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05-30-2010, 12:13 AM   #1
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Pentax Screwdrive AF vs SDM AF compared! (on DA* 50-135mm)

I decided to do a cunning test to find out which is faster: Pentax traditional screwdrive AF, or the new SDM AF motor.

SDM
[YT]http://www.youtube.com/watch?v=CjL1QNR9TmU[/YT]

Screwdrive
[YT]http://www.youtube.com/watch?v=8ZCw83BqFYw[/YT]

AF speed findings (EV 14, daylight) using the DA* 50-135mm:
AF Type Time to focus from infinity Time to focus from min
SDM 6/30s (0.2000s) 20/30s (0.6667s)
Screwdrive 4/30s (0.1333s) 18/30s (0.6000s)

Conclusion: Pentax SDM is unfortunately not faster than screwdrive AF, although it is much quieter.


I guess this simply says that Pentax should really work on either noticeably increasing SDM speed, to make it worthwhile for us, or simply continue using screwdrive AF with potentially quieter or more powerful motors.

Several tests were done for each category, and the most frequently-occurring result was selected to estimate the true speed. Results varied from 18-19/30s for the screwdrive measurement, and from 20-21/30s for the SDM measurement. Times were found by analyzing each video frame-by-frame.


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05-30-2010, 12:17 AM   #2
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nothing new Adam, this fact has been know ever since SDM came with first DA* lenses...
05-30-2010, 12:22 AM   #3
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This is consistent with my experince using different screwdrive/SDM lenses.
How did you manage to force the camera to use screwdrive instead of SDM with this lens?
05-30-2010, 12:27 AM   #4
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QuoteOriginally posted by PePe Quote
This is consistent with my experince using different screwdrive/SDM lenses.
How did you manage to force the camera to use screwdrive instead of SDM with this lens?
Ole's K10D still has firmware v1.1 on it, which doesn't support SDM


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05-30-2010, 12:48 AM   #5
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is it possible to use the K10D's firmware to downgrade the K20D, K-7, and kx firmwares?
05-30-2010, 12:52 AM   #6
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Nope. If you somehow managed to force it into one of your other cameras, they would become as useful as a brick.

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05-30-2010, 01:04 AM   #7
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Would be interesting to see if they behave the same at EV5 or lower.
05-30-2010, 01:30 AM   #8
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brick would be nice.

05-30-2010, 03:25 AM   #9
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We've known this indeed and to me it's the SDM fine focusing phase that lags behind the screwdrive lens mechanism. Quiet is not enough IMO, and the current SDM failures along with their slower AF speeds are quite an indictment on Pentax's premier lens lineup.

I'm holding out on Pentax's SDM development coming through soon...
05-30-2010, 03:54 AM   #10
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QuoteOriginally posted by Ash Quote
I'm holding out on Pentax's SDM development coming through soon...
x2!

i'd love to buy the 16-50 and 50-135 but not with all the current complaints...
05-30-2010, 04:07 AM   #11
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While this may not matter much... it should be noted that it's not specific to Pentax only.
Sony's SSM (SDM equivalent) is also slower than screw-drive, at least with some lenses. Back in the Minolta days, SSM was indeed faster, but Sony DSLRs have improved screw-drive motors (A700 for example is about 1.7x faster than A100, which uses the Minolta implementation).
05-30-2010, 07:37 AM   #12
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I would have liked to hear the focus mechanisms instead of music.
05-30-2010, 07:54 AM   #13
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I believe quieter AF is much more important then split second faster focusing specially if you are shooting in places where noise can disturb unless nano seconds are really important to you.
05-30-2010, 08:17 AM   #14
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What happens if you put a tape over SDM power pins?
05-30-2010, 08:24 AM   #15
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QuoteOriginally posted by ytterbium Quote
What happens if you put a tape over SDM power pins?
Nothing, I believe
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