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Frequent Contributor
Posts: 49
Registered: ‎06-18-2013

Question about 70D and AF points with AI Servo

I like getting photos of birds in flight so fast, reliable focus  and maintaining focus are important. Based on a recent experience I have this question:


I typically like using the 9 center zone AF points for automatic focus on fast moving birds. Typically works great, especially if only sky in the background. When I was panning some fast flying ducks with trees in the background using the highest rate of capture the first photo was almost spot on focus on the ducks, second was spot on, and after that the ducks were out of focus on this flight. If the subject originally focused on moves outside the selected center 9-AF points zone should focus still be maintained or did I lose it while panning these ducks? In other words will AI Servo use the other AF points if the subject (or my inferior panning ability) has not been maintained within the AF zone I selected?


I assume the best remedy for this is to select all AF points and try my best to get the subject on the center AF point when focusing?


How does the 7D Mark II compare with the 70D on this? Is the 7D M II more versatile in allowing additional AF points to be engaged in AI Servo?



Reputable Contributor
Posts: 790
Registered: ‎06-11-2013

Re: Question about 70D and AF points with AI Servo

You are correct that the best solution is to switch to Single Point and work to keep that right where you want the camera and lens to focus. When shooting against a plain background, the multi point settings can work (either Zone or All Points/Auto on your camera).


You also might try changing the settings for AI Servo Tracking. There is Custom Function II-1 Tracking Sensitivity that controls how quickly the camera "jumps" to a different target. Try reducing that (i.e., set it -1 or -2). This doesn't change the speed with which AI Servo acquires a subject or tracks it in most situations. However, with is set to the minus side on my 7D I have noticed that sometimes the camera will be more inclined to lose focus if  a subject changes direction quickly... in that case I dial this setting back up (even in to the +1 or +2 range). However, your camera also has Custom Function II-2 Acceleration/Deceleration Tracking, which can be dialed up to help the camera better deal with subjects that change speed and/or direction.


Other Custom Functions that might help are C.Fn II-3 and C.Fn II-4, which govern 1st image focus priority and 2nd/subsequent image focus priority. On my 7Ds I set these to Focus Priority, which can prevent an image from being taken if not in focus. This slows the camera down at times, but I don't need images that aren't in focus anyway. I might set these differently if shooting with wide angle or at small apertures, with more depth of field that covers slight focus errors.


Both 7D and 7D II have a couple AF patterns that your camera doesn't have.


Like all Canon, your camera has Single Point/Manual and All Points/Auto.


In addition, your camera has Zone Focus (9-point, which is like a reduced size All Points/Auto... any AF point in the Zone can start focus or pick it up from the adjacent one if needed when the subject moves).


7D has same as yours, but also has:


- Single Point Spot Focus (uses a smaller AF point, good for high precision, but a little slower focusing).

- Expansion Points (allows focus to "pass off" to an AF point that's adjacent to the primary one that was selected)


7DII has all the same as the 7D, but has:


- Two versions of Zone Focus: Large (right/middle/left, up to 25-points) and Small (15-points).

- Two vesions of Expansion Points: 4-point (up/down, right/left) and 8-point (up/down, right/left, plus diagonal)


Your 70D and the original 7D use a 19-point AF array that's all "cross type" and is f5.6 capable. The 7DII has a 65-point array, all "cross type", center point is f8 capable.


Both 7D models also might be a bit faster focusing and better tracking because, like 1D models, they use a discrete chip to drive AF, in addition to dual processors that handle images separately. AFAIK, all other Canon models - including your 70D - share AF duties through a single main processor that 's also handing images.  


7D II has focus "Cases", which are essentially presets for particular types of situations. It also has a few more focus tweaks via the menu and custom functions.


So, in answer to your question, yes the 7DII has a more versatile AF system than your 70D or my original 7Ds, but it also is much more complex to set up and use. I'd suggest you continue to work with your 70D, to learn to get the best out of it. Eventually you might want to "graduate" to the 7DII, for the additional features. Or maybe you'll find the 70D does all you need a camera to do.




Alan Myers

San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories




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