Topic: AF issues: SOme thoughts and questions
Long time, no post .
Almost no time for taking pictures either ...
Anyway, here's the deal: Got a Tamron AF 20-40 some time ago, second hand. Cheapish, as it had a lot of "issues", which I thought I might manage to fix.
OK, after a couple of tries (in a long time span of about a year ) I believe I had everything set: Cleaned fungus, seated a misaligned element (the lens had obviously been tampered with before ), and fixed a reversed dublet. No deal: the wide open shots were always very, very soft, becoming acceptable by f-5,6, f-8. Then I realised that it was "only" misfocusing: I squated and shot a piece of ground (at an angle) and there it was, the center of the image (where I "told" the camera to focus) was very soft, but the very lower edge of the image was OK (at 20 mm, f-2,7).
Then I tried it manually (manual focus) and got the same results. THEN, I tried it REALLY manually (disconnected the electronics and worked as an AI lens - I'm using a Nikon D90 camera, BTW), and I got MUCH better results.
My conclusion: The electronics are at fault, there is no optical reason for this focus problem.
I still have to check this more thoroughly, but this seems about right. So, my question is, is there any way to fix this?
I mean, short of replacing or reprogramming the electronics, from what I've read elsewhere, focus recalibration for lenses involves this reprograming...
My camera has no AF compensation, so that's not an option (also, It's so far off I'd doubt a camera with such compensation would be enough to fix the problem ...).
I see nothing else that can be wrong, even in the electronics inside, which do not appear to have been tampered...
Any help would be appreciated (I know this is the Manual Focus Forum , but hey...).
Pentax: K20D; CZJ Flek 20/4; SMC Pentax: A 28/2,8; 50/1,7; M 50/1,4; Tak. 50/1,4; Tamron Adall 2: SP 90/2,5 Macro; SP 60-300; 35-70/3,5 CF; .
And some others...