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08-20-2016, 05:57 PM   #1
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50-135 focus hunting on my K-5

I thought I would share my experience today with my DA* 50-135, in hopes that it might help someone with trouble shooting...


Executive summary:
-SDM seems to be working, driving the focus, but will not lock on.
-Cleaned all contacts
-Verified other lenses
-Tried different lighting situations
-Tried AFS and AFC sincle point, and multiple AF points(manual focus still works)
-Converted to screw drive, lens is now AF again!


Long version

I went to use my 50-135 today, and for some reason it started focus hunting. Back and forth, back and forth, the lens would just not grab focus. I looked at the battery symbol, and it was low. So, I decided to re-charge in hopes the focus hunting would go away ( I only have one battery ).

A few hours later the battery was ready to go, so I popped it in the K-5 and started to test the lens again. Nope, still hunting! Hmm? Is it my camera, do I get to order something new? I figured I should probably test a couple other lenses just to be sure. With a push of the release button, and a twist of the lens, off came the 50-135, and on went the 18-135. Ready to go.

A quick focus on the papers laying on the table, and another of the salt shaker on the counter. Dang, it's not my camera. I went ahead and tested a screw-drive lens just in case. Nope, still not the camera.

Back to Pentax Forums to search for possible root causes, and I came across a couple threads on focus hunting, and saw some suggestions of cleaning the contacts. OK, easy enough. I tracked down the bottle of isopropyl alcohol, and one of my spare eyeglass towels (the free ones that come with every pair of eyeglasses). I cleaned the contacts on the 50-135 and decided I might as well clean the other lenses too (stall tactic).

I'm now ready for the cleaned contact test....and nope. Still focus hunting.

I now have the laptop beside my PC doing multiple searches on both systems. I believe the lights dimmed in the house for a moment, with all the tabs open in chrome.

I tried all the AF methods available. I switched to live view, just to check if that would work. Nada (nothing). I tried AFS, AFC from 50 to 135 and ISO from 80-6400, in the bright sunlight, still nothing.

OK one last check with manual focus. Whew!, I get the focus confirmation in manual. I guess it's time to try the conversion to screw drive. As long as I back-up the lens file I can always convert back to SDM drive.

Woohoo! After some tense moments of seeing my camera in debug mode, the lens is now converted to screwdrive, and the 50-135 is now an AF lens again! Time to take some pictures...

08-20-2016, 06:10 PM   #2
pjv
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QuoteOriginally posted by Riggomatic Quote
the lens is now converted to screwdrive, and the 50-135 is now an AF lens again!

Sorry to hear about your ( another ) SDM issue David, but glad to hear it was an easy fix. Just for interest sake, how noisy do you find the screwdrive? Cheers.
08-20-2016, 07:24 PM   #3
mee
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Mine tends to hunt at 135mm some times. It goes just back of focus and then just forward (crossing actual in-focus each time haha). I just use the quick shift and get it back.. seems to happen most often in lower contrast areas so I am not sure it is the lens.
08-20-2016, 08:41 PM   #4
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QuoteOriginally posted by pjv Quote
Sorry to hear about your ( another ) SDM issue David, but glad to hear it was an easy fix. Just for interest sake, how noisy do you find the screwdrive? Cheers.
Compared to the DFA100mm wr, it's quieter. It must be a faster pitch screw, because it sounds like a higher note, when traveling the focus range.

My only other Pentax screw drive I have is the kit 18-55wr. Seems just a bit quieter than that one too.

I bought this lens used last March, and the seller said it had SDM issues. At least I got to experience the SDM for a few months.

Thanks!

---------- Post added 08-20-16 at 11:59 PM ----------

QuoteOriginally posted by mee Quote
Mine tends to hunt at 135mm some times. It goes just back of focus and then just forward (crossing actual in-focus each time haha). I just use the quick shift and get it back.. seems to happen most often in lower contrast areas so I am not sure it is the lens.
Mine went all at once. I was able to get focus, at 50mm, a couple times today, but not consistently. My failure version must be a runaway SDM.

Best of luck with yours.

08-23-2016, 09:03 AM   #5
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Sounds like it could be a SDM issue. My 50-135 works perfectly and doesn't hunt at all on the K3, however my 16-50 hunts a lot and focusing is very slow. The good news is it is possible to convert these over to screw drive if you don't feel like shelling out the money to get the SDM repaired. Its also possible that its the AF system in the K5, I had one and it used to hunt all of the time with SDM lenses but the screw drive lenses seemed to have better luck, not sure why. I made sure the contacts were clean. I think the K5 had some focusing issues from the get go that were fixed in the K5II update.
08-23-2016, 09:35 AM   #6
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QuoteOriginally posted by GateCityRadio Quote
Sounds like it could be a SDM issue. My 50-135 works perfectly and doesn't hunt at all on the K3, however my 16-50 hunts a lot and focusing is very slow. The good news is it is possible to convert these over to screw drive if you don't feel like shelling out the money to get the SDM repaired. Its also possible that its the AF system in the K5, I had one and it used to hunt all of the time with SDM lenses but the screw drive lenses seemed to have better luck, not sure why. I made sure the contacts were clean. I think the K5 had some focusing issues from the get go that were fixed in the K5II update.
Yup. It was the SDM. When I converted it that day, it worked great. I haven't gone back and checked focus accuracy. That's planned for this weekend.
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