[lux-ad-artem]

I've been using the above-named lens along with my Pentax K20D since April. I purchased it used from Henry's [camera store] in the Greater Toronto Area. I've been relatively satisfied with its performance compared to my kit lens, but recently I've noticed something that qualifies as a bizarre problem/annoying quirk.

While editing photos shot with this lens, Lighroom has identified an unusually large amount that were supposedly shot at a 45mm focal length.
To make a long story short, yesterday I ended up investigating this problem. It turns out that if I have the lens zoomed out as far as it goes, to the point that I can't turn the zoom ring any further, the camera itself indicates its focal length is 45mm. If I rotate the zoom ring just ever so slightly away from the widest point – not even enough to change the frame, it displays the focal length as 17mm, which it should be.
Has anybody else experienced this? Does anybody have any explanations? Presumably, there's no reason to believe that this is an indication of any, more major, underlying problems?

TL; DR - When the zoom ring of my Tamron 17-50 Di-LD II is rotated to its widest point, my Pentax K20D records the focal length as 45mm instead of 17mm. If I rotate the zoom ring just slightly away from its widest point, it records a focal length of 17mm. It's much like I'm simply breaking a circuit or something.

[Laurentiu Cristofor]

TL; DR - When the zoom ring of my Tamron 17-50 Di-LD II is rotated to its widest point, my Pentax K20D records the focal length as 45mm instead of 17mm. If I rotate the zoom ring just slightly away from its widest point, it records a focal length of 17mm. It's much like I'm simply breaking a circuit or something.

It's either a camera issue, lens issue, or camera-lens communication issue.

To eliminate the camera, try another lens. If all works fine, scratch one.

To eliminate the camera-lens communication, clean up the contacts on the camera mount and lens mount. If all works fine, this was it.

If not, you're left with a lens issue. Tamron lenses have a 6 year warranty, so you should contact them first. If you cannot get warranty coverage, you can either try to open the mount yourself and see if you can figure out the issue, or you can take it to a local camera shop for repair.

[lux-ad-artem]

Good thinking - thanks very much. I'll have to save the testing for another evening - but do you think it's worth fixing if it's a lens issue? Since I got it used, I'm not sure if the warranty is still in effect, but if it is, do ou think it's worth the trouble?

[Laurentiu Cristofor]

Good thinking - thanks very much. I'll have to save the testing for another evening - but do you think it's worth fixing if it's a lens issue? Since I got it used, I'm not sure if the warranty is still in effect, but if it is, do ou think it's worth the trouble?

This is a great lens, so if it was in good working condition before this incident, it is worth getting it fixed as long as it doesn't cost a lot - where you can define "a lot" as a percentage of replacing it with a used one - 30-50%, depending how you feel about it.

But I think there is a great probability you will find this to be a contact issue.

[Pheo]

Mine does this too! Thought it was odd.

[msatlas]

Hmm...I'll have to check this when I get home tonight to see if my 17-50 also behaves this way...

[glasbak]

Mine performs OK.
For the not OK samples, the PCB foil which contains the distance codes is probably not correctly glued in the lens, or the 'fingers' reading the codes are a bit wrong positioned.
Assuming this tamron has a similar distance encoding construction as the AF pentax lenses, not yet disassembled mine.