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09-23-2015, 10:47 AM   #1
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300mm f4 SDM problem

I have a DA* 300mm f4 that I use almost exclusively for wildlife and bird photography, so I don't use it on a daily basis. It was bought new about 20 months ago. I like it and have had no problems with it until recently. In June, I bought a new k-3, intending to replace my trusty k-5. In August, we took an extended trip with a few wildlife photo ops, so I took the k-3 and the 300mm. I had tested the k-3 with all of my lenses briefly before leaving to be sure everything worked. While attempting to photograph some whales from a boat, the 300mm suddenly ceased to autofocus. Nothing I tried would revive it. For the rest of the trip it was manual focus only. When I returned, I tried the 300mm one more time and still no joy. I was planning on getting it repaired or attempting to convert it to screw drive. Today, I had the idea of trying it on the k-5 (which I haven't had time to sell yet). Autofocus worked right from the beginning. I then put it back on the k-3, and it is working again on the k-3. When my lenses are not in the camera bag for travel, they are either on the camera or residing in a translucent fairly tight box with a silica gel tin. I have no other SDM lenses (nor will I after this one), and have never had a problem with any of them. Thoughts? I'm not going to send it for repair at this point, but I'm wondering if I should attempt the screw drive conversion while I still have the k-5, which seems to be required for that operation. Are there any repair shops that will do the screw drive conversion with some warranty or guarantee that they won't brick the lens?

09-23-2015, 10:59 AM   #2
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Have heard of very few SDM problems with the 300. With the other lenses that seem to be more prone to them, some have had success "waking it up" just by turning the ring back and forth. Search for threads on that...
09-23-2015, 11:59 AM   #3
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I tried that several times while on our trip with no success. I tried it again a few weeks ago when we arrived home without success, then I put the lens in storage. Today, as soon as I took it out of storage and mounted it on the k-5, it worked fine. I know that timing and causation are not the same, but it does seem weird.
09-23-2015, 12:03 PM   #4
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Was it perchance humid in the area where it failed?

09-23-2015, 12:37 PM   #5
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Not particularly. We were off the coast of Labrador. It was probably about 40 deg.F, partly sunny, a bit windy. No rain. We had been viewing a moderately sized iceberg and then switched to the whales. I changed lenses carefully in the cabin. The lens focused once or twice and then quit. The autofocus continued to fail for the balance of the trip (2 weeks or so). When we returned to shore, I tried cleaning lens and camera contacts, as well as working the focus ring back and forth, but all to no avail. I also use an 18-200 Sigma with in lens focusing, as well as a 10-20 Sigma and the 35mm f2.4, both with screw type focusing. The only one with a problem was the 30mm.
09-23-2015, 04:18 PM   #6
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QuoteOriginally posted by mechmike10 Quote
Not particularly. We were off the coast of Labrador. It was probably about 40 deg.F, partly sunny, a bit windy. No rain. We had been viewing a moderately sized iceberg and then switched to the whales. I changed lenses carefully in the cabin. The lens focused once or twice and then quit. The autofocus continued to fail for the balance of the trip (2 weeks or so). When we returned to shore, I tried cleaning lens and camera contacts, as well as working the focus ring back and forth, but all to no avail. I also use an 18-200 Sigma with in lens focusing, as well as a 10-20 Sigma and the 35mm f2.4, both with screw type focusing. The only one with a problem was the 30mm.
I have one idea what could have happened. This is just a working hypothesis. Did you rapidly change the temperature of the lens, for example went out of the cabin, right into a cold environment?
This could have changed the diameter of the SDM friction surface or the size of the stator (see fig. 1). Those two have to be very well matched, so perhaps something fell out of alignment and once the temperature of the lens equilibrated, it stopped being the problem. This could be exacerbated by a worn out piezo drive friction ring. If the SDM is working inconsistently, that could be another sign of it being worn out and then it might be worthy to convert it to a screw drive. Just some thoughts, not a diagnosis, but maybe it's a direction to think of.

Fig. 1 https://en.wikipedia.org/wiki/Ultrasonic_motor#/media/File:Piezomotor_type_inchworm.gif

Last edited by rrstuff; 09-23-2015 at 04:22 PM. Reason: clarity
09-23-2015, 05:39 PM   #7
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That is an interesting thought, but it wasn't that much warmer in the cabin than outside. Also, it certainly had plenty of time to equalize in our hotel room overnight and during subsequent days in the car and rooms overnight. Up to this incident, it had worked consistently and well, and it seems to be working well again. I am at a loss.
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