I Need Some 600EX Help

So tonight's Halloween and I headed out with my 5d MK3 with my 600EX-Rt attached. The problem that I was having is that I had no focus assist beam and even though I have focus priority (will not take a pic until focus is achieved) set on, it would still take the shot before focus lock happens. Focus assist is set to on by the way. Did I miss something in the set up with my 600EX? I consider myself an advanced amateur but this really had me stumped. If any one can help I would appreciate it. Perhaps I have a bad flash but that doesn't happen very often. Thanks again in advance for your help guys and gals.

Autofocus mode must be set to One Shot, not AI Servo.

Curtis N wrote in post #15193302
Autofocus mode must be set to One Shot, not AI Servo.

^^^^+1

Curtis N wrote in post #15193302
Autofocus mode must be set to One Shot, not AI Servo.

That's it! I so hardly use anything but one shot that I never even considered that. Thanks Curtis.

Is there a specific reason Canon disables focus assist beams with servo? I can't think of a technical reason (of course that does not mean there isn't one) why it would not work but I can definitely think of instances it would be a benefit (any poorly lit subject that is moving).

Since servo AF is continuous, the AF assist beam would have to be continuous as well. Neither the batteries nor the bright LEDs used for AF assist in the flash are designed for this, I presume. You need to bring a separate searchlight for this.

I think that it has something to do with the fact that the focus is continuous and never locks onto a(presumably) moving object in AI Servo...The red beam is to help the AF system find a focus lock for a stationary subject in One Shot AF only...Still you'd think that the red beam(if it had the capability for continuous use) could at least provide illumination to help find the moving subject...Oh well, an assistant holding a flashlight still works.

Yes, which shows that the red beam would work too, if it was designed to be on for a longer time. But it isn't.

apersson850 wrote in post #15196118
Yes, which shows that the red beam would work too, if it was designed to be on for a longer time. But it isn't.

I also think that it would be nice to select whether or not the camera will take a shot even though it doesn't have a focus lock.

ears wrote in post #15196217
I also think that it would be nice to select whether or not the camera will take a shot even though it doesn't have a focus lock.

AI Servo IS designed this way, it has release priority rather than focus priority...But again, the red beam will not fire. So at least for now you can't have both.

Try sending your suggestion to Canon.

rrblint wrote in post #15196667
AI Servo IS designed this way, it has release priority rather than focus priority...But again, the red beam will not fire. So at least for now you can't have both.

Try sending your suggestion to Canon.

I want focus lock priority with the flash attached and in AI servo mode but the camera overrides it and switches to release priority regardless of how I have it set. I am sure that there is a reasonable explanation for this but it is probably far too advance for me to comprehend.

ears wrote in post #15196773
I want focus lock priority with the flash attached and in AI servo mode but the camera overrides it and switches to release priority regardless of how I have it set. I am sure that there is a reasonable explanation for this but it is probably far too advance for me to comprehend.

AI Servo is by definition continuous auto focus, it never stops focusing as long as the AF button is pressed or shutter button is half pressed(depending on how the camera is set up) and therefore cannot lock. Since the focus never stops or locks, the shutter can be released at any time. Focus lock can only be achieved in One Shot AF where the camera assumes that the subject is stationary(even if it isn't) and stops focusing once best focus is achieved. One Shot AF has focus priority and therefore the shutter will not release until focus lock is achieved. The down side of this is that if the subject moves after focus lock is achieved, then it will likely be out of focus by the time that the shutter is released.

Now all this is blurred a bit by the fact that Canon have settings in their cameras for focus priority, equal priority or release priority for AI Servo AF, as well as settings for focus priority and release priority for One Shot AF, in the most recent cameras (like 1DX).

But in principle you are right.

Thanks Anders for the info, I'll have to read up on these updates to the more modern(and expensive lol) cameras, but from what you say, this sounds like good progress.

I once asked the question why the AF assist beam can't work in AIServo, and someone answered that the red pattern projected on the subject would then show up in the picture.