Will phase focusing go the way of the dinosaur?
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From: Ray Fischer on 7 Jun 2010 02:30 James Nagler <jnagler(a)spamproofed.net> wrote: > rfischer(a)sonic.net (Ray Fischer) wrote: >>RichA <rander3127(a)gmail.com> wrote: >>>Forget for the moment the benefits of going away from phase focusing, >>>such as much lower cost going to contrast focusing. Phase's main >>>important claim to fame is speed. But that is diminishing, or >>>contrast is improving. The main problem with phase focusing is the >>>constant problems with back or front focusing with various lenses, >>>doesn't matter what brand of camera. This is a pain, one that >>>contrast focusing apparently does not have or if it does, the >>>incidence is very small. Most decent DSLR's now come with >>>compensation features for this, but who wants to have to go though the >>>elimination process for each lens they own and how often has this >>>compensation not even been enough, or consistent? >> >>And how many contrast-detection focusing systems can track moving >>objects at 10 frames per second? > >If I need 10 frames per second then I put my camera in 30 or 60 frames per >second video mode. Contrast focusing seems to track moving subjects just >fine in video mode. And after all, focusing doesn't have to be as accurate with a 2MP camera. By the way, we've all seen how fast video cameras are at adusting to sudden changes in focus. Not very. -- Ray Fischer rfischer(a)sonic.net
From: Ray Fischer on 7 Jun 2010 02:30 Rich <rander3127(a)gmail.com> wrote: >On Jun 6, 6:19�pm, rfisc...(a)sonic.net (Ray Fischer) wrote: >> RichA �<rander3...(a)gmail.com> wrote: >> >Forget for the moment the benefits of going away from phase focusing, >> >such as much lower cost going to contrast focusing. �Phase's main >> >important claim to fame is speed. �But that is diminishing, or >> >contrast is improving. �The main problem with phase focusing is the >> >constant problems with back or front focusing with various lenses, >> >doesn't matter what brand of camera. �This is a pain, one that >> >contrast focusing apparently does not have or if it does, the >> >incidence is very small. �Most decent DSLR's now come with >> >compensation features for this, but who wants to have to go though the >> >elimination process for each lens they own and how often has this >> >compensation not even been enough, or consistent? >> >> And how many contrast-detection focusing systems can track moving >> objects at 10 frames per second? > >None, yet. Wishful thinking doesn't count. -- Ray Fischer rfischer(a)sonic.net
From: David J Taylor on 7 Jun 2010 03:09 "RichA" <rander3127(a)gmail.com> wrote in message news:edf0060b-5c66-46b6-a6d7-73c66719150c(a)g19g2000yqc.googlegroups.com... > Forget for the moment the benefits of going away from phase focusing, > such as much lower cost going to contrast focusing. Phase's main > important claim to fame is speed. But that is diminishing, or > contrast is improving. The main problem with phase focusing is the > constant problems with back or front focusing with various lenses, > doesn't matter what brand of camera. This is a pain, one that > contrast focusing apparently does not have or if it does, the > incidence is very small. Most decent DSLR's now come with > compensation features for this, but who wants to have to go though the > elimination process for each lens they own and how often has this > compensation not even been enough, or consistent? You appear to forget that phase-focusing provides an instantaneous and continuous measurement not only of the direction of the focus error, but its magnitude as well, so that the camera knows which direction to move the lens, and by exactly how much to move it. One lens move. Focus done. Contrast focus, by comparison, takes time to evaluate how much in focus an image is, moves the lens in an arbitrary direction, evaluates the focus once again, has a 50% chance of finding the focus is worse so has to move the lens in the other direction, has to evaluate the focus again, move the lens, etc. etc., until the focus is worse again, so it's moved past the point of best focus, and finally has to move the lens back to /about/ the correct focus. "Will phase focusing go the way of the dinosaur?" No David
From: Bruce on 7 Jun 2010 03:19 On Sun, 06 Jun 2010 21:51:13 -0500, James Nagler <jnagler(a)spamproofed.net> wrote: >On Sun, 06 Jun 2010 22:27:01 +0100, Bruce <docnews2011(a)gmail.com> wrote: >>On Sun, 6 Jun 2010 13:04:27 -0700 (PDT), RichA <rander3127(a)gmail.com> >>wrote: >>> >>>Forget for the moment the benefits of going away from phase focusing, >>>such as much lower cost going to contrast focusing. Phase's main >>>important claim to fame is speed. But that is diminishing, or >>>contrast is improving. The main problem with phase focusing is the >>>constant problems with back or front focusing with various lenses, >>>doesn't matter what brand of camera. This is a pain, one that >>>contrast focusing apparently does not have or if it does, the >>>incidence is very small. Most decent DSLR's now come with >>>compensation features for this, but who wants to have to go though the >>>elimination process for each lens they own and how often has this >>>compensation not even been enough, or consistent? >> >> >>Only one brand has significant, systematic problems with AF accuracy >>and repeatability, and that is Canon. With all brands, there are of >>course the usual quality control issues, especially with tolerances >>that can cause problems. But only Canon has a system in which the >>problems are inherent in the design of the AF system. >> >>Canon has worked very hard to minimise these problems with firmware >>updates and more careful calibration of cameras and lenses. They >>haven't been eliminated, but they have been minimised to the extent >>that the vast majority of Canon users are not even aware of them. > >I disagree. Every last DSLR photo posted by every participant of these >newsgroups using all brands of DSLRs has shown focusing errors. More often >due to having too shallow DOF but still compounded with poor auto-focusing. You have a point, but these are down to operator error and, perhaps, some manufacturing tolerance problems which are there in all brands. The issue with Canon is different; the fundamental design of Canon's AF systems, especially those in the EOS 1D Mark III/IV, gives rise to systematic errors. These errors are such that they can only be partially compensated for in firmware and/or by recalibration of the camera body and/or lens.
From: Bruce on 7 Jun 2010 03:41
On Mon, 7 Jun 2010 08:09:12 +0100, "David J Taylor" <david-taylor(a)blueyonder.co.uk.invalid> wrote: > >You appear to forget that phase-focusing provides an instantaneous and >continuous measurement not only of the direction of the focus error, but >its magnitude as well, so that the camera knows which direction to move >the lens, and by exactly how much to move it. One lens move. Focus done. It also provides an estimate of the rate of change of sensor to subject distance, enabling predictive autofocus. That is not practicable with contrast detection AF, which means that cameras thus fitted are fundamentally less well suited to sports and wildlife photography, and also making images of children. I suspect that an active child is a more difficult subject to focus on than a bird or a racing car. ;-) |