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02-27-2018, 04:27 AM   #1
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50-135 Focus Lock-up - SDM woes?

We are currently touring around Vietnam. Today, I was shooting some long exposures of a waterfall here, and a strange thing happened.

Lens was working just fine, until suddenly it would not focus using autofocus. I put everything to manual and could focus the lens, but noted the ring was stiff.

I first though the worst, that the SDM had died as I know older copies of these were prone to do. However, about an hour later I tried again (after having used a different lens for the hour) and the autofocus worked as normal.

I wondered if heat could be responsible. Of course, materials expand in the heat, and Vietnam has plenty of it. Perhaps said expansion prevented autofocus somehow?

Any thoughts? Is this the first sign of SDM trouble around the corner, or more likely just due to the high temperatures?

Cheers for any advice.

02-27-2018, 06:46 AM   #2
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I'd keep an eye on it. But if it is still relatively quick and doesn't hesitate or miss focus a lot I'd not worry too much.
02-27-2018, 07:00 AM   #3
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I've had my DA*50-135/2.8 give up on AF a few times before I converted it to screw drive (see thread on this in this section of the forum).

However, I've always been able to focus manually when that happened. No stiffness whatsoever... I once went almost 3 weeks on manual focus after which it suddenly started AFing again... My experience has made me believe that humidity may have an influence. For instance, those three MF weeks were spent in Nicaragua, which was much more humid than my normal residence in Belgium.

My DA*50-135/2.8 has always come back to life again (contrary to my DA*16-50/2.8). I have both converted to screw drive now, and have since never experienced any failure of AF.

Good luck!!

Wim
02-27-2018, 09:15 AM   #4
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QuoteOriginally posted by dMwBennn Quote
but noted the ring was stiff.
This part makes it sound like something other than SDM issues. I've not heard of anyone experiencing a similar issue when the lens had an SDM problem.

I would lean more towards a bit of grit in something or just uneven expansion due to the heat.

02-27-2018, 10:12 AM   #5
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sometimes it is just a problem between Quickshift and AF gears. If you turn a little bit the screw AF and when it works again it has nothing to do with the SDM. Than it was just a mechanical issue. The stiffness you taked about is a sign for this kind of behaviour.
02-27-2018, 07:04 PM   #6
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Thanks for the replies.

I hope it either 1) is something more heat/humidity related (Vietnam also has humidity in spades, just like Nicaragua, so could be!) or 2) it lasts for the next few months so I don't have to think about conversion until back in the UK!

Will have a read up on converting to screw drive down the road, as I'd be fine with that solution.
02-27-2018, 10:12 PM   #7
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What older camera bodies do you have?
02-28-2018, 08:00 PM   #8
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Hi, I have the K-3 and my girlfriend has a K-5.

Are you able to convert to screw drive with the K-5, do you know?

03-01-2018, 11:41 AM   #9
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QuoteOriginally posted by dMwBennn Quote
Thanks for the replies.

I hope it either 1) is something more heat/humidity related (Vietnam also has humidity in spades, just like Nicaragua, so could be!) or 2) it lasts for the next few months so I don't have to think about conversion until back in the UK!

Will have a read up on converting to screw drive down the road, as I'd be fine with that solution.
Mine works like a charm again with the screw drive conversion.
03-01-2018, 12:16 PM   #10
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QuoteOriginally posted by dMwBennn Quote
Hi, I have the K-3 and my girlfriend has a K-5.

Are you able to convert to screw drive with the K-5, do you know?
As I understand it - the answer is YES, but it may require PKTether to do this. I am not the expert but I can help look into this if you need help finding the info. Let me know.

EDIT: You may be able to use the standard DEBUG menu mode if you can get the files in this place for the K-5 to work:

Dropbox - enable Debug Menu[COLOR="Silver"]

---------- Post added 03-01-18 at 02:21 PM ----------

How To: Convert SDM to ScrewDrive + Video - PentaxForums.com (how to video)

---------- Post added 03-01-18 at 02:28 PM ----------

More details: How to deactivate SDM and allow for screw drive autofocus with DA* 16-50mm f/2.8 - Page 19 - PentaxForums.com

Also several people report being able to use the K-5 / K-5ii series with the debug files on the SDCard and doing this WITHOUT using PKTether. Doing it this way is similar to any other camera that can boot from file on the SD card. The files are maintained on that dropbox listed earlier.
03-02-2018, 12:17 AM   #11
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That looks great, thanks for the info. Who knows maybe this was a one off problem!

That said, at least I have good info to turn to now so that if it does die on me, I can stop off at an Internet cafe and sort it.

Cheers.
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