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01-26-2012, 05:28 PM   #1
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3 lens story on K-5

I ordered a K-5 with Tamron 17-50 f2.8. It had a front focus issue (needed -5 correction) and occasionally when using f2.8 @ 17mm images were not focused. Returned and got the DA 16 - 45 that was doing well for the most part until I noticed the AF is not consistent (Also needed back focus +7 correction). Now I got the DA 17-70, ran same tests as the previous 2 and focus is spot on and no fine correction is needed.

This makes me wonder whether SDM has better focus performance than lead screw focus.

01-26-2012, 05:33 PM   #2
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SDM is more precise than screw drive. That's right.
01-26-2012, 05:47 PM   #3
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I too have found that SDM AF is more accurute than the normal screwdriven AF.
01-27-2012, 03:44 AM   #4
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QuoteOriginally posted by RGold Quote
I ordered a K-5 with Tamron 17-50 f2.8. It had a front focus issue (needed -5 correction) and occasionally when using f2.8 @ 17mm images were not focused. Returned and got the DA 16 - 45 that was doing well for the most part until I noticed the AF is not consistent (Also needed back focus +7 correction). Now I got the DA 17-70, ran same tests as the previous 2 and focus is spot on and no fine correction is needed.

This makes me wonder whether SDM has better focus performance than lead screw focus.
LensAlign could become a Pentax/Ricoh company...

Not many lenses have been desigend with both SDM or regular AF at different times - how can you compar?. Focus adjustment typically means that the camera is off. How can anyone judge on SDM performance - the same AF phase detection system is used inside the camera. You may stop SDM lenses faster and more accurately in the best position to get better results, but we can not really compare. Maybe we can assume that Pentax takes better care when designing more expensive SDM lenses...

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