amfoto1 wrote in post #16304026
Zone Focus <snip> works best when there are a lot of distracting objects behind or around or in front of your subject.
I'm sure he just means the opposite.
amfoto1 wrote in post #1630402670D doesn't have the 7D's Spot Focus (smaller AF point for higher precision, but a little slower focusing) or Expansion Points (similar to Zone Focus).
Spot AF isn't slower in executing than single point, provided you give it a contrast to work with. But since it looks at a smaller area, the probability that you, the photographer, doesn't aim it at something the camera can measure, is higher. Thus it may appear to be slower, but that is in finding anything at all, not in actually executing AF.
There's a significant difference between single point with expansion and Zone AF. At least as long as we are talking about Servo AF here, and I presume that is the most interesting thing, since One Shot AF is either successful or fails, and in each case it's often quicker than the photographer anyway.
Anyway, while using Servo AF, single point with expansion is equivalent to using all 19 points. In both cases you select a starting point, and the camera allows for the ability to hand over the tracking to one or more assisting points, if necessary. The only difference is how many such assisting points you enable, and thus how large an area they cover.
But Zone AF when using Servo AF behaves initially the same as it does in One Shot AF (which is the same way as all 19 points also behave in One Shot AF), in that it's the camera which decides upon which AF point within the zone to start with. Once it has done that, and that's done according to the standard principle, i.e. find something with good contrast, and if there are several points with good contrast, then pick the closest one. Once that's established, it will track with that point and hand over to other points in the zone if necessary.
amfoto1 wrote in post #16304026Orientation Linked AF Point Selection. I experimented with this on my 7Ds and found it seemed to slow thing a little, so I turned it off.
I haven't noticed that this slows things down at all, neither on the 7D nor the 1DX. It most definitely speeds up handling, compared to manually moving around the AF points when you change orientation. Especially for me, who often try to take photos of runners, first approaching in a way that's OK for horizontals, then when they come close I switch to verticals on the fly, and immediately have the appropriate AF points selected.
amfoto1 wrote in post #16304026I can't think of any time I'd want the camera to display all points, all the time (1).
When you set AF selection to continuous, i.e. you can wrap over from the left side to the right, without having to go all the way back, across the screen, this allows you to see if you are actually at the rim or not.
Whether you like that or not, that's up to you, but it's a possible reason to display all points.
amfoto1 wrote in post #16304026Optionally, you can swap the functions of the AF On and * buttons. I do this because I prefer to use the larger, more prominent * button for focusing, and the AF On button for less frequently used AE Lock (that's normally assigned to the * button).
Have they not got this right on the 70D? I know that my first camera having the AF-ON button (the 40D, which came right after the 1D Mark III, where the feature was introduced) had a smaller AF-ON button than the * on. It's still like that on the 7D, but now on the 1DX Canon has finally figured this out, and made the AF-ON button larger and more prominently placed. It's the first thing you press with your thumb, when holding your camera. Are you saying the 70D repeats this mistake, making the AF-ON button small, from older models?
Here I'm holding the 1DX, and the right thumb is right over the AF-ON button by default, so to speak.
YashicaFX2 wrote in post #16303900I'd like you to back up your claim that the 70D does NOT have a dedicated AF chip. The absence of data is not data of absence. I believe the 70D does have a dedicated AF chip. It is pumping out nearly the same amount of data (20MP vs 22MP), at a faster rate (7fps, vs 6fps) than the 5DIII does. (5DIII: 132 mb/s, 70D: 140 mb/s) If the 5DIII is using an AF chip, it seems almost obvious that the 70D is using an AF chip. If the 70D doesn't NEED one, neither does the 5DIII. Canon is not in the business of adding un-necessary parts to their cameras. Back up your claim.
If there's a dedicated AF CPU in the 70D, and Canon doesn't say so in their marketing material, then that would be the first time in the history of the EOS camera system. Everything can happen, but it sounds extremely unlikely to me.
This has nothing to do with how many Megabytes of data the camera processes for every picture. According to the processor architecture (for cameras where Canon has made pretty detailed descriptions of this, even down to CPU clock frequencies), the CPU handling the image data isn't the same as the one doing AF, regardless of whether there's a dedicated processor for AF or not. It's just that when there actually is a dedicated CPU for AF (when that task isn't handled by the sequence control CPU), there's more processing power available to compute AF lens movement during the short time the mirror is down, and thus the likelihood that the continuous drive speed slows down due to AF is minimized.
What's more relevant to look at, when the camera is performing Servo AF during high speed continuous shooting is the total number of focusing elements to evaluate. A cross type AF point has two elements, a linear only one. The we have to look at what there is to measure when the camera is using all points, since that's the most taxing mode.
Compared like that, the 7D/70D has 40 elements, the 1D Mark IV 64, the 5D Mark III/1DX 112 focusing elements. We also know that when using all points on a 1D Mark IV, it doesn't really do that, but creates a "cloud" of 18 assist points around the active one, and then move the "cloud" as the tracking point changes. It's obviously not capable of processing all elements at the same time.
The 7D does the same, although Canon don't tell you in their documentation. But when using all 19 AF points, it doesn't use all 40 focusing elements, but convert most of them to linear points. It's easy to prove, when making targets with pencil lines on white paper, and you find that even the most obvious contrast can't be found by supporting AF points when it's in the wrong orientation. But select that particular point as a single AF point, and it has no problem at all to see the contrast, since then it's cross type.
Finally, I don't know any specifics about what Canon have changed between AI Servo AF II algorithm (introduced with the 7D & 1D Mark IV) compared to the AI Servo AF III they use now (from the 1DX & 5D Mark III). They'll never tell us the details, of course, but they do of course brag about it in their marketing material, where they state that the 1DX is better than any 1D-series camera ever before. Of course.
It is most certainly different, since the 1DX now supports not only the time-out setting (confusingly enough called sensitivity), but also acceleration and sideways movement (AF point switching) agility. They also offer three settings for drive speed vs. focus priority for Servo AF and two settings for One Shot AF, where the previous AF algorithm had two and one, respectively.
So there are changes, but if a non-dedicated CPU, running the AF algorithm, is more efficient when that executes the Servo AF III calculations than a dedicated CPU running the Servo AF II formulas, we'll never know. I'm not even sure Canon's R&D people can give a definite answer, since it most likely depends upon a lot of conditions, which are difficult to control. At least out of the laboratory, where most of us take our pictures.
It's not particular to the AF points, but after reading a bit in the user's manual for the 70D, I've realized that it doesn't suppor the immediate change of AF settings you can get with the 7D, just by holding the depth-of-field preview button (appropriately reprogrammed, of course). This quick change of the setup I've found very useful when trying to follow an athlete coming running towards you, since what kind of target he represents changes dramatically when the distance closes in. The 1DX also supports this functionality, and I use it with that camera too.
Now being spoiled by the viewfinder of the 1DX, I still see that the 7D sports a 100%, 1X pentaprism viewfinder, where the 70D has a 98%, 0.95X pentamirror viewfinder.
For that alone, I can live with if the 7D has inferior image quality at high ISO, since the viewfinder will at least help me make sure I have the composition right.
