AI Servo with Action Shots | Photography 101
When tracking motion, focus can make or break the success of the shot, and using AI Focus may be a convenient choice but won’t always give you tack sharp focus. In this excerpt from Photography 101, we show you exactly why AI Servo, or Continuous Servo, yields the best possible results when capturing action.
Using AI Servo in conjunction with Single Point AF
In order to be as accurate as possible, select a single AF-point that is in the general vicinity of your action while still shooting in Continuous Servo AF. If you aren’t sure exactly where you want to want to be focusing, choose an area option because it will give you a little bit more leeway to get the focus.
Quick Tip: Depending on your camera, you are going to have different area options when it comes to AF. For example, on a 5D Mark III, we can enter into the select AF area mode and when you are using the single AF point, we can actually expand the AF area to surround, or create zones around that AF point.
If you want to have spot level AF control but then you want a little more leeway for a moving subject, you might use a Spot AF with an AF Area Surround, which will use all the points around that selected AF point to focus. That is a lot of AFs to talk about.
These types of modes give you a little more room for error, but remember that they also come at a cost, because you lose a little bit of control over which exact point is being used for focusing. It might not be something that you want to use when you are shooting a portrait because in portraits, we generally want to use the accurate single point AF for focusing, but a larger AF area might be useful when you are shooting moving objects.
Center Point is Always the Strongest
With Continuous Servo, always be careful because your center point is always going to be the strongest AF point on your camera. This means that if you are using a center-based composition, AI Servo typically will work best.
When you are using AI Servo, using any outside AF point means that you are more likely to get a lot of misfocused images. During a wedding processional—even when they are coming straight down the aisle—we still would often use single-shot focus, because we would rather shoot and refocus on every single shot, have one or two that are misfocused, and let AI Servo handle it rather than miss a bunch of them.
Continuous Capture Leads to Buffer Time
We shoot at a continuous high speed in order to utilize the strength of Servo mode, capturing a slew of images in a matter of seconds to ensure that we got the shot, because at least one of those images, if not all, has to be tack sharp.
Because of this constant firing, after every 5-6 images the camera will cease fire (especially if we are shooting in RAW) as it writes the images to the memory card. If you are in need of quantity, dial in the closest accurate settings of your scene and switch to JPEG to record more images to your memory card.
Hopefully, this video demonstrates the differences between single shots and Servo modes, the strengths of each of them, which situations work best for single shot vs Servo, the overall weaknesses, and the situations where these modes might have a hard time.
For more info on focus modes & basic camera functions check out Photography 101, your A-Z guide to the foundations of photography. Our Premium membership holds access to this workshop and more to advance your photography education.