Topic: AF issues: SOme thoughts and questions

Hey, there.


Long time, no post sad.

Almost no time for taking pictures either sad sad sad...


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 tongue) I believe I had everything set: Cleaned fungus, seated a misaligned element (the lens had obviously been tampered with before wink), 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 tongue...).



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 tongue, but hey...).



Cheers!

Nikon: D7000; F2; F4; FA. RMC Tokina 17/3,5; Ensinor 24/2,8 Macro; Nikkor: S.C. 50/1,4; AI-s 28/2,8; Micro 55/2,8; 80-200/4; S. E: 35/2,5; 100/2,8; Viv. S. 1 105/2,5 Macro (Kiron); MC Rokkor PG 58/1,2; Canon FD 300/4; Pentacon 135/2,8.
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...

Re: AF issues: SOme thoughts and questions

Anyone?





Please smile?

Nikon: D7000; F2; F4; FA. RMC Tokina 17/3,5; Ensinor 24/2,8 Macro; Nikkor: S.C. 50/1,4; AI-s 28/2,8; Micro 55/2,8; 80-200/4; S. E: 35/2,5; 100/2,8; Viv. S. 1 105/2,5 Macro (Kiron); MC Rokkor PG 58/1,2; Canon FD 300/4; Pentacon 135/2,8.
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...

Re: AF issues: SOme thoughts and questions

Most older AF lenses like this Tamron weren't focus adjusted by reprograming, but by solder bridge (e.g. the Canon EF 1.8/50 http://www.youtube.com/watch?v=vOjCiJN7T2E) - if you could find such a bridge on the Tamron's PCB you could try that.

Otherwise you could try to alter the flange distance - many Tamron lenses feature thin spacers under the bayonet. Maybe they are missing because of the earlier attempt?

Re: AF issues: SOme thoughts and questions

Hey, there!

barney wrote:

Most older AF lenses like this Tamron weren't focus adjusted by reprograming, but by solder bridge (e.g. the Canon EF 1.8/50 http://www.youtube.com/watch?v=vOjCiJN7T2E) - if you could find such a bridge on the Tamron's PCB you could try that.


Thanks a bunch! I'll check for that, because I really don't see what else could be wrong...

barney wrote:

Otherwise you could try to alter the flange distance - many Tamron lenses feature thin spacers under the bayonet. Maybe they are missing because of the earlier attempt?


Yes, that's what I've been trying to do. There are no spacers under the bayonet at the moment, only under the rear lens group. According to my "bible", the service manual for the Kiron-made Vivitar Series 1 70-210 (Thanks to the Kiron Kid for posting it - Where are you? Where is everybody? sad), infinity focus at the longer end is adjusted by moving the front lens group away or closer to the camera, and at the wider end is adjusted by moving both the whole lens and/or the rear group away or closer to the camera, by adding/removing spacers.

In my case, I apparently need to add spacers in the rear lens group, or remove spacers from under the bayonet (of which there are none in my case wink). So the only way would be to add spacers to the rear lens group, but I still have to make them up...


Anyway, I'll keep trying: I'll check for the solder bridges (if there are any, I should have no problem fixing that wink), and try to adjust IF with spacers.



Anyway, what we all can make up from this is



MANUAL FOCUS RULES!!!



Cheers!

Nikon: D7000; F2; F4; FA. RMC Tokina 17/3,5; Ensinor 24/2,8 Macro; Nikkor: S.C. 50/1,4; AI-s 28/2,8; Micro 55/2,8; 80-200/4; S. E: 35/2,5; 100/2,8; Viv. S. 1 105/2,5 Macro (Kiron); MC Rokkor PG 58/1,2; Canon FD 300/4; Pentacon 135/2,8.
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...