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Camera: Canon 700D
Lens: EF-S 55-250mm STM

So far I have been shooting still subjects. But recently I wanted to photograph moving people (skaters).

I changed the AF mode to AI-Servo (as skaters are obviously moving all the time) and started taking photos.

To my surprise, the green focus confirmation dot that normally appears at the bottom right of the viewfinder did not fire up at all! I read the camera manual and this is a known feature. The focus confirmation light indeed does not work in AI-Servo mode.

I am a bit puzzled now. How am I supposed to know if my shot is in focus? Am I supposed to "spray and pray" that I get good shots?

Or there is some other camera setting that I am not aware of?

Update: By "focus confirmation dot" I am not talking about the red focus points. I am talking about the green confirmation dot that appears at the bottom right of the viewfinder that says to me "focus has been achieved".

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The reason the focus confirmation light does not function in AI Servo mode is because the camera never stops tracking the subject and adjusting focus as necessary. The green focus confirmation light in the lower right corner of the viewfinder is an indicator that AF has been locked and has stopped measuring focus. That's the last thing you want to happen in AI Servo mode! With a moving target the green light wouldn't guarantee your subject is in focus, it would only confirm your subject was in focus at the distance it was from you when the AF was locked.

With the appropriate menu selections with some (but not all) Canon models the viewfinder can be set up so that when doing tracking of moving subjects the focus points currently in focus are the only ones appearing on the LCD overlay visible in the viewfinder. Models that have such capability include the 1D X, 1D X Mark II, and 7D Mark II. The 700D, as a more budget oriented model, does not feature an RGB+ir light meter and the processing power needed to run Canon's iTR (Intelligent Tracking and Recognition) AF in concert with the PDAF sensor.

Since your camera lacks the capability of the iTR AF, your best option is to do it the old fashioned way: use your eye pressed to the viewfinder to confirm your subject is in focus. Do note that if the camera can't focus on something it will warn you by rapidly flashing the green AF confirmation light. The more you practice it the better you will get at seeing what the AF system is really targeting and seeing when your subject is the center of focus.

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  • Cool. The real answer is in your last paragraph. Not having the confirmation light on means that things are more or less ok, while having a rapid flashing light means things are not ok. I have tried this with my camera and I confirmed it already. – kazanaki Jun 8 '16 at 7:51
  • The confirmation light never really confirms that your intended subject is in focus. It just confirms that something is in focus and that the AF system has locked focus. – Michael C Jun 8 '16 at 10:37
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The focus confirmation light indeed does NOT work in ai-servo mode.

It would be cool if the focus confirmation dot acted like a missile target lock indicator, but it doesn't. It just tells you that the AF system has attained the best focus it can. In AF Servo mode it never reaches that point because the subject may move.

How am I supposed to know if my shot is in focus? Am I supposed to "spray and pray" that I get good shots?

How would you know if your shot is in focus anyway? If the light turned on every time the camera achieved focus within some given tolerance, it'd still take you around 0.2 sec to react, and by the time you released the shutter the subject could easily have moved out of focus again. The AF system is incredibly fast, and if you can keep your chosen AF point on the subject, it'll do a far better job at maintaining focus than you could by hand. Here are some tips for getting good shots of moving subjects:

  • Use a fast shutter speed or flash with second curtain sync to avoid unwanted blur.

  • Use a tripod or monopod to help steady the camera. It's a lot easier to track a moving subject smoothly and keep that AF point on target if you can work from a stable platform.

  • Shoot often. Even if the AF system does a perfect job, your moving subject will look better in some positions than in others. Shooting in continuous mode can improve your odds of getting the shot you want.

If you want to call that "spray and pray," that's up to you. The reality of shooting a moving subject is that not every shot will work out. With AF Servo mode, keeping the subject in focus is usually the least of your problems.

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  • With Canon EOS cameras any shutter speed faster (shorter) than 1/30 second will use 1st curtain sync, even if 2nd curtain sync is set in the menu. Canon is very open about this. Other manufacturers seem to do the same (or similar at slightly different threshold speeds) without informing the user that they do such. – Michael C Jun 8 '16 at 6:58
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    With Canon bodies that feature iTR the AF point indicators can be set to show only when they are in-focus. This has the effect of different AF points lighting up as the subject is tracked as it moves around the frame. It functions very closely to "missile lock" in that respect. – Michael C Mar 16 '17 at 21:18
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The camera is continuously focussing, so it doesn't really make sense to indicate which focus point is active. It would potentially be changing all the time, which could be distracting, or the camera could illuminate one focus point, the subject could move and the camera re-focusses using another focus point and the user might think that when they took the shot, the subject was not under the illuminated point and that focus was missed.

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  • I am not talking about the red focus points. I am talking about the green confirmation dot that appears at the bottom right of the viewfinder that says to me "focus has been achieved". I updated my question to make it more clear. – kazanaki Jun 7 '16 at 9:46

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