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06-21-2011, 01:58 AM   #1
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Tamron bad QC or Pentax compatibility issue?

Hi guys. I've been trying for a while now to buy a walkaround lens for my Pentax K5. Because of the good optical quality and great price I decided to go for the Tamron 17-50 f2.8.

When I received the lens I noticed straight away some FF problems at the long end. No problem, I said, the K5's AF fine tune will fix it. And after a -10 correction it did. Only to realize now that my wide end was BF-ing like hell. So when I fix the focus at the long end I mess up with the wide end and the other way around. I tried every single step from -10 to +10, I used special charts, indoor light, outdoor light, always the same problem. There was no way of having both ends focus properly. It wasn't a simple FF or BF problem that can be easily corrected by the camera. I also checked the lens on my old K10 with the same results.

I sent the lens back and got a replacement. It had EXACTLY the same problem. At first I thought the seller sent me back the same lens but I checked the serial numbers and they were different. However the serial numbers were only 4 digits apart so I concluded that maybe the whole batch was faulty. I sent this one back as well and got a refund and decided to try the Tamron 28-75 instead because I found the 50mm zoom not being long enough. I got one from a different seller and.....surprise.....exactly the same problem........WHAT IS GOING ON?!

So I tried 3 lenses on both my bodies, K5 and K10, and all had the exact same problem. I even enabled K10's debug menu so I can adjust the focus but i got the same results as the K5. It was impossible to achieve good focus at both ends at the same time. Also good focus in the macro range was bad focus in the distant +5m range and the other way around.

Because all 3 lenses behaved identically I must say i become a little bit paranoid.....Is Tamron's QC this bad? Have I been unlucky? Are the cameras bad? Is Pentax not compatible with these lenses? All my other 4 lenses work very well on both bodies but none of them have such small f numbers(f4 is the lowest).

I need some help please! Any thoughts? Anybody else having the same problems? Thank you.

Last edited by Nicks; 06-21-2011 at 02:03 AM.
06-21-2011, 05:21 AM   #2
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Not Tamron. More likely your K5.
06-21-2011, 05:58 AM   #3

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I have both 17-50mm and 28-75mm and both spot on with my two K-x and a K100D. However, I did heard some complaints about Bf/FF issues with Tamron though not as bad as in your case.
06-21-2011, 06:29 AM   #4
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My 17-50 focus is spot on with my K-5 and K-20D, however, wide open it is soft on the left side...

06-21-2011, 06:44 AM   #5
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My Tamron 17-50 is also spot on both with my K5 And K7.
06-21-2011, 06:49 AM   #6
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Nicks, google "Tamron 17-50" and "front focus" and look at the hundreds (or thousands) of hits and not just in Pentax mount... Tamron's QC on that lens is spotty at best.

I also have a 17-50 thats front focuses so much that it's unusable below f4 (tested on K100, K20 and K5).


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