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09-14-2014, 01:02 AM   #1
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K3, K5II spot af

I have a K3 and generally use spot af, the centre spot and recompose. Now the K3 has 3 af spot sensors for fast f2.8 lenses & K5II has has one.

So the questions begs itself if these af sensors are best for the faster lenses then are the other af sensors best for slower lenses or is there no difference.

Whats your views or experience?



09-14-2014, 02:45 AM   #2
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With fast lenses, the 3 center ones should be more accurate in theory. With slower lenses there's no benefit but also no drawbacks to using the center points.

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09-14-2014, 09:29 AM   #3
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QuoteOriginally posted by screwdriver222 Quote
So the questions begs itself if these af sensors are best for the faster lenses then are the other af sensors best for slower lenses or is there no difference.
If Pentax followed the convention of other makers (e.g. Canon), the f/2.8 sensors should be dual with f/5.6 meaning that there is no black-out* with slower lenses. The remaining f/5.6 sensors work equally well with both slower and faster glass, though they will become inoperative if the mounted lens is slow enough. I have no idea when that point would be reached, though I think it is a good guess that there are precious few f/8 AF lenses out there.


* The PDAF system operates on a principle similar to a traditional split-image rangefinder found on many film SLRs and on aftermarket focus screens such as the KatzEye. At narrow apertures the prism refracts the light outside the sensor aperture resulting in no light to the sensor or "black out".

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