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07-18-2010, 02:01 PM   #16
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That's an interesting question about Nikon. They must have considered the sealing issue.

I think the 50-135 design with the solid shell and internal focusing is a brilliant way of sealing. The 16-50 design seems much more problematic with the sleeves. If the zoom expands in volume as it goes telescopic, than additional air must get into to fill the increased volume. That air can bring in humidity.

Perhaps its the law of unintended consequences that made Nikon forego sealing. If you have humid air inside the lens body, and cool the lens body sufficiently, one will get condensation on various parts inside the lens, perhaps the motor. It would be interesting to see if there is any correlation between different climates and SDM failure, and between seasons. Nikon may have thought it was better to let a lens breathe.
What mystifies me is why some folks have had 2 or 3 failures and others have had none - could that be climate related?

I don't believe in the burnout theory, most owners have reported an increasing difficulty with the lens focusing and then a failure. Sounds more like an undersized motor and a gradual build up of friction for some reason.

In any case, the good news is that Pentax built SDM into their lastest camera, the 645D and the lens for that. I don't believe that any company would release an expensive camera like the 645 unless they were confident that the SDM issue had been solved.

07-18-2010, 02:09 PM   #17
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QuoteOriginally posted by philbaum Quote
In any case, the good news is that Pentax built SDM into their lastest camera, the 645D and the lens for that. I don't believe that any company would release an expensive camera like the 645 unless they were confident that the SDM issue had been solved.
You are a lot more optimistic than I am. Historical examples to the contrary are quite abundant. (I am not singling out Pentax here.)
07-19-2010, 03:45 PM   #18
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This theory makes no sense IMHO.

If the seals make the lens havier to turn, put a bigger motor in!

So it may be an incorrect motor choice but not inherent to weatherproofed lenses.
07-19-2010, 04:02 PM   #19
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Manually turning the screw drive on the back of my 50-135 doesn't seem to take any more effort than doing on my other screw-drive lenses.

I doubt the SDM motor sees much, if any more resistance due to the weather sealing.

07-19-2010, 04:13 PM   #20
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QuoteOriginally posted by Peter Zack Quote
I wasn't forgetting Canon, just not sure of the facts and also they use a different motor system correct? Ring motors that are even stronger. But as posted above, maybe the Pentax motors were a compromise over size/strength and that's a large isse.
how about olympus ? their top grade zooms are all WR and no issues
07-19-2010, 04:38 PM   #21
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Peter. I also think it's a good theory. But I'd add to it. I think the small SDM motors may receive additional stress from one of my all-time favorite features of DA lenses, quick-shift. In the time it takes for the focusing gears to disengage as one turns the focus ring there has to be some amount of friction and stress involved.

As a former owner of the DA 17-70 in a very dry climate, I don't think moisture had anything to do with the SDM failing within the first few months of owning the lens. I think the bottom line was a hasty implementation to play "catch-up" and the usage of inferior parts, or too small of a motor, with little or no testing in their hurry to release the product.
07-19-2010, 05:42 PM   #22
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QuoteOriginally posted by PentaxPoke Quote
(Unfortunately no "Pentax Answer" shot is available. The photographer's lens was in for repair.)
Well, in this guy's defense, they were sitting next to a mud bog in an obstacle course. That explains the bag and Quantaray UV filter. Too bad they overexposed the shots by at least 2 stops (I saw the posts online) because they shot in M (I'm assuming) as the runners went through bubbly white foam that worked like a huge reflector.
07-19-2010, 05:49 PM   #23
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has anyone looked at the motor used today relitive to the motor used in th e power zooms?

I often wondered if pentax's experinece was based on these motors.

Although the power zoom moved a lot of masss, it was no where as frequent or fast as the auto focus requirements,

also, out of curiosity,. has anyone liiked at SDM failures and different users i.e. AF-S vs AF-C.

AF-c with the continual updating of focus can be really hard on a motor.

07-24-2010, 06:25 AM   #24
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QuoteOriginally posted by Peter Zack Quote
Rondec, that may be true. but it doesn't explain the slow focusing. I have a K20D that has the SDM disabled in the body. The motor in the body works as it should. So my DA*16-50mm on that body works as a screw drive lens. If I put it on the other 3 SDM cameras I have, the focus is fine in daylight but slow indoors or tougher lighting. On the K20D in screwdrive only it's just the same, Slow in low light and you need to do little tricks to get it to lock on.
Whoa....you were able to DISable SDM on your K20D and force it to use the screw drive on SDM lenses? How did you accomplish that (firmware hack, what?).

I know this is comparing apples-to-coconuts, but both of my screw drive lenses (DA 12-24mm f/4 and DA Limited 70mm f/2.4) always blew away the focusing speed of my DA* 50-135mm.....especially now that the DA*'s SDM is DOA!

What I wouldn't give to disable SDM on both my K10 and K20D.

Must...search...for...firmware...hacks....<cough>

Terry
07-24-2010, 07:21 AM   #25
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Somehow the SDM was shorted out in the camera, so it doesn't work at all.
07-24-2010, 07:45 AM   #26
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I have Taks that are over 30 years old and through the years have been exposed to some awful weather but I have never had water get inside one. I can understand the need to weather seal all the buttons and dials on a digital camera body. There are a lot of places on a camera body where water or dust could get in. I know that a MF and an AF lens are different animals but I haven't had an issue with any unsealed AF lenses either. If the weather is bad enough to be getting water on the front of the lens, I'm not going to be shooting anyhow. The August issue of Shutterbug has a few articles on protecting your gear and while water is mentioned, the issue of dust is the bigger problem. The author has spent time shooting in deserts and has had lenses damaged in that environment. As for water, he mentioned humidity and condensation in tropical climates as the big problem and improper storage that could cause mold and fungus issues. I have never even seen a desert so I can't claim any experience. The most sand I have seen is the beach.
07-24-2010, 07:30 PM   #27
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QuoteOriginally posted by tlwyse Quote
Whoa....you were able to DISable SDM on your K20D and force it to use the screw drive on SDM lenses? How did you accomplish that (firmware hack, what?).

I know this is comparing apples-to-coconuts, but both of my screw drive lenses (DA 12-24mm f/4 and DA Limited 70mm f/2.4) always blew away the focusing speed of my DA* 50-135mm.....especially now that the DA*'s SDM is DOA!

What I wouldn't give to disable SDM on both my K10 and K20D.

Must...search...for...firmware...hacks....<cough>

Terry
You can disable the SDM on your K10 by reverting to firmware 1.2. Unfortunately, I don't believe you can do it on the K20. If I remember his posts, it was a side effect of breaking something in the camera rather than a deliberate act.
07-24-2010, 10:27 PM   #28
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QuoteOriginally posted by Jodokast96 Quote
Somehow the SDM was shorted out in the camera, so it doesn't work at all.
Lucky you!



Regards,
Terry
07-25-2010, 03:06 AM   #29
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In the camera which has SDM now disabled, it was purely an accident. I was in a dark reception hall and changed lenses. I misaligned the lens to the camera mount and twisted the lens in a bit crooked. Something had to have shorted out and that body now is only screwdrive (K20D) I can't replicate the mistake to tell you how to do it safely. But 20 minutes before this, SDM was working normally. Immediately after putting the lens on correctly, it was SD only and has been for 6-7 months.

It's no faster but there's no strain on the motor with this combo.

I'd agree with the post above about the need for WS. It's nice peice of mind but I've used the DA16-45mm in driving rain more than once. Never any issues with that lens. A damp basement or storage area will do much more to kill a lens. The trick is not to zoom the lens in and out quickly driving the water inside the lens barrel.

It's not a WS issue IMO but a weak motor issue.
07-25-2010, 04:35 AM   #30
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Peter, that sounds like it to me too.
I was relatively pleased with the 16-50 copy I had (which I recently traded for an FA 43). I shared before how I had trouble locking focus at infinity at times, but that wasn't the only issue.

I found invariably that if I hadn't used the 16-50 for over a couple of weeks or so, I would have to 'attempt' focus a number of times before the SDM would engage and turn the focus ring. The longest I left the lens was a month, and it took me about 5 goes at holding the AF button down with the camera giving up, causing the flashing hexagon in the viewfinder, until the sixth go when the SDM motor finally kicked in. I was afraid then that if I left it for a couple more months it would never have started up again.

So the SDM to me is like a car engine - there comes a point when the car battery simply doesn't have the charge to turn the crankshaft over. Only with the SDM it's the other way around - charge is the same, SDM needs more to crank it....
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