I shoot a Canon 7D, mostly static subjects such as dragonflies, spiders, and perched birds. I use back-button AF and typically a single focus point placed as close to the eye of the subject as possible. I am usually handholding or monopod mounted at 200-300 mm with IS lenses and I try to keep shutter speeds roughly equal to or at least ½ my focal length. I am set to high-speed continuous shutter release and AI-Servo. I acquire focus with the back button (AF-ON) and keep the button depressed while I activate the shutter and fire off a burst of 3-4 shots.
When I look at the 3-4 exposures within a burst on the computer monitor, I see subtle differences in focus sharpness. What is happening when the subject is not moving under a single AF point? I assume one possibility is that I am moving the camera slightly from one exposure to the next within a burst. If that is the case, does the camera try to refocus for each exposure within a burst or is it locking exposure when I first depress the AF-ON button and retaining that same focus during the entire burst? If the camera is trying to refocus between shots within a burst, would I be better off using slow speed continuous burst rate to allow it more time to adjust focus?
I think I understand what AI Servo is trying to do when the subject is moving or when there are multiple AF points activated and focus is being handed off from one point to another. It is less clear to me what is happening when I am using a single AF point on a static target. Should I be using AI-Focus mode for this kind of work rather than AI-Servo? Am I making this more complicated than it really is? Thanks for your help.
PS – does your answer also apply to the 7DII, which I hope acquire in a few months?
When I look at the 3-4 exposures within a burst on the computer monitor, I see subtle differences in focus sharpness. What is happening when the subject is not moving under a single AF point? I assume one possibility is that I am moving the camera slightly from one exposure to the next within a burst. If that is the case, does the camera try to refocus for each exposure within a burst or is it locking exposure when I first depress the AF-ON button and retaining that same focus during the entire burst? If the camera is trying to refocus between shots within a burst, would I be better off using slow speed continuous burst rate to allow it more time to adjust focus?
I think I understand what AI Servo is trying to do when the subject is moving or when there are multiple AF points activated and focus is being handed off from one point to another. It is less clear to me what is happening when I am using a single AF point on a static target. Should I be using AI-Focus mode for this kind of work rather than AI-Servo? Am I making this more complicated than it really is? Thanks for your help.
PS – does your answer also apply to the 7DII, which I hope acquire in a few months?
