05-12-2011, 09:39 PM
[quote name='Sylvain' timestamp='1305235828' post='8273']
Others will correct me if I'm wrong, but how I understand it, there's no such thing as sampling rate in phase detection AF. It's rather a "one time measurement" of phase difference then translated to a defined amount of focusing lens movement. So I'm not really sure what more could be done here to gain a remarkable of magnitude of improvement.
It seems to me that moving to "final image" based analysis (e.g. based on actual imaging sensor feed, contrast AF) would allow to put a lot more intelligence in scene detection (including tracking) as processing power keeps rising.
Greetings,
S.
[/quote]
Of course there is a sampling rate, the AF sensor samples all the time. Whether all those samples translate into AF movement commands is something different.
Besides that, PD AF is not a "one time measurement" affair, although that is a widespread belief on the interweb. PD AF still happens in different steps, even though the steps are not broken down into so many tiny ones like with CD AF.
You are correct in that a comparison of "sampling rate" makes no sense.
Tracking a subject moving from/to the camera will always be a problem with CD AF, as it does not see depth in any way. It can not tell if unsharpness is because a subject is in front or behind a subject.
Only integrating PD AF into the imaging sensor will give imaging sensor AF that capability. but then it again will be PD AF.
Others will correct me if I'm wrong, but how I understand it, there's no such thing as sampling rate in phase detection AF. It's rather a "one time measurement" of phase difference then translated to a defined amount of focusing lens movement. So I'm not really sure what more could be done here to gain a remarkable of magnitude of improvement.
It seems to me that moving to "final image" based analysis (e.g. based on actual imaging sensor feed, contrast AF) would allow to put a lot more intelligence in scene detection (including tracking) as processing power keeps rising.
Greetings,
S.
[/quote]
Of course there is a sampling rate, the AF sensor samples all the time. Whether all those samples translate into AF movement commands is something different.
Besides that, PD AF is not a "one time measurement" affair, although that is a widespread belief on the interweb. PD AF still happens in different steps, even though the steps are not broken down into so many tiny ones like with CD AF.
You are correct in that a comparison of "sampling rate" makes no sense.
Tracking a subject moving from/to the camera will always be a problem with CD AF, as it does not see depth in any way. It can not tell if unsharpness is because a subject is in front or behind a subject.
Only integrating PD AF into the imaging sensor will give imaging sensor AF that capability. but then it again will be PD AF.