Photoclubalpha

Well first off i done the adjustment last year and at the time it seemed to help out. But now pretty my exactly one year on i have focus issues at longer focal lengths. I mean really really bad @ 400mm i almost never hit accurate focus at anything over 40m.

Would a poorly (DIY) adjusted AF module be much worse the longer the focal length?

At the time when i done the adjustment i was well prepared or so i thought, i had a 360 deg. angle measure with a 2mm whole in the centre with a rotating rule to get each turn on the hex screws exactly the same. But one of the screws had the thread lock very tight and it span out with the key jumping out the slot! So that was the accurate adjustment gone.

Also i was surprised at just how free the screws would rotate, i would in all honesty expect the screws to shift with regular vibration.

Iam at the stage (probably tomorrow) where i shall screw them all tight and start again properly adjusting them equal amounts.

In reality i can get a sharper shot @200mm cropped than i can ever get @ 400mm. As you can imagine its really starting to bug me now.

My thoughts are try fix it agian DIY from scratch and if all else fails send it in.

It just seemed strange to be so bad at longer focal lenghts?

I think these screws are never menat to be tight as there should be a zero point inthis system. and if you were adjusting this before with large apertures and bad lights then yeah it's likeky the focus is not correct

I know its been off for a while i suppose but work has halted me getting out this year, when spot focusing i know its off, to the right and down a bit.

I just didnt expect it to be so so bad with one lens. The Sigma 120-400mm HSM. When i saw the recall i thought thats the problem but my lens serial number is a good bit off the recall numbers.

Well after a almost a whole year getting more & more frustrated using the Sigma 120-400mm HSM i finally got to the bottom of the problem, It was my AF module adjustment. It was out by a massive amount on probably every axis!

How did i manage to get it so wrong i dont know. Trouble is i was using a few primes & the tamron 17-50mm alot also which when stopped down did not really exibit the same problems.

I was in a bit of a mood last week and thought iam going to get to the bottom of this as the Sigma 120-400mm has been out since the day i bought it at anything over 30-40mt. So i did every focus test i could find and they appeared not to bad indoors but as soon as i went out the lens was terrible.

So i screwed the AF module fully home carefully and started from scratch with the proper tools. (Engineering Background)

I had thought manual focus would cure AF problems but NOT if the module is out which surprised me.

After about 10 mins and a few snapshots later the lens is now almost spot on. I also tested the Minolta 50mm, Tamron 17-50mm, Tamron 55-200mm, Minolta 100-200, Minolta 70-210mm, Minolta 35-70mm, Minolta 35-105mm, 100mm Macro, Minolta 28mm.

All but the Macro were showing about 30cm Backfocus at around 4mt The 100mm Macro always appears spot on whatever i do to the AF module!
Cant believe i put up with this for almost a year!!

Well that's good news. You have your camera sort of upgraded.

I've also had problems with the AF module (skewed). I have also reset it and started all over. First I adjusted for BF/FF and now I'm in the process of adjusting pitch and yaw. Does anyone have any tips on the best way to get the AF module to line up precisely with the AF sensor?