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04-10-2015, 03:37 PM   #1
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Pentax Color/light Meter & PDAF

Maybe some of the experts can answer this question.


Would it be possible to replace the current 86K pixel color/light meter and PDAF sensors with a 1-2MP sensor with onboard PDAF? Using a 2MP sensor should give you much better metering and color and you could have 100+ PDAF points on the sensor. The sensor could provide most of the benefits of a mirrorless while retaining the OVF and using the main sensor for actual image capture. Features like face/eye recognition could be used and you would have more intelligent tracking in general. It would require a lot more processing power which would reduce battery life, but would the advantages out weight the negatives? Would it be possible? They would need the ability to project live information into the OVF for histogram or focus points.

04-10-2015, 04:24 PM   #2
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I'd eventually expect there to be diminishing returns (compared to the step up from 77 large segments to 86k pixels, for instance), and the increase in required processing power probably wouldn't be worth it for something that already works well. That's just my quick opinion. But IMO you're definitely thinking along the right lines for future tech development.

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04-10-2015, 06:51 PM   #3
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I'm no expert by any measure but I'll respond anyway.

This is an intriguing idea. It would eliminate the semi-transparent area of the main mirror and the small mirror behind it and their associated light losses.

I'm not sure how the PDAF would work, though. The PDAF pixels need to be precisely at the focal point, right where the focusing screen is located.

Unless you're thinking that the PDAF sensor would detect focus by "looking" at the image projected on the focusing screen? My guess would be that the scattering of light by the focusing screen would preclude accurate measure but I don't really know. Interesting concept nonetheless.
04-12-2015, 03:11 AM   #4
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PDAF compares light that gone two different paths- one from (say) left side of lens and other from right side (or upper and lower). If you put a focusing screen in light path, then it's not possible anymore (light from all lens sides hits focusing screen, refracts and mixes together, so any info that PDAF can use is lost). That's why AF sensors and metering sensors on every SLR are separated (metering sensor needs all the light from the lens to work properly, so it is placed after the FS)

Face recognition in OVF mode is implemented on K-3 even now (you can look in EXIF via exiftool, there is tag "Faces detected", it sometimes has value greater than zero even in EVF mode)

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