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Forum: Pentax DSLR Discussion
08-17-2009, 04:24 PM
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I can tell you without a doubt that AFc slows down fps on my camera under certain conditions. I haven't tested it yet to see how much. For the record (not an excuse) ai servo also seems to slow down my Canon. I'm not an engineer so I don't pretend to understand it but it seems to be common across platforms.
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Forum: Pentax DSLR Discussion
08-14-2009, 10:06 PM
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I have to disagree with the statement on lens speed. The DOF in your shot is huge and the closing rate on that car relative to you is not that great. Look at how far the lens has to move to go from Infinity to 5 meters on your lens (not very far). You don't need a fast lens or a fast camera to make that shot work - you just need a skilled photographer. People have always said that Pentax lenses were slow because of the example I showed with the K20 (any target approaching you at moderate speed will ALWAYS be OOF on k20 using AF.c if the DOF is narrow). I have always believed that the Pentax lenses were "fast enough" (I would not call them fast) but that the lack of predictive AF in the camera was the weak link in the system. My tests with the k-7 prove my point. The DOF in that shot is about 12 inches and it still came out razor sharp.
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Forum: Pentax DSLR Discussion
08-14-2009, 02:17 PM
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i'll be busy for the next few days so I won't have a chance to write it up properly with examples for a while but the Predictive AF definitely works on the K-7. I tested it against K20 with a bicycle coming down at hill at 20mph. I used both bodies and I used DA*200/2.8, FA*300/2.8, and DA*50-135/2.8. The results are not 100% perfect but the K20 had almost 0% in focus shots while the k-7 had anywhere from 50% - 100% in focus shots depending on the lens and the particular run. The fps takes a huge hit in this mode but it is sufficient - I need to double check but I think k20 and k7 had almost the same frame rate during these tests.
Although 20mph is not super fast, the closing rate (distance between rider and camera) on the tight crop shots I was taking is extremely fast. Remember camera focusing is not linear so tight crops focused all the way down to minimum focus distance is quite difficult. People shooting race cars and motorcycles do not stand directly in front of the vehicle so closing rates are usually significantly less and the DOF is usually greater.
edit
here's a quick and dirty look - all shots wide open (F2.8) at ISO 100
K20
K-7
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