Choosing AF-S over AF-C

When photographing birds in flight, there are times when choosing AF-S over AF-C can make sense. Let’s have a look at a recent image run of a blue jay taking flight to illustrate this idea.

It is important to state up front that the technique discussed in this article is applicable for a wide range of cameras. It tends to work best with cameras that have high frame rates when shot in single auto focus (AF-S) mode.

For example, Nikon 1 bodies like the models that I own (V2, V3, and J5)  as well as my Olympus OM-D E-M1X can all shoot at up to 60 frames-per-second in AF-S mode. I’m not up to date on the latest camera specifications, but I assume a number of other cameras are also capable of very fast AF-S frame rates. When using the AF-S single auto focus option, the cameras noted set focus and exposure based on the first frame of the image run.

In certain situations with bird-in-flight images you can use this ‘first frame focusing’ to your advantage.

Often when a potential subject bird is perched in a tree or bush it is partially obstructed by branches. These obstructions can sometimes confuse the continuous auto-focusing (AF-C) of our cameras. This can cause the subject bird to go out of focus as it flies past branches in the foreground of our composition if our cameras lock onto the branches when AF-C is used. Let’s see how choosing AF-S over AF-C can help overcome this issue.

NOTE: Click on images to enlarge.

Olympus OM-D E-M1X + M.Zuiko PRO 40-150 mm f/2.8 with M.Zuiko MC-20 teleconverter @ 300 mm, efov 600 mm, f/5.6, 1/2500, ISO-800, Pro Capture H mode, subject distance 12 metres

We can see that the blue jay in the photograph above is signalling its intention with a pre-flight crouch. The head of the blue jay is obstructed by branches so we would not typically try to photograph this particular bird in flight. However, there are some important details that we can quickly assess to realize that this is actually a good bird-in-flight opportunity.

The first is that the blue jay’s head is pointed forward and slightly tilted to its right. This is an indication that when it takes flight the blue jay will have a flight path that will likely remain parallel to the focal plane of my camera. This means that the blue jay will remain in focus even though AF-C is not being used.

If we look quickly to the right of the blue jay we see a good break in the branches. This is the area of the composition where we can anticipate capturing our bird-in-flight images. So, we can position the blue jay on the left hand side of the composition, thus allowing it to fly into our intended bird-in-flight composition.

The body of the blue jay is clearly visible. We can place a single AF-S point on the shoulder, back or belly of the bird. As long as we use an appropriate aperture to achieve sufficient depth-of-field, and the blue jay takes the flight path we think it will… we should end up with some usable images.

When using a camera that does not have Pro Capture H, you would start your run of AF-S photographs as soon as the bird goes into its pre-flight crouch, or physically launches from its perch. This assumes that the buffer on your camera is deep enough to store a sufficient number of images.

Let’s see what happened when choosing AF-S over AF-C with this image run.

Olympus OM-D E-M1X + M.Zuiko PRO 40-150 mm f/2.8 with M.Zuiko MC-20 teleconverter @ 300 mm, efov 600 mm, f/5.6, 1/2500, ISO-800, Pro Capture H mode, subject distance 12 metres

The blue jay begins to launch…

Olympus OM-D E-M1X + M.Zuiko PRO 40-150 mm f/2.8 with M.Zuiko MC-20 teleconverter @ 300 mm, efov 600 mm, f/5.6, 1/2500, ISO-800, Pro Capture H mode, subject distance 12 metres

It is propelling forward with its head starting to become visible…

Olympus OM-D E-M1X + M.Zuiko PRO 40-150 mm f/2.8 with M.Zuiko MC-20 teleconverter @ 300 mm, efov 600 mm, f/5.6, 1/2500, ISO-800, Pro Capture H mode, subject distance 12 metres

We have our first potentially usable image with the blue just leaving its perch…

Olympus OM-D E-M1X + M.Zuiko PRO 40-150 mm f/2.8 with M.Zuiko MC-20 teleconverter @ 300 mm, efov 600 mm, f/5.6, 1/2500, ISO-800, Pro Capture H mode, subject distance 12 metres

Here is our second potentially usable image with the blue jay fully launched and its wings spreading…

Olympus OM-D E-M1X + M.Zuiko PRO 40-150 mm f/2.8 with M.Zuiko MC-20 teleconverter @ 300 mm, efov 600 mm, f/5.6, 1/2500, ISO-800, Pro Capture H mode, subject distance 12 metres

The blue jay’s head is partially obstructed in our last sample image, making it probably unusable for many photographers.

Choosing AF-S over AF-C can help us capture usable images of birds-in-flight when subjects are perched in trees and bushes. We need to anticipate the bird’s direction of flight. Time our shutter release with a pre-flight crouch. And, allow the bird to fly into a relatively unobstructed area in our composition.

Technical Note:

Photographs were captured hand-held using camera gear as noted in the EXIF data. Image were produced from RAW files using my standard process. All photographs are displayed as 100% captures without any cropping.

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4 thoughts on “Choosing AF-S over AF-C”

  1. Tom,

    Even if I don’t have an Olympus camera, I understand why you opted for AF-S in this particular sequence, which happens to be one of my favorites in one of your recent posts. Amazing how the blue jay takes off in between the branches, knowing how much flap space he has 😀

    Oggie
    http://www.lagalog.com

  2. Tom
    With the Pro H feature always using only the first photo for focus, would there ever be any reason to use AF-C with Pro Capture H?

    Joel

    1. Hi Joel,

      If a photographer wants to use AF-C with Pro Capture then they would choose Pro Capture L with a maximum frame rate of 18 fps. Using AF-C with Pro Capture H is not an option. In this mode Pro Capture H locks the exposure,focus and white balance with the first frame.

      Tom

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