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11-03-2012, 07:19 PM   #1
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If sdm fails

If the camera's sdm fails, would the screw style auto focus be just as fast?
I would like to eventually want to buy a used 50-135 2.8 but know the purchase will have risks.

Thanks

Randy

11-03-2012, 07:25 PM   #2
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I know this one. No, because if your camera supports an SDM lens, the screwdrive is disabled. Your K10D is a special case; you can get screwdrive to work if you roll back the firmware to a pre-SDM version. Older cameras are screwdrive-only, newer models are SDM-only with an SDM lens. Yes, it makes no sense.

Edit: I remember users at the time saying there was little or no speed difference between the two.
11-03-2012, 07:27 PM   #3
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The K10D with early firmware, K100D, K100DS, K110D, and ist camera bodies can drive the screwdrive. No other Pentax body will use the screwdrive on an SDM lens, even when the SDM is broken.
11-03-2012, 07:46 PM   #4
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QuoteOriginally posted by Aegon Quote
The K10D with early firmware, K100D, K100DS, K110D, and ist camera bodies can drive the screwdrive. No other Pentax body will use the screwdrive on an SDM lens, even when the SDM is broken.
Wouldn't a firmware change that allowed the user to choose be a big step forward, and easily managed?

11-03-2012, 08:43 PM   #5
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Firmware could easily allow SDM to be disabled. But that firmware doesn't exist for any model, yet. Its on my Ricoh wishlist, though.
11-03-2012, 09:01 PM   #6
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We've been through that discussion many times before and for a long time also. SDM is considered to be Pentax's higher level focusing mechanism, and being designed not to fail (yet we know that it does) there wouldn't be much technical benefit to add the screwdrive capability. Some SDM lenses (mostly newer ones) do not have an inbuilt screwdrive mechanism in the lens. I would presume Pentax is thinking hard about SDM reliability and refining their future top lens lineup bearing this in mind.
11-03-2012, 09:01 PM   #7
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A silly question...how does the camera identify that a certain lens is SDM? Is there a way to "fool" the camera into thinking that is a, let's say, FA 50-135 (which doesn't exist)?

I guess someone with a broken SDM could try to selectively block electrical contacts...but this solution sounds too easy to be true. Maybe somebody could invent a "chipped" un-SDM-izer. If Sigma has been able to reverse engineer the electrical contacts for their own SDM, in theory, an un-SDM-izer is feasible.
11-03-2012, 09:02 PM   #8
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That too has been tried. Doesn't work.

11-03-2012, 11:50 PM   #9
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get a k-01...

my own k-01 can use screwdrive to AF the 50-135 when one of the sdm pin is broken

https://www.pentaxforums.com/forums/pentax-k-01/191080-new-purpose-k-01-reviv...autofocus.html
11-03-2012, 11:51 PM   #10
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QuoteOriginally posted by HSV Quote
A silly question...how does the camera identify that a certain lens is SDM? Is there a way to "fool" the camera into thinking that is a, let's say, FA 50-135 (which doesn't exist)?

I guess someone with a broken SDM could try to selectively block electrical contacts...but this solution sounds too easy to be true. Maybe somebody could invent a "chipped" un-SDM-izer. If Sigma has been able to reverse engineer the electrical contacts for their own SDM, in theory, an un-SDM-izer is feasible.
there is 2 gold metal pieces on sdm lens..if you tried to block any of the 2 contacts..the sdm will not work and the cam will think that its a mf lens
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