I am chasing a black cat in a pitch black room, and so far I can’t rule out that it’s metaphysical.
Fact is, that I have the feeling that the new Tamron SP AF 17-50mm 2.8 XR Di II VC LD Asp IF performs not as well as it could, at least in the autofocus department. The only hard fact is, that the lens sometimes does not focus. Turn the camera off, turn it back on, everything is OK. It does not happen all the time it does not happen every second, third, or whatever-th time, but it sure happens every now and then.
So far Earl has contributed that his Tamron 28-300 behaves just as my 17-50. This may be a Tamron problem after all. On the other hand, it may be not. We are still far from having a statistically relevant sample.
I have an idea. I will compare this lens set to 35mm with the Nikon 35/1.8. I will make the comparison at f2.8, an aperture that both lenses are capable of. I will test different AF points, focusing from infinity to a certain target, the same from very near to that target, making the images without checking, just as one would in action, repeat 10 times for every lens and point and focusing way. Then I’ll count the perfectly focused vs slightly focused vs unfocused images and compare by lens. This is pretty tedious and I’ll need good light, thus it needs to wait for the weekend, but it will give me a clue about the general AF performance and accuracy of this lens.
I expect though, that my the results will support my current feeling: When it focuses, it focuses very accurately, at least that’s what I can say about the center AF point, the one that I use most often.
The other problem is, that when you’re trying to track down such a problem, you quickly begin to see ghosts. Take yesterday: I suddenly found that it did not focus at all. Oh dear, now it’s broken, I thought, but in reality I had accidentally set the camera to manual focus 🙂