[Jon]

So I purchased a cosmetically great, lightly used version of the Tammy 70-200/2.8 Di LD IF Macro. (for use on a K-3)
I was concerned about focus issues from the research I did prior to the purchase, but the price basically made it a consequence free purchase as I can eBay it for as much or more than I paid. So in just a couple hours of use, my fears were realized. I first thought it was a front focussing issue, so I did the focus adjustment in body. However, the issue is not consistent. It is as if the Lens is lazy. It's accurate, maybe 1/3 to 40% of the time. The other times is just settles for close enough. On a f/2.8 tele used for portraiture, this is easily detectable and just not acceptable. I plan to use the lens through the next week to make sure it is an ongoing issue.

My questions for the Forum are two fold.
First: This issue is well documented, but no one has been able to reveal a solution other than return it and hope your next one is better. Has Tamron acknowledged this issue and can they fix it?
Second: Whats are our other options in this lens category? The DA 50-135 is shorter than I want and the focus and SDM issues have scared me away from it. Thus, is our only reasonable option the current $1250 Sigma 70-200/2.8? Does anyone have another comparable lens they could recommend if I opt to sell this one?

Thanks in Advance.

[mikeSF]

In that price range, I would try to get a better copy of the Tammy. It is a very fine lens when working properly. My first one had a focus issue but the replacement was spot on.

[Jon]

^Were you encountering similar issues with your first copy? Also, how good is your second one AF performance wise? Does it still struggle in low contrast areas?
I feel I may not have a bad copy, I might just be holding the lens to a standard I shouldn't.
I have doing more tests and noticed that when the lens is set to a further distance prior to attempting AF, it has a higher success rate of hitting the focus. Also, if the lens is currently set to a focus distance that is anywhere near the desired AF distance it just accepts it as being in focus, when in fact it is not.

[mikeSF]

No, my issue was not anything like yours, my first copy was front focusing at the short end of the zoom and back focusing at the long end, so the in camera adjustment could not solve it. The new copy performs perfectly pretty much every time. Your question about low contrast seems like you may be expecting too much of your camera, as I believe the limitation may be the camera not the lens. I have not read any similar accounts to the issue you've described and recommend you replace it altogether.

[mikeSF]

Has anyone suggested you may have a loose nut behind your camera??

[Jon]

From DPReview....
One problem we encountered with this lens in real-world shooting was a higher than expected proportion of slightly defocused images, especially visible when shooting at F2.8 where the depth of field can be extremely shallow. This was not a systematic 'front-focus' or 'back-focus' problem, but instead an apparently random tendency to miss focus slightly in situations for which we would normally expect a 100% hit rate. This issue persisted across a variety of camera bodies, from the EOS 450D through to the EOS-1D Mark III, so we can only conclude that it is a problem with the lens itself.

[TopherTheME]

My copy behaves the same way as the DPReivew describes. It often front focuses but sometimes it back focuses on my K-5. On my K-01 its always way off and makes it nearly unusable with that body. I believe this is due to a relatively short throw for the internal focus. The body just doesn't have enough resolution in the motor to achieve an accurate focus. My solution to this was to try and focus on high contrast areas, and to take lots of shots. After using the lens for a while and getting familiar with how it behaves I've been able to get pretty decent AF performance out of it. Now the only problem I really have is that the AF is loud and slow.

I also own the DA* 50-135 and purchased it thinking it would replace the Tammy, but in reality its really a different lens. The 50-135 is lighter, smaller, and has better AF performance (not by much, but it is accurate). But on the other hand I really miss that extra 75mm of reach when doing wild life photos and that really close focus distance, so it usually stays at home and will probably be up for sale soon. Personally, I wouldn't really worry about the SDM issue as its a problem that only seems to have manifested in a small sample of lenses. Chances are if you buy a used copy thats a few years old it wont develop any SDM issues.

[Jon]

^Thanks Topher, Cheers.