On-sensor PDAF, will it be as good as mirrored cameras?

Started Oct 10, 2013 | Discussions thread
Bruce Oudekerk
Bruce Oudekerk Veteran Member • Posts: 3,463
Re: On-sensor PDAF, will it be as good as mirrored cameras?

jackgreen wrote:

Interestingly this massive thread is mostly off-topic.

The question here is much more complex, I think, than 'just' the issue of PD on-sensor.

Fundamentally PDAF works differently than CDAF and the lenses themselves are different. Presumably this is why Alpha mount lenses on NEX cameras focus MUCH MORE slowly under contrast detect than a native E-mount lens. Conversely I'm wondering if the E-mount lenses CAN focus any faster using any form of PD or if they are limited by their optimization for CD. The PDAF on-chip specific question for e-mount lenses should be answered fairly soon with the new cameras. So the real question might be PDAF on-sensor with what lenses? We can look to Olympus for some hints. The 4/3 lenses that were optimized for PD were relatively slow on CD micro 4/3 cameras but now the latest M1 has made significant headway with on-chip PD. Its not there yet but getting closer. And as stated elsewhere we can look to Canon 70D where PD gets focusing essentially there with a final CD check. Slower but perhaps more accurate in some situations....or not. So it might be better for many and not so good for some photographers.

The next issue that I believe the topic assumes is that mirrored cameras are the end...to end all... in focusing. Quite frankly focusing in general is sloppy on almost all mirrored cameras (OK... all cameras) unless you are using a single point and even then the hit rate is not guaranteed to be 100%. If anything, good CD is more accurate than good PD. The catch there is speed and that has been a trade off for quite a while regardless of PD or CD. When I bought my a850 there were studies that indicated that is had very accurate center point focus...more so than much of the competition... but it was slower. I have found this to be true. And that's judging PD to PD. When judging CD to PD (off topic) or on-sensor to off-sensor PD (on topic), the 'Will it be as good' question becomes fuzzy and qualifications immediately branch the issue out into other areas. No wonder the answers are off topic. Although admittedly my comments have been more off topic (ish) than most:)

The last issue is operator error and how that interacts with the strategies that different cameras employ during the focusing process. These strategies vary according to a variety of other fundamental camera parameters. For example, when the camera has faster focus lock it can afford to perform more complex tasks, which in my experience often tend to lower the hit rate in certain situations. These qualifications will invariably be a consideration when judging CD to PD on-chip and in judging PD on-chip to PD off-chip.(ie mirrored cameras)

With that said, we are ALL waiting on information that will give us a frame of reference to this question and the inevitable compromises that will manifest themselves.


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