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03-21-2011, 11:21 AM   #1
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Screw driven AF cameras. More high end = better screw drive?

or is the screw drive the same generally?

eg, does the K5 have a better screw drive then the K10D?

03-21-2011, 12:23 PM   #2
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I have both these cameras and the torque is about the same. The K10D was about the same price at its introduction as the K-5 was. Same high end level.
But K-5 is much smarter and does not hesitate before turning the screw. Also it does not hesitate that much after turning the screw. So in practice the K-5 is much more successful in acquiring the focus really quick, good to track fast movement as for example flying birds. There the K10D struggled.
03-21-2011, 02:23 PM   #3
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It's not so much the screw drive itself that changed much, it's the software behind it that's drastically improved with each generation.
03-21-2011, 11:06 PM   #4
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I see...so theoretically speaking, if we could implant the algorithm into the K10D..the screw drive should be as quick. Providing of course Pentax did not put in place safeguards to prevent exactly that.

03-21-2011, 11:19 PM   #5
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If all the computer things were the same, theoretically, I think so. However, I know they've upgraded all the processing things, so it is most likely that the K10D lacks certain components to run AF calculations and such.

As far as the actual screw drive motor goes, I imagine the Pentax engineers would have selected a slightly "better" motor for the new cameras. I put better in quotes because I don't think it is a vastly better motor, likely just more durable to deal with a faster AF system.

Hope this helps,
03-22-2011, 07:12 AM   #6
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I think they're physically much the same... as far as testing goes for me, the K-5 I tried a the store turned the screw earlier by a fraction than the K-m. Used the same lens model for it... if there's improvement I guess it's not so significant... anyway the high-end lenses have their own focus motors XD
08-16-2011, 05:46 PM   #7
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There is a limit to how fast the screw can turn before it starts shredding the gears in the lenses. This may not seem like a big deal, but you need to factor in backwards compatibility, including such lenses as the poorly built FAJ line.
08-16-2011, 11:42 PM   #8
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Well, I went through the whole K10-K20-K7-K5 line, and each time I was able to compare two successive models with identical lenses before parting with the older one.

And the motor was indeed successively slightly boosted on each model. the K5 is a little tad faster than the K7, which is slightly faster than the K20, which is faster than the K10. The K-x (got this one for my wife) was somewhere between K20 and K7...

But other changes sometimes negate this advantage. For instance, the K5, although spinning its screw faster than the K7, actually starts moving the lens with a slight delay compared to it, and it's then pretty much a draw with lenses using a small focus throw (like the 18-55).
But it depends on what lens is used, and I guess with a macro lens with a huge focus throw, or say a Tamron 70-200/2.8 (with a lot of glass to move around), the K5 will have a more pronounced advantage.

08-21-2011, 10:29 AM   #9
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QuoteOriginally posted by Reportage Quote
I see...so theoretically speaking, if we could implant the algorithm into the K10D..the screw drive should be as quick. Providing of course Pentax did not put in place safeguards to prevent exactly that.
I doubt that Pentax boobie trapped the firmware. The firmware is proprietary and has never been released for external development, so if it were possible, you'd need to hack the firmware of both the K-5 and K10D.

You'd also need to account for differences in chipsets between the models.

Unless you like to tinker for the sake of tinkering, there isn't much point in bothering.
08-26-2011, 09:53 PM   #10
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As others have stated I think the mechanics have generally stayed the same but the software has improved making the AF in the K5 much better than the rest. The K5 doesn't necessarily go from minimum focus to infinity faster than the K10 but I doesn't "hunt" as much (go past the focus point then have to go backwards) so it will lock onto the subject much faster from initial focus.
09-01-2011, 01:19 AM   #11
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As I said above, motor speed was in fact improved successively ON ALL MODELS since the K10...

I always made comparisons while going from one model to its successor (K10->K20->K7->K5), using identical lenses on both bodies, and each time the focus ring was driven a little bit faster...

But that does not mean focusing time is better, as for instance the K5 starts focusing slightly later compared to the K7...
09-01-2011, 06:45 AM   #12
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I believe the motor in my K-x has lower torque than the one in my K20D.
09-01-2011, 07:30 AM   #13
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If you're using rechargeable batteries in it, that might explain it. After all, there's quite a difference between 6v and 4.8v.
09-01-2011, 08:38 AM   #14
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QuoteOriginally posted by Adam Quote
If you're using rechargeable batteries in it, that might explain it. After all, there's quite a difference between 6v and 4.8v.
Power determines torque, not voltage. Power = EI or current x voltage. I don't know how much current an Eneloop develops compared to a 1.5V alkaline, so I can't say which develops more power. Does anyone know?

The Li-ion battery in the K20D is 7.2V, so it could be more powerful than an Nimh rechargeable in the K-x.
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