[naomi.mavro]

Hi everyone,

I recently bought DA* 50-135mm lens from ebay. The lens looks new and untouched but the SDM is very tricky: at start the AF is dead completely, I can use it only on MF. If I turn the camera to LiveView slowly the AF starts to work and than I can switch to Viewfinder and AF is fully functional, but the minute I turn the camera off AF dies again and I have to repeat the procedure (LiveView and so forth..). Since this is my first encounter with a SDM motor I don`t know what to believe of it: is it broken? discharged? stuck? what could cause this problem?. I have to mention that I use it on a K3 and I am very satisfied with the accuracy of the AF and that I have tried several times to charge the lens capacitor leaving the camera open but I had no success. I would greatly appreciate any help coming from you. Thank you in advance for you replies. Naomi

[UncleVanya]

First try exercising it a bit. My 50-135 was advertised as dead sdm, but after rapidly spining the focus ring back and forth for greater than five minutes it unstuck itself and has worked ever since. However, if that doesn't work you could try cleaning the lens mount and body contacts.

If none of that works you can convert it to screw drive. I recently converted another forum member's lens, a video of what the focus looks like and sounds like is in this thread: https://www.pentaxforums.com/forums/24-photographic-equipment-sale/311609-sal...nversions.html

If you need help and prefer to convert this on your own, there are many threads that detail the SDM conversion process. This it's a chaotic one but probably the most comprehensive: https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/208353-how-deactivate-sdm-allow-screw-drive-autofocus-da-16-50mm-f-2-8-a.html

[aleonx3]

My personal experience with the SDM lens is not to keep the lens in horizontal position (that means remove from camera when not being used), keep the lens standing upright face down. I have not experienced any problems any time when I need to use the lens. I don't know enough whether it is due to the design of the SDM motor vs Canikon's ring motors, but it works for me, and of course, YMMV.

[JohnX]

My personal experience with SDM is 'use it, or lose it'.

I have had no problems with any of my SDM lenses, including the 50-135, largely, I hope, due to the fact that I exercise them once a week. I just mount the lens and spend a few minutes focussing on objects at close, medium and long distances, in no particular sequence.

On the other hand, maybe it's just luck?

[naomi.mavro]

I tried to spin the focus ring back and forth but I am not sure that I do it right: I do it in MF - and it turns very smoothly with no resistance from 1 to infinity, (I did not try to go beyond because I do not want to broke anything). I also clean the lens mount and body contacts with no success. Also I noticed a squeak sound when the Af is in function.
Thank you for your offer but since I live in Romania- Eastern Europe I don`t think is possible ...

[UncleVanya]

I tried to spin the focus ring back and forth but I am not sure that I do it right: I do it in MF - and it turns very smoothly with no resistance from 1 to infinity, (I did not try to go beyond because I do not want to broke anything). I also clean the lens mount and body contacts with no success. Also I noticed a squeak sound when the Af is in function.
Thank you for your offer but since I live in Romania- Eastern Europe I don`t think is possible ...

Happy to help talk you through it. Let me know what cameras you have access to and we can walk you through the basics.

---------- Post added 01-16-16 at 06:21 PM ----------

Spin it fast as far as you like. It is ok to go past the normal stops.

[LeDave]

Having owned a 16-50 and 50-135 bought at the same time, 4 years ago, my 50-135 is flawless. However the 16-50 has shown signs of failure. I've revived my 16-50 for awhile now. I found there are two ways to do it,

Twist the barrel quickly left to right, doing a full circle spin on left then full circle spin on right. You may press on the AF button and release for every turn,

or, you can just press the AF button with the 16-50 mounted, Pressing AF button every 3 seconds and then release the AF button, then press AF button again, repeating. Eventually the SDM will start to spin again.

Whichever method you choose, patience, it may take a few minutes to a couple minutes for the SDM to work again.

[jddwoods]

My personal experience with SDM is 'use it, or lose it'.

I have had no problems with any of my SDM lenses, including the 50-135, largely, I hope, due to the fact that I exercise them once a week. I just mount the lens and spend a few minutes focussing on objects at close, medium and long distances, in no particular sequence.

On the other hand, maybe it's just luck?

I Agree 100%. I have 2 SDM lenses: DA 17-70 and DA* 200. If you do not use them at least one a week (DA17-70) or once a month (DA*200) the SDM will not work, at least not right away. I do not know if the DC motor lenses are like this as well, but I do find this to be a nuisance. One time I had given up completely on the DA 17-70 when it did not work for several hours and I assumed the SDM motor finally failed. After about 5 hours of shooting using quick shift to focus manually, it suddenly came to life. Now I exercise it at least twice a week and that seems to keep it working.

[naomi.mavro]

Ok, thank you everyone for tips and help. Obviously the SDM is not dead and with a little effort I managed to make it work. My concern right now is about the AF noise (soft squeak sound) will it go away? Is not harmful for the lens motor? Why does the AF dies every time I shut down my camera? Is it normal?

[UncleVanya]

Ok, thank you everyone for tips and help. Obviously the SDM is not dead and with a little effort I managed to make it work. My concern right now is about the AF noise (soft squeak sound) will it go away? Is not harmful for the lens motor? Why does the AF dies every time I shut down my camera? Is it normal?

In order:
Sounds like that seem to be indicative of failing SDM motors. They don't tend to go away until the motor dies. The sound could indicate additional friction somewhere but no one has ever reported a way to eliminate other than to have the SDM replaced or switch to screwdrive. The AF failing when you turn off the camera is new - I haven't seen that particular failure mentioned before.

Typically the squeek the slow response the failure with a need to wake it up after it has been off for a while all indicate SDM failure is approaching. However the length of time is unknown and no one can predict failure. Personally I would consider switching to screw drive if you have any concerns that failure in the field is going to cause you a problem. If not then keep using it until you don't feel like putting up with waking it up each time or it fails.

[naomi.mavro]

This is a very sad news. I think I will send back the lens although I really like it, especially because we do not have a Authorized Pentax Repair Center here in Romania and I do not want to take any risk.

[UncleVanya]

This is a very sad news. I think I will send back the lens although I really like it, especially because we do not have a Authorized Pentax Repair Center here in Romania and I do not want to take any risk.

Converting it yourself to screw drive is fairly easy but unless you got it at a good discount it does not make sense for you to convert it.

[naomi.mavro]

Because the ebay seller was so kind to send me a refund I decided to send the lens to the repair center in Germany. Waiting for the repair estimation, apparently is a software problem but is not for sure. Next week I will receive the infos. Regards everyone.