Originally posted by Rupert These are interesting conversations on the AF systems, I wish I was more technically literate where I could follow them better. I know nothing of Canon, I don't think I have ever held one, but I have used a friends Nikon D700, and the focus is very fast and accurate as well. What is in their system that seems to make them so good at fast AF?
Before anyone gets all bent out of shape, I am just asking to see if there is a reasonable explanation. If you want ten good reasons why the K5 is better than the D700 (my opinion), I can certainly give them to you, there is much more to a great camera than just fast AF, but I am curious about their AF system, and you guys seem to know a lot more about AF than I do.
Regards!
Rupert,
I have been shooting Pentax for decades and have not so much experience with other brands, but I read what I can about the technology, so I have gleaned a few nuggets along the way.
From what I have seen working some Canon Raw files from fellow shooters at events (and many would argue that this is NOT true) Canon gives up a bit of accuracy for speed. Nothing major, mind you, but sometimes speed gets an acceptable shot where my Pentax body would still be thinking about it. This is not true of all models, as the 5D series has a rep of being slow.
I think that Canon has an advantage on the higher-end gear with the ring style ultra-sonic AF lenses. This technology is a powerful and fast (and more expensive) solution that Canon has had for many years and they have had time to perfect it. Nikon has similar technology. I seem to recall that Canon has at one time or another, had some higher failure rates on the micro-motor style focusing they use in the lower end lenses, but you do not hear too much about that these days.
At the lower level, I am not sure that Canon is much better than Pentax, at least since the K7.
I think that the best Nikon machine uses a whole lot more focus points than we have available, but is pretty smart about when to use them. Most of this is selectable by the user and does require getting the setup right for a given situation or you risk having the camera make choices that might be completely wrong in a given situation. You can read some of this sort of thing happening at the other forums.
Both Nikon and Canon seem to have better programs for AF tracking than anything Pentax has made to date. You can read about how they use AF points that are not even visibly selected to start tracking the motion of the image in the frame while handing off the focus duties to the sensors in the predicted path of the subject. The lens is also running in a continuous servo mode when doing this, which means it does not stop and think and re-adjust, it simply keeps moving the focusing motor in the predicted direction.
In short, at least for AF-C, the system is intelligent and much more sophisticated than that of Pentax, at least on the higher end bodies.
I mentioned the use of higher precision f2.8 sensors on some higher-end Canon bodies which work with the pro lenses. This makes for a more accurate focusing calculation.
It also seems that the processing horsepower is higher for both Canon and Nikon, but I have no proof of this other than the cameras are generally faster in almost all regards, especially at the higher-end or at least above the low end models.
Maybe Canon and Nikon spend a bit more money on the AF optics to prevent CA or other optical aberrations from influencing the AF acccuracy? After all, with the volumes they sell, they can make better parts and probably not pay as much as Pentax does for the cheaper ones.
It could be that the best algorithms and technologies have been patented. I know that Canon ring style ultrasonic AF was. This would leave others to find some way to work around the patents and still get equivalent performance, which is not an easy task.
As for better AF, well, it isn't always true for every model. Canon has been suffering with AF issues on the 7D, and the Nikon D7000 is also having quite a few AF issues. I recall big issues with a top of the line Canon sports machine that were never really addressed, and Nikon had some issues early on with the D70, which is where the original focust test charts started showing up. The canon 10D also had AF issues as I recall.
So, we are not alone, but, for the most part, you can send your badly focusing Nikon or Canon in and they seem to get them fixed. We have no evidence of that so far on any Kr or K5 as best I can tell.
Ray