[basikal_kusayang]

Hi, i got a Tamron 17-50 f2.8 for my K200D. When I shoot with this lens, most of the time, I will end up focusing something behind the subject. Is this what you call back focusing problem?or it is normal for lenses like this one?

[JeffJS]

Sounds like back focus to me. Do your other lenses do it (because it can happen with Any lens)?

[agsy]

I had focus problems with one of my lenses and I found this site very helpful. Tamron lenses are known for ff/bf issues.

[mikem]

My first copy of that lens had atrocious front focus. Fortunately the retailer was happy to swap it out for another copy that was spot on for my body.

[rawr]

My first copy of the 17-50 also had horrendous problems with focus and image quality due to de-centering, possibly caused by a knock or two during shipping. If pain persists, send it in under warranty if that is an option.

Another thing to keep in mind is that when shooting wide with the Tamron there is considerable field curvature of the focal plane.

This means that "...the focus plane isn't flat but it bends towards to corners. As a consequence you will end with out-of-focus corners when shooting flat or very deep objects at large aperture settings ...The problem will be reduced when stopping down thus increasing the depth-of-field around the curved focus plane. "
(Quote from the photozone review of the Tamron 17-50 in Canon mount)

[Laurentiu Cristofor]

Hi, i got a Tamron 17-50 f2.8 for my K200D. When I shoot with this lens, most of the time, I will end up focusing something behind the subject. Is this what you call back focusing problem?or it is normal for lenses like this one?

Make sure the focus points that light up in the viewfinder are on top of what you want in focus. Select the AF point if you need more control where the camera autofocuses.

And do post some sample images if you want to get the best advice.

[mlatour]

I've been using the Sigma equivalent: a 18-50mm f2.8 EX DC MACRO for over a year
and always looking for sharper results @ f2.8 had tested a copy of the Tamron last winter,
not impressed with the bf/ff issues I returned it a few days later.

Since then discovered the now 'not-so-secret' K-x DEBUG_MODE trick and a couple of weeks ago
decided to give Tamron a 2nd chance while I sent my Sigma in for some warranty work.

I tested three copies of the Tamron 17-50mm f2.8 on the camera shop's counter
using a focus test chart until I found the one that worked the best with my K-x,
back home I still had to fine tune a bit of back-focus problems with the "DEBUG_MODE trick" to get it to focus perfectly.

I now like it so much that once my Sigma is back from repair its most likely
that it will become the spare lens and the Tamron will continu as my main lens.

If you find a 'good' copy, the Tamron is certainly a nice/sharp f2.8 zoom lens at
a decent price, but I would only recommend it to anyone wanting to buy that :

1) you can test/exchange it until you find a 'good' one that matches your camera
2) have AF micro-adjustments available in your camera's functions
3) are willing to play in the DEBUG_MODE to fine tune if your camera doesn't have above#2

Michel

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Last edited by mlatour; 07-25-2011 at 02:50 AM.

[basikal_kusayang]

Thanks a lot for the help guys. I'll try to return it to the seller. But, how am I going to tell the seller that I have this problem?I bought it online. Do i have to send a sample photo? (Im just wondering because this is the firtst time I had this problem)..

[basikal_kusayang]

Sounds like back focus to me. Do your other lenses do it (because it can happen with Any lens)?

No, i dont have any problem with my other lens.

[basikal_kusayang]

Make sure the focus points that light up in the viewfinder are on top of what you want in focus. Select the AF point if you need more control where the camera autofocuses. And do post some sample images if you want to get the best advice.

I tried to focus manually. it works but sometimes my sbject is still OOF even when the focus point light up.

[Laurentiu Cristofor]

I tried to focus manually. it works but sometimes my sbject is still OOF even when the focus point light up.

I wasn't recommending focusing manually, but you could select the AF point, place it over the area you want to focus on, and then let the camera focus on that area using that AF point. If you let the camera pick the AF point, it may focus on other objects than those you meant to focus on.

[civiletti]

My first copy of the 17-50 also had horrendous problems with focus and image quality due to de-centering, possibly caused by a knock or two during shipping. If pain persists, send it in under warranty if that is an option.

Another thing to keep in mind is that when shooting wide with the Tamron there is considerable field curvature of the focal plane.

This means that "...the focus plane isn't flat but it bends towards to corners. As a consequence you will end with out-of-focus corners when shooting flat or very deep objects at large aperture settings ...The problem will be reduced when stopping down thus increasing the depth-of-field around the curved focus plane. "
(Quote from the photozone review of the Tamron 17-50 in Canon mount)

Field curvature is a problem at 17mm and less so at longer focal length.