17-70 sdm a bit lazy

[mggm59]

I bought on Ebay this lens for a good price as defective, expecting a dead sdm focus motor, but to my surprise the motor works

somehow but it seems to be sort of lazy or weak, i.e. If it is close to the focus point it more often than not reaches it, but if it is only a

millimeter away from it it makes a couple of noises as if it tried to move the ring and the gives up. Is this the normal behaviour of a

diying motor or is there something I can try to improve the situation?

 

Also, I started testing it, at 70mm it is frankly quite poor even at f8 (I bought it even if malfunctioning exactly to compare it to my 28-70

in my quest for a good replacement) and the focus ring is really ridicolous and irritating

[dshombert]

<p>Maurizio -- I've had three SDM lenses fail, and those are the exact symptoms they had in the early stages of failure. They were the 16-50, the 50-135, and the 200/2.8. I also had the 17-70 but sold it while the SDM was still working fine. Geez, I hope yours isn't it! I like the 200 so much that I insured it, so its repair was covered, and I'll maintain the insurance in case it happens again. Likewise, I've since bought the 300/4 and insured it, and no problems so far. But other than these two, I've given up on SDM lenses. I guess we'll never know exactly what the failure rate is of these lenses, but I'm convinced it's way higher than it should be. Yeah, the evidence is all anecdotal and not necessarily statistically significant. But anecdotal evidence PLUS the fact that three out of five of mine have failed is enough to convince me. Something's just plain wrong with the design or the components.</p>

[r.t. dowling]

<p>There might be more wrong with your lens than just the SDM motor. According to the resolution tests at PhotoZone, the 17-70 at 70 f/8 is nearly as good as the DA* 16-50 at 50 f/8, and at 40 f/8 the 17-70 is sharper than the 16-50. And, mind you, PhotoZone had a 17-70 that was slightly de-centered at 70. Maybe yours is badly decentered at 70.</p>

<p> </p>

[mggm59]

<p>From bad to worse then.... I will test it in the first sunny day I have some time, my tests were indoors on a test pattern.</p>

<p>I found an article on the web about fixing the SDM by opening the rear of the lens and wiggling around the motor, anybody tried this? Other solutions (given that it seems to be trying to move teh mechanism without being strong enough, I wonder if putting some silicon somewhere might help since instead of being the motor too weak, it might be some internal resistance which is too large..</p>

[ugur_akdag]

<p>Hi,<br>

I did what you mention on your post Maurizio.<br>

My lens bought from USA (new). After almost one year of seldom use I noticed one day that the SDM is weakened. It was not focusing in normal way and barely focusing in live view mode. I spray small amount of contact cleaner just below the focus ring. I seems work at least a while. But unfortunately the problem resurfaced again. So I opened the rear end out of curiosity and after removing the end cap I found that the small contacts are ready to spread around with a careless touch. I closed the cap back and continue using as it is (mostly in manual focusing mode).<br>

As of today, I decided to open the lens because it was eventually weakened and stop the focusing even in the live mode. <br>

Rear metallic cap carefully removed, under the cap, there were four screws that holding the plastic housing. I remove those too and after that I saw SDM motor & gears. Actually I was not expected such a small motor, I am surprised. I moved the gears a little bit to see if there is any mechanical interference I can feel. Mechanism seems to working smooth. I noticed the eight small plastic tubes located evenly around the barrel. I guess those were used for maintain the zoom friction. Two of them were out of their dedicated places. Due to the contact spray I assume, the length of the three tubes are little bit elongated (chemical reaction). I cut them to fit their places and blow the dust & assembled everything.<br>

Now it is working better. Its focusing in normal way (seem even more silently).</p>

<p>I hope it helps.</p>

<p>Regards,<br>

Ugur Akdag.</p><div></div>