from there.
12-21-2008, 04:16 AM   #27
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K200D doesn't have AF adjustments
12-21-2008, 08:43 AM   #28
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darn diddly
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