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07-24-2010, 08:56 PM   #1
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After getting 2 bad copies, what next?

Just bought tamron 17--50 2.8 as kit lens upgrade and have gotten 2 bad copies, both of which have severe front focus problem... So guys, please give me some advice, if I should have my finger crossed and exchange for the 3rd copy or just go with the 16--50 SDM? Or other choices that have 2.8 aperture and wide angle?

Now I find it's actually very hard to buy a new lens, 17--50 has bad QC and 16--50 has unstable SDM... I am kinda despair

thanks for any help

07-24-2010, 09:35 PM   #2
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Are you positive there is a problem with the lens as opposed to with your camera or with your testing methodolgy? Have you cross checked the lens on other bodies, or other lenses of the same focal length and aperture on your body? Could you post your focus test chart results?
07-24-2010, 10:19 PM   #3
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QuoteOriginally posted by shang Quote
Just bought tamron 17--50 2.8 as kit lens upgrade and have gotten 2 bad copies, both of which have severe front focus problem... So guys, please give me some advice, if I should have my finger crossed and exchange for the 3rd copy or just go with the 16--50 SDM? Or other choices that have 2.8 aperture and wide angle?

Now I find it's actually very hard to buy a new lens, 17--50 has bad QC and 16--50 has unstable SDM... I am kinda despair

thanks for any help
Are you testing it indoors where tungsten light can cause FF?

I've read a post that suggested just sending it in to the factory for repair. i think it was a Tamron. I've got a Tamron 28-75 that is also FF, but correctable within K20's ability to correct.
07-24-2010, 11:24 PM   #4
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Switching from one ill-designed lens to another? Well, I don't know. Maybe it's time to try some Pentax primes, or buy Canon for their 2.8 zooms. I am certain there are awesome copies on the market, but much depends on your luck and persistence. Good luck, you seem to need it.

07-25-2010, 12:02 AM   #5
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I personally quit testing my lens. It can show focus problems almost every time i test. When i leave it alone and just shoot I seem to be happy with the results. That is what counts.
I try not to think about it and if the lens is producing then i leave it alone. I have had one lens that was front focusing and i screwed with it for ever. It is very frustrating. But even at that. If you send it in they will calibrate it to your camera.

Post some pics and let us see your problem.
07-25-2010, 12:17 AM   #6
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I had the same problem--2 copies of Tamron 17-50mm with front focus--then bought a DA 16-45mm. Couldn't be happier. To be frank, now I would choose the 16-45mm over the Tamron even if I was warranted to have a good copy of the Tamron, simply because I wouldn't use a wide zoom at 2.8 (I have primes for that) and because stopped down the Pentax 16-45mm is excellent at 16mm, whereas the Tamron shows much more dramatic distortions at 17mm. I like the 16-45mm so much, that I was tempted to get a second one--for the case I drop and ruin one copy.
07-25-2010, 04:17 PM   #7
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thanks guys! I didn't try the lens on other bodies since I cannot find anybody using pentax around me... So a lens can perform differently on different bodies, I am now using Km, so if I get a new K-7, may this become a good copy? thanks!
07-25-2010, 09:11 PM   #8
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QuoteOriginally posted by shang Quote
thanks guys! I didn't try the lens on other bodies since I cannot find anybody using pentax around me... So a lens can perform differently on different bodies, I am now using Km, so if I get a new K-7, may this become a good copy? thanks!
You missed Marc's point entirely.

I think he was politely suggesting that there's a good possibility of user error if you've got two bad copies of the same lens.

It's very possible that this is a "good copy" and you're just using it poorly. The only way to know for sure is to use focusing test charts before blaming the lens.

07-26-2010, 04:12 AM   #9
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Well, the problem could be the camera. I don't know of any debug mode for the Km, but the K20 and K7 have the ability to tweak autofocus on various lenses, which comes in handy. If it were a Pentax lens, you could send it, with the camera, to Pentax, but unfortunately with third party lenses, Pentax usually tells you that it is the lens maker's problem.
07-26-2010, 04:21 PM   #10
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Yes, I was suggesting testing error is one possibility. But I was also pointing out that a camera problem is also quite possible - and indeed, probably more likely than having two defective lenses. But until we see test images, I wouldn't rule out out testing error.

Last edited by Marc Sabatella; 07-27-2010 at 02:43 PM.
07-26-2010, 11:48 PM   #11
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QuoteOriginally posted by shang Quote
Just bought tamron 17--50 2.8 as kit lens upgrade and have gotten 2 bad copies, both of which have severe front focus problem... So guys, please give me some advice, if I should have my finger crossed and exchange for the 3rd copy or just go with the 16--50 SDM? Or other choices that have 2.8 aperture and wide angle?

Now I find it's actually very hard to buy a new lens, 17--50 has bad QC and 16--50 has unstable SDM... I am kinda despair

thanks for any help
Given your location, is it possible for you to drive to B&H or Adorama to try out a copy there? I would think it's worth the effort and one of the reasons buying from a nice camera store in your area is a great advantage. Just make sure they have a few copies in stock before visiting the store.

Plus if you are nice, and by NY Camera store standards who knows what that really means... :P but you might be able to try out your FF'ing copy on a K-7 since you are in the market for a K-7 anyway. but again make sure ahead of time so nobody gets their time wasted.

Some are very quick to pull the "user error" trigger and others to blame the hardware...I find it is best to figure out a way to verify the hardware first. There are some Canon "L" which will take half a dozen copies to find one that matches the parameters on whatever Canon body you have be that an xxD series or an 1D III/IV series...it's not uncommon because there are so many factors which come into play. Sure always make sure it's not you but if you know yourself well enough and have played around with your gear enough you can tell right away if it's you or the hardware...I had the same issue with a 35ltd a few months back...I just knew right off the thing was completely wrong on my body...B&H was great and we did a swap with perfect results...night and day difference too.
07-29-2010, 01:34 AM   #12
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thanks guys! yeah, i may go to NYC to try out new copies and DA*16-50 and fortunately my k-7 is on the way. Will post photoes after I make a 3d test chart. I find it very hard for me to set up a test environment using a paper test chart.... thanks a lot!
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