Pentax 50-135 SDM Focus hunting

Seb · 11-15-2017, 11:45 PM

Dear PF-Community,

I've bought a used 50-135 lens which is i a decent condition with no scratches or stuff like this.

Unfortunatly I haven't had the opportunity to try it in natural light as I start working in the dark and come home in the dark. Today I take my camera to work.

My Problem: With my K5 the af (Center spot, AF-S) is terribly hnuting in artificial light. Sometimes it hunts from the long end to the short and back, but most of the time its like an iteration. It goes a little bit behind the sharp setting and then goes a little bit back in front of the sharp setting. It feels like the steps are getting a little bit smaller every time. It takes like 6 steps to finaly bring the 'confirmation-beep' from the K5. Then the image is very sharp and in focus!

Edit: Sometimes it takes 2 attempts of half pressing the shutter as it simply stops beeing not in focus.

Is this a normal behaviour of the 50-135 with K5 in low/artificial light?

I had a SDM-Failure with a 16-50 once that was a little different. The motor simply refused to work after switching on the camera. But here it doesn't hesitate.

I'm looking forward to reading your suggestions!

Have a nice day

Sebastian

Reed · 11-16-2017, 01:27 AM

Check if your camera firmware is up to date.

D1N0 · 11-16-2017, 03:34 AM

The K-5 isn't a very quick focusser in low light. Maybe try it in daylight conditions or under strong artificial lighting. The DA 50-135 is also not known for speedy focussing.

Seb · 11-16-2017, 05:35 AM

Thank you for the replies!

I have the latest Firmware 1.16. I tried the AF during my lunch break and it is definately much better in day light. This "iteration" kind of thing is still there.

I don't know how the combination Camera <-> lens exactly works, but I guess the impulse to start and stop the motor comes from the k5. Is it possible that a defective AF-motor doesn't stop precisely enough?

Tonight I will do a test with a K-S1 and report afterwards.

Sebastian

Reed · 11-16-2017, 05:52 AM

It is possible that if not used , SDM contacts in your camera got patinated a bit and there are some dissruptions in the current, try to rub them and both lens mount contacts with technical alcohol(IPA or somthing simmilar).

**Eagle94VT** · 11-16-2017, 05:56 AM

My SDM is blown on my 50-135. But even when it was up and running it wasn't great - I could take a sip of coffee while it tried to lock on. I've opted to use it only in manual mode instead of a repair. I don't use it much, and its not the lens I take out on outdoor adventures.

**UncleVanya** · 11-16-2017, 07:23 AM

As a person who has seen a lot of SDM lenses in their decline, I can tell you I have seen a couple 50-135 lenses acting similarly that were cured by conversion to screwdrive.

I was sceptical at first when a customer asked me to convert an otherwise working lens that had trouble locking focus - particularly in poor lighting. However we tried it and it worked! It was night and day - the theory being that failing SDM wasn't precise and overshot or undershot the fine adjustments. Ultimately you might want to try converting the lens to see if that makes a difference.

**AlwaysAl** · 11-16-2017, 08:45 AM

Had a similar experience, bought a used 50-135 (for use with a K-20 or a K-5IIs) and unless the light was "outside perfect" it struggled (with many iterations) to get focus. At times, even when it did seemingly achieved focus, the image produced wasn't crisp therefore making the lens an unreliable item for my kit (just another brick). Like yourself tried to find a work-around without an operationally consistent success (a roller coaster ride of jubilation and despair). Finally out of that desperation and what appeared to be a deteriorating condition, bit the bullet and took it in for repair. Basically, the shop immediately diagnosed and replaced the motor.
Thanks to this Forum, I was aware of the motor issues with this lens series and the previous owner provided documentation showing the motor had been replaced under warranty. Due to this fact, it never occurred to me that I could be experiencing the symptoms of second motor failure. Upon reflection, perhaps I was also struck with a broad-stroke mental image that motor failure equated to "no rotation" without a thought there may be an integral electronic control mechanism that packs up. Since the repair, the lens is "snappy" when focusing and has become a joy to use (I think even better than my DA*55).

Seb · 11-17-2017, 12:53 AM

Wow, what a great support here. Thanks!

Well, I cleaned the contacts with no success. The lens behaves the same way on K-S1.

I haven't had time to do the screw drive hack, but contacted the seller instead.

She was not amused but offered me a refund.

I paid 420 € for a 2013 lens. Bite the bullet and use screw drive or send it to Pentax (about 300 € if they change the motor)? Leave the sinking ship and send it back to the seller?

What would you do?

D1N0 · 11-17-2017, 01:50 AM

Try to get a partial refund and get it repaired. 720 is a bit to much for what would be a refurb. Shops sell occasions with limited warranty for about 650.

Seb · 11-17-2017, 05:51 AM

I've done a little internet research. New prize is around 1.000 € display models are about 100 € cheaper. On ebay are some refurbished ones with limited warranty starting from 600 €. I would have to ask for the date of manufacture then.

I don't think the seller will give me any partial refund as we had a slight argument about my complaints.

Now it's my turn to decide. ;-)

**UncleVanya** · 11-17-2017, 06:52 AM

Seb what camera are you using for conversion? Generally speaking it is a simple conversion and the lens is pretty snappy afterwards.

Seb · 11-17-2017, 07:30 AM

I'm using a K5. I think i keep the lens. Its a very sharp copy even at 135 mm wide open. The only thing that keeps me from conversion is the AF-noise. I plan to shoot a wedding next year. But there is still enough time to send it to Ricoh if it is too noisy.

**UncleVanya** · 11-17-2017, 07:33 AM

Originally posted by Seb

I'm using a K5. I think i keep the lens. Its a very sharp copy even at 135 mm wide open. The only thing that keeps me from conversion is the AF-noise. I plan to shoot a wedding next year. But there is still enough time to send it to Ricoh if it is too noisy.

Several people have used the K-5 for conversions so I know it can be done. I have converted dozens and i can tell you the DA* sealed lenses are much quieter than the consumer zoom DA 55-300 as an example. The lens will be a bit louder but it is not obnoxious as I see it. I don't shoot weddings but many were shot back in the day when no one had silent motors without anyone being upset - I would hope that wouldn't cause issues but only you know your clients.

TheOneAndOnlyJH · 11-17-2017, 08:23 AM

I can't say if mine is a good or bad example, but my lens goes back and forth a bit before locking focus too. I definitely wouldn't say it's a fast focusing lens design, but before you decide you might want to upload a video that shows the focus ring turning on the lens as you lock on. That way people can tell you if it looks faster or slower than theirs better than written descriptions.

11-15-2017, 11:45 PM	#1
Seb Junior Member Join Date: Jan 2016 Location: Wuppertal, Germany Posts: 35	Pentax 50-135 SDM Focus hunting Dear PF-Community, I've bought a used 50-135 lens which is i a decent condition with no scratches or stuff like this. Unfortunatly I haven't had the opportunity to try it in natural light as I start working in the dark and come home in the dark. Today I take my camera to work. My Problem: With my K5 the af (Center spot, AF-S) is terribly hnuting in artificial light. Sometimes it hunts from the long end to the short and back, but most of the time its like an iteration. It goes a little bit behind the sharp setting and then goes a little bit back in front of the sharp setting. It feels like the steps are getting a little bit smaller every time. It takes like 6 steps to finaly bring the 'confirmation-beep' from the K5. Then the image is very sharp and in focus! Edit: Sometimes it takes 2 attempts of half pressing the shutter as it simply stops beeing not in focus. Is this a normal behaviour of the 50-135 with K5 in low/artificial light? I had a SDM-Failure with a 16-50 once that was a little different. The motor simply refused to work after switching on the camera. But here it doesn't hesitate. I'm looking forward to reading your suggestions! Have a nice day Sebastian

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11-16-2017, 01:27 AM	#2
Reed Pentaxian Join Date: Mar 2015 Location: Warsaw Photos: Gallery Posts: 638	Check if your camera firmware is up to date.

11-16-2017, 03:34 AM	#3
D1N0 Pentaxian Join Date: May 2012 Location: --- Photos: Gallery Posts: 6,802	The K-5 isn't a very quick focusser in low light. Maybe try it in daylight conditions or under strong artificial lighting. The DA 50-135 is also not known for speedy focussing.

11-16-2017, 05:35 AM	#4
Seb Junior Member Join Date: Jan 2016 Location: Wuppertal, Germany Posts: 35 Original Poster	Thank you for the replies! I have the latest Firmware 1.16. I tried the AF during my lunch break and it is definately much better in day light. This "iteration" kind of thing is still there. I don't know how the combination Camera <-> lens exactly works, but I guess the impulse to start and stop the motor comes from the k5. Is it possible that a defective AF-motor doesn't stop precisely enough? Tonight I will do a test with a K-S1 and report afterwards. Sebastian

11-16-2017, 05:52 AM	#5
Reed Pentaxian Join Date: Mar 2015 Location: Warsaw Photos: Gallery Posts: 638	It is possible that if not used , SDM contacts in your camera got patinated a bit and there are some dissruptions in the current, try to rub them and both lens mount contacts with technical alcohol(IPA or somthing simmilar).

11-16-2017, 05:56 AM	#6
Eagle94VT Site Supporter Join Date: Dec 2010 Photos: Albums Posts: 291	My SDM is blown on my 50-135. But even when it was up and running it wasn't great - I could take a sip of coffee while it tried to lock on. I've opted to use it only in manual mode instead of a repair. I don't use it much, and its not the lens I take out on outdoor adventures.

11-16-2017, 07:23 AM	#7
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,472	As a person who has seen a lot of SDM lenses in their decline, I can tell you I have seen a couple 50-135 lenses acting similarly that were cured by conversion to screwdrive. I was sceptical at first when a customer asked me to convert an otherwise working lens that had trouble locking focus - particularly in poor lighting. However we tried it and it worked! It was night and day - the theory being that failing SDM wasn't precise and overshot or undershot the fine adjustments. Ultimately you might want to try converting the lens to see if that makes a difference.

11-16-2017, 08:45 AM	#8
AlwaysAl Loyal Site Supporter Join Date: Mar 2007 Location: West GTA, Ontario, Canada Photos: Gallery \| Albums Posts: 555	Had a similar experience, bought a used 50-135 (for use with a K-20 or a K-5IIs) and unless the light was "outside perfect" it struggled (with many iterations) to get focus. At times, even when it did seemingly achieved focus, the image produced wasn't crisp therefore making the lens an unreliable item for my kit (just another brick). Like yourself tried to find a work-around without an operationally consistent success (a roller coaster ride of jubilation and despair). Finally out of that desperation and what appeared to be a deteriorating condition, bit the bullet and took it in for repair. Basically, the shop immediately diagnosed and replaced the motor. Thanks to this Forum, I was aware of the motor issues with this lens series and the previous owner provided documentation showing the motor had been replaced under warranty. Due to this fact, it never occurred to me that I could be experiencing the symptoms of second motor failure. Upon reflection, perhaps I was also struck with a broad-stroke mental image that motor failure equated to "no rotation" without a thought there may be an integral electronic control mechanism that packs up. Since the repair, the lens is "snappy" when focusing and has become a joy to use (I think even better than my DA*55).

11-17-2017, 12:53 AM	#9
Seb Junior Member Join Date: Jan 2016 Location: Wuppertal, Germany Posts: 35 Original Poster	Wow, what a great support here. Thanks! Well, I cleaned the contacts with no success. The lens behaves the same way on K-S1. I haven't had time to do the screw drive hack, but contacted the seller instead. She was not amused but offered me a refund. I paid 420 € for a 2013 lens. Bite the bullet and use screw drive or send it to Pentax (about 300 € if they change the motor)? Leave the sinking ship and send it back to the seller? What would you do?

11-17-2017, 01:50 AM	#10
D1N0 Pentaxian Join Date: May 2012 Location: --- Photos: Gallery Posts: 6,802	Try to get a partial refund and get it repaired. 720 is a bit to much for what would be a refurb. Shops sell occasions with limited warranty for about 650.

11-17-2017, 05:51 AM	#11
Seb Junior Member Join Date: Jan 2016 Location: Wuppertal, Germany Posts: 35 Original Poster	I've done a little internet research. New prize is around 1.000 € display models are about 100 € cheaper. On ebay are some refurbished ones with limited warranty starting from 600 €. I would have to ask for the date of manufacture then. I don't think the seller will give me any partial refund as we had a slight argument about my complaints. Now it's my turn to decide. ;-)

11-17-2017, 06:52 AM	#12
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,472	Seb what camera are you using for conversion? Generally speaking it is a simple conversion and the lens is pretty snappy afterwards.

11-17-2017, 07:30 AM	#13
Seb Junior Member Join Date: Jan 2016 Location: Wuppertal, Germany Posts: 35 Original Poster	I'm using a K5. I think i keep the lens. Its a very sharp copy even at 135 mm wide open. The only thing that keeps me from conversion is the AF-noise. I plan to shoot a wedding next year. But there is still enough time to send it to Ricoh if it is too noisy.

11-17-2017, 07:33 AM	#14
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,472	Originally posted by Seb I'm using a K5. I think i keep the lens. Its a very sharp copy even at 135 mm wide open. The only thing that keeps me from conversion is the AF-noise. I plan to shoot a wedding next year. But there is still enough time to send it to Ricoh if it is too noisy. Several people have used the K-5 for conversions so I know it can be done. I have converted dozens and i can tell you the DA* sealed lenses are much quieter than the consumer zoom DA 55-300 as an example. The lens will be a bit louder but it is not obnoxious as I see it. I don't shoot weddings but many were shot back in the day when no one had silent motors without anyone being upset - I would hope that wouldn't cause issues but only you know your clients.

11-17-2017, 08:23 AM	#15
TheOneAndOnlyJH Veteran Member Join Date: Dec 2013 Location: Buffalo, NY Posts: 351	I can't say if mine is a good or bad example, but my lens goes back and forth a bit before locking focus too. I definitely wouldn't say it's a fast focusing lens design, but before you decide you might want to upload a video that shows the focus ring turning on the lens as you lock on. That way people can tell you if it looks faster or slower than theirs better than written descriptions.