02-02-2013, 04:51 PM
[quote name='joachim' timestamp='1359793754' post='21705']
Hi
Having phase detect AF on mirrorless cameras seems to be gathering traction, apart from µFT. Since I am mostly interested in µFT it sort of bypassed me so far.
Anyone got an idea how that works? I understand some pixels are devoted to AF work. Are these still used for the image also? Or are there holes in the image which need to be interpolated away? Similar interpolation to mapping out dead pixels?
Any good diagrams out there on how this works?
Thanks
Joachim
[/quote]
Yes, these are interesting questions that I posed elsewhere in a different context as well. What happens with these pixels, are they mapped out, or if not. Possibly half of the pixel still has information content? Simplistically, Canon's implementation, given the randomness of the distribution of the points on the sensor, suggests they are simply mapped out.
The reason the issue come up elsewhere was, why Canon didn't have/allow the high magnification zoom in during video that the previous model had. Well, the only difference is the sensor. If you zoom in now in video to "pixel" peeping levels, you may now suddenly notice your "bad" pixels, and you have may not enough processing power or speed during video to map it out.
The Nikon implementation has apparently rows of pixels for Phase detect on the sensor - more in line with phase detectors behind the mirror. Again, they must be mapped out somehow.
I'll try to find the web site that shows the sensors.
Maybe the reason the Canon implementation doesn't work well is the single random dots. That sounds like it's not going to give high resolution, just some approximation, which then is supplemented with contrast detect. This fits with how it's described as working.
Edit: found the teardown web site now.
http://www.chipworks.com/blog/recenttear...-t4i-dslr/
shows how the pixels look.
Hi
Having phase detect AF on mirrorless cameras seems to be gathering traction, apart from µFT. Since I am mostly interested in µFT it sort of bypassed me so far.
Anyone got an idea how that works? I understand some pixels are devoted to AF work. Are these still used for the image also? Or are there holes in the image which need to be interpolated away? Similar interpolation to mapping out dead pixels?
Any good diagrams out there on how this works?
Thanks
Joachim
[/quote]
Yes, these are interesting questions that I posed elsewhere in a different context as well. What happens with these pixels, are they mapped out, or if not. Possibly half of the pixel still has information content? Simplistically, Canon's implementation, given the randomness of the distribution of the points on the sensor, suggests they are simply mapped out.
The reason the issue come up elsewhere was, why Canon didn't have/allow the high magnification zoom in during video that the previous model had. Well, the only difference is the sensor. If you zoom in now in video to "pixel" peeping levels, you may now suddenly notice your "bad" pixels, and you have may not enough processing power or speed during video to map it out.
The Nikon implementation has apparently rows of pixels for Phase detect on the sensor - more in line with phase detectors behind the mirror. Again, they must be mapped out somehow.
I'll try to find the web site that shows the sensors.
Maybe the reason the Canon implementation doesn't work well is the single random dots. That sounds like it's not going to give high resolution, just some approximation, which then is supplemented with contrast detect. This fits with how it's described as working.
Edit: found the teardown web site now.
http://www.chipworks.com/blog/recenttear...-t4i-dslr/
shows how the pixels look.