So, i've just picked up an old Tamron AF 20-40 F2.7-3.5 SP. From the mid '90's i guess. I wanted a zoom covering that focal length on full frame and this one was old new stock and very cheap so i figured it would be worth a try particularly considering some of the rave reviews about it to be found online (always taken with a pinch of salt of course). When i first put it on the d700 it turned out the focus was a bit of a mess. Extremely soft and mushy at pretty much all lengths and stopping down didn't help a huge amount. Anyway, i figured it was front or back focussing so did a few tests and adjusted the AF fine-tune on the camera and pretty much got it spot on. At AF +20 it is great at all lengths wide open. I'm very happy with it.
Trying the same on my d300, though, hasn't really helped. It's the wide-mid end which is a mess. No amount of AF fine tuning seems to help. At 35mm it is fine and sharp and, interestingly, if i zoom out to 20mm and shoot without re-focusing that is excellent as well. As soon as i refocus it jumps all out and turns to mush. Bit annoying. Any thoughts? |
