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04-24-2014, 09:49 PM   #1
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Pentax K-X and DA 35mm F2.4 Autofocus Problem

I have just purchased the SMC DA 35mm F2.4 for use with my Pentax K-x. I have taken many test shots today of outdoor and indoor items and I have found that using the viewfinder autofocus (phase detection) is generally out of focus compared to using the liveview autofocus (contrast detection) particularly at F2.4 and values near that. Autofocus for phase detection is set to centre spot and I focus on the object. Autofocus for liveview is set to Face detect and I focus on the object. I am shooting in Aperture priority mode. As another test I have just taken shots of a soccer ball bar code outside from a distance of approximately 1.5 metres above the ball. ISO was fixed at 400. I took 2 shots using each mode at F2.4, F4, F8 and F11. What I noticed is that the viewfinder focus improves as the aperture gets smaller Eg. F8. I also note that the F2.4 shutter speed was 1/4000 s which is quite high. I have attached the 2 photos from F2.4 and the 2 photos from F8 and F8 the focus is good for both but the viewfinder focus for F2.4 is poor as expected. I have connected my Sigma F3.5-6.3 18-200mm lens and I it works well with both modes. Using liveview all the time may not be convenient depending on the environment I am in. Is my concern a problem with the lens or camera or something to do with how I am using it? I note that I cannot do individual lens focus correction on the Pentax K-x unlike some other models.
Thanks, AJ

Attached Images
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PENTAX K-x  Photo 
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PENTAX K-x  Photo 
04-25-2014, 05:10 AM   #3
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Thank you for the quick response. That information on using debug mode enabled me to fine tune my autofocus and resolve the autofocus problem.
04-26-2014, 01:34 AM   #4
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no problem!


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autofocus, camera, detection, f2.4, f8, focus, k-x, lens, liveview, pentax, pentax help, pentax k-x da 35mm f2.4, photography, viewfinder
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