G3 heralds the end of APS-C DSLRs

Started May 13, 2011 | Discussions thread
Lee Jay Forum Pro • Posts: 52,680
Re: and that's before we talk AF micro-adjust! ;-)

Anders W wrote:

ljfinger wrote:

No, it's the ability to move the lens' focusing elements and stop them. In low-light, it's the light available.


Evidence abounds. Plenty even in these forums from experts. CDAF works by guessing, moving, stopping and then determining whether or not the guess was right, and then either moving some more in the same direction if the guess was right or in the reverse direction if the guess was wrong.

Already we're getting to 120 frames per second. As technology improves and that readout speed keeps increasing along with faster processor speeds, CDAF will get better and better.

Still waiting for it to get better. It hasn't gotten much better in the last 10 years or so.

Single-area AF-S:
G2: 0.423 second
GH2 (2010): 0.273 second.

These numbers are meaningless. First of all they are largely dependent on the distance they had to go and the speed of the focusing motor. Second, they are for static subjects for which focusing speed is irrelevant. Third, most compacts can achieve similar numbers. They're all dirt-slow.

Focusing speed is important for tracking moving subjects, not for achieving initial focus.

PDAF is a very mature technology with some well-documented issues.

Most of which are imagined or largely overcome. I've owned 7 SLRs and about 30 lenses. I've had exactly one problem with one combination of lens/body, and that was corrected as a defect under warranty

That's just your subjective impression. Massive amounts of publicly available data tell a completely different story.

Reports on the forums are not a good overall cross section. The fact that these cameras have sold in the tens of millions over the years indicates that they are staying sold, which they wouldn't if they didn't work. So they do work.

CDAF eliminates those issues while introducing ones of its own. The difference is that the main issue with PDAF (keeping all elements of the imaging path in perfect alignment to ensure accuracy)

That's not the issue with PDAF. The issue is constant and known path length for the two separate optical paths (main sensor/AF sensors).

AF accuracy is certainly an issue with PDAF. This is partly due to the multiple path, partly to other factors.

Fortunately, it's not a big issue, and they miss far less frequently than CDAF cameras do when faced with challenging conditions. Yes, CDAF is more accurate theoretically in simple static conditions. For those that shoot in those conditions a lot, it should be satisfactory.

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Lee Jay
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