DA* 50-135 focus issue


Aero

Link Posted 13/03/2021 - 15:24
Hi, folks. I'm in a bit of a quandary over my DA* 50-135. It started failing to lock focus at 135mm or slightly below, although it was fine at other FLs. This seems to relate to an SDM issue and I was getting ready to post it to Pentax repair in France (where I live) when the problem disappeared. I've been testing it for a week now and focus locks properly and quickly at all FLs. Admittedly, I hadn't been using the lens much but the same problem cropped up a year ago when it saw regular action at least once a week.

I'm concerned (and fairly confident) the problem will return when I'm relying on the lens later this year at some music gigs. It strikes me there's no point sending it in for repair while it's working properly. I suppose I could describe the problem and hope for the best, but this wouldn't be ideal. Any advice on the best way forward? I looked into switching it to screw drive but all the information on the net was quite old and some of the required software doesn't seem to be available from a reliable source any more. I'd appreciate any wisdom you can offer.
Last Edited by Aero on 13/03/2021 - 15:25

pschlute

Link Posted 13/03/2021 - 15:34
I never owned that lens but did have a DA* 16-50 which had lazy AF. I used to start up by manually focussing to the extremes a few times, then turn on the AF and make the thing focus from both extremes to a point in the middle ground a few times. Once done it worked fine for the photo session. Next time, same procedure.

As far as sending your for repair I would say don't bother. You are likely to get it back a number of weeks later with a note saying "no fault found".
Peter



My Flickr page

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Aero

Link Posted 13/03/2021 - 17:43
Thanks, Peter. I'll try your system for a while and keep my fingers crossed.

Pwynnej

Link Posted 13/03/2021 - 19:49
Sounds like you have something with AI installed... always when threatened with mechanic the symptoms miraculously disappear...our old Golf was a pig until it got onto the road the VW garage was, then it ran perfectly.

Is the problem with AF at low light? It's been a problem with my lenses and the lens hunts (not limited to DA* glass either). If SDM works on other occasions it doesn't sound like the SDM motor but maybe the sensitivity of the AF sensor...

Battery maybe?

Let's hope you get to the bottom of it by the time the gigs come around.
Z-1p, K-1, P50
F50 1.7. FAs 24, 35, 50 1.4, 85, 135. DFA15-30, DFA24-70, D-FA*70-200. D-FA 100. DA*300. TC 1.4. The SMC-FA Limited Trinity.
Metz 45 CL-4, AF500FTZ. AF540FGZ.
Some Mamiya and some Nikon
Last Edited by Pwynnej on 13/03/2021 - 19:52

Aero

Link Posted 13/03/2021 - 21:22
Pwynnej wrote:
Is the problem with AF at low light? It's been a problem with my lenses and the lens hunts (not limited to DA* glass either). If SDM works on other occasions it doesn't sound like the SDM motor but maybe the sensitivity of the AF sensor...

Battery maybe?

Light level made no difference. What I can't understand is why it would hunt only at maximum zoom or thereabouts. Knock it back a few millimetres and it would work normally. I made sure to test it with full batteries. My old Peugeot 307 did the same as your VW. Luckily, the problems disappeared when it spontaneously combusted in a car park

Mike-P

Link Posted 19/03/2021 - 07:38
Aero wrote:
Knock it back a few millimetres and it would work normally.

The 17-70mm is well known for developing the same fault. That problem is the SDM motor.
. My Flickr

Jonathan-Mac

Link Posted 19/03/2021 - 08:42
The repair people will know very well what the problem is, having seen it probably thousands of times before. They will be able to replace the faulty parts even if the problem isn't manifesting itself at the time the lens gets to them.
Pentax hybrid user - Digital K3 & K200D, film 645 and 35mm SLR and Pentax (&other) lenses adapted to Fuji X digital
Fan of DA limited and old manual lenses

Aero

Link Posted 20/03/2021 - 21:04
Many thanks, chaps. Off to the repair shop it goes.

Aero

Link Posted 28/04/2021 - 15:40
Quick update: the French repair people, PM2S, are fixing it for the equivalent of 180. I think that's money reasonably well spent if the repair holds up for a while. Thanks again for your advice.
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