7D Tracking & Focus.

[Ed_]

Hello All,


I have been browsing this forum for several months and loving every minute of it! Thanks to everyone for building such a great resource!This is my first post, I have a 7D with 70-200 f/4, 24-105, and the 50 1.8. I moved up to the 7D from a XT then XTi. My question is what auto focus point/selection should I use when I am in Ai-Servo mode. I normally set my focus point to the center or af-expanison and readjust to compose the scene. I want to be able to follow the rule of thirds and still catch the action, but it seems to hard to predict the action and compose off center with Ai-Servo.


Any Thoughts?

[neuroanatomist]

Hi Ed, and welcome to the TDP Forums!


In AI-Servo mode, you can use any AF point as the starting position for tracking. So, for example you can use AF Point Expansion, manually select an off-center point, and that point (or the immediately surrounding ones) will be used to start tracking. Even when you're in 19-pt AF mode (the outer brackets), when you select AI-Servo mode you can choose an AF point using the joystick (seems odd to select and AF point in 'auto AF mode', I know, but that's how it works, and note that you're only selecting the point to start tracking - the AF system will use all 19 points as needed as the subject moves through the frame).


Also note that the 7D is different from previous non-1-series bodies for the starting point of AI-Servo tracking. With your previous cameras, you needed to start tracking with the subject in the center, but with the 7D you can start tracking from any selected AF point.


Hope that helps...


--John

[Ed_]

Thanks John, That does really help.


What is the best practice with following the general rules of framing and capturing the action in focus.?

[neuroanatomist]

I want to be able to follow the rule of thirds and still catch the action, but it seems to hard to predict the action and compose off center with Ai-Servo. ...What is the best practice with following the general rules of framing and capturing the action in focus?

In terms of composition for action, you can use the rule of thirds - when doing so, try to place the subject with 'room to move' (i.e. so the 2/3 of the frame is in front of them as they move).


Getting sharp focus is mostly about technique and knowledge, and depends on what sort of 'action' you're trying to shoot. If it's sports, knowing the sport is one of the best ways to improve your shooting - that will help you to better predict where the action will be (e.g. when a base runner is likely to run/steal/slide). If it's wildlife, learn the habits of the critters you're shooting - some birds fly in straight lines, some zig-zag.


The other element is the AI-Servo performance of your camera - and the 7D is pretty good in that regard. It's also very customizable, so take the time to learn the AF-related C.Fn's. There are a couple that deal with changing subjects (Tracking Sensitivity and Tracking Method). Depending on what you're shooting, you can set those differently. For example, in a football game where I wanted to take pictures of a specific player, those C.Fn's would be Slow and Continuous so that the AF would remain on the subject and not switch to another player as he ran into the field. But, if I was shooting a footrace and wanted to focus on the leader, Fast/Main Point would cause the AF to switch to a different runner as s/he took the lead.


The other thing your 7D's AI-Servo will do better than the Rebels you've used is track action moving toward/away from you. The Rebels are ok with action moving across the scene, but not as good at diagonals and head-on movement. The 7D is much better (but still not up to a 1DIII/IV). So, again depending on what you're shooting and your access, you might try a different position (e.g. for football, at the back of the end zone with your 70-200mm).


One final tip - if you don't already do this, try learning to shoot with both eyes open. The 7D has a 22mm eyepoint (meaning your eye can be 0.85" from the viewfinder and still see the whole image). If you back your eye off from the eyecup a little bit, you'll have room to see more of the scene with your other eye (which will have a wider angle of view unless you have a lens shorter than ~30mm) - that can help you anticipate when a subject is about to enter the frame.


--John

[Ed_]

Thanks for the info I will practice with my family and see how it goes.

[erno james]

Hey Ed,


On my 7D, I've been using the back button focus button (AF-ON). This decouples autofocus from the shutter button. It's useful for framing subjects in motion. I have been shooting indoor sports and this allows one to AF the subject using the back button. Once your subject is in focus, you can then let go of the button once AF is achieved, recompose your shot, and then fire the shutter button any time you like. It's a nice way of not having to half-press and hold the shutter button. Using this form of AF, I generally keep the camera in AI-Servo all the time. One cool bonus is that when you hand your camera off to one of your friends, they have no idea how to use it! jk.





This is from Canon's website called the Digital Learning Center: http://www.usa.canon.com/dlc/controller?act=GetArticleAct&articleID=2286

[neuroanatomist]

Using this form of AF (back-button/AF-ON with shutter release set to meter only), I generally keep the camera in AI-Servo all the time.

I also routinely use AF-ON for focus. Just be aware that AI-Servo stops tracking once you release the AF-ON button, just as with the shutter release in 'normal' (half-press) focus. Likewise, if you have an IS lens, IS will shut off when you release the AF. Keep in mind that IS takes ~0.5s for full stabilization on most lenses. I do like that with back-button AF, a half-press of the shutter will re-activate IS (and meter) without affecting focus.

[erno james]

One more thing Ed, go to Canon's website and go to the Digital Learning Center. There is a dedicated EOS 7D link that shows these little vidoe vignettes (not vignetting) that includes various focusing modes. You can even download them on a CF card and carry them around in your camera for future on-site reference.


take care, erno.

[Ed_]

Thanks Erno, That makes a lot ofsince, I will give that a try!