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by Roger N. Clark
I am often asked how I set up my camera to do action photography. Here is my strategy. The key to fast autofocus and focus tracking is the use of phase detection focus.
The Action Photography Series:
I am often asked how I set up my camera to do action photography. Here is my strategy (I use a Canon camera so I'll cite the specific modes on Canon cameras); other cameras have similar settings and many can also take excellent action photos, so please do not take these descriptions as endorsing Canon, nor that only Canon cameras can do this type of photography).
The key to fast autofocus and focus tracking is the use of phase detection focus. This is a method where two or more small apertures are used to mask the light from the lens at an out of focus position. The sensing system can detect the direction and amount the image is out of focus, and command the lens to move to the proper position. No second check is necessary in most cases. Such phase detection systems are generally available on single lens reflex (SLR) film and digital cameras. Few point and shoot cameras have phase detection autofocus. The time to raise the mirror in an SLR is small compared to alternative methods (e.g. contrast detection autofocus) so SLR cameras currently have the fastest autofocus. More on autofocus can be found at:
Combining the rapid measurement of focus error and magnitude with its rate of change, allows modern SLR cameras to use predictive autofocus. Predictive autofocus tracks the change in focus position, usually assuming a linear velocity, and from the known time it takes to raise the mirror and open the shutter, predicts where the focus should be when you press the shutter button and the camera actually takes the picture. It is this property that makes the modern SLR and DSLR ideal for action photography. Point and shoot cameras with contrast detection iterative focus checking are very slow in comparison to SLRs and DSLRs, although the former are usually more expensive. The faster the camera, the faster the electronics and mechanical movements must be, driving up costs.
With that introduction, here is how I do action photography.
Use Manual Exposure mode for subjects in constant light You set aperture to control depth of field and also set the shutter speed. If the subject is in constant light and moving with changing background (e.g. sky to trees) or against a very different intensity background (e.g dark bird against cloudy-bright sky), manual mode gives the most consistent results. Check exposure by monitoring the histogram. For maximum speed, open the aperture all the way (smallest f/number). If you have a short enough exposure time to stop the action the way you want, you can close the aperture a bit to increase depth of field or lower the ISO.
Use Aperture Priority mode only if the light on the subject is changing (Av on Canon cameras). For example, if the subject is moving in and out of shade. You set aperture and control depth of field and speed. For maximum speed, open the aperture all the way (smallest f/number). If you have a short enough exposure time to stop the action the way you want, you can close the aperture a bit to increase depth of field.
Use Predictive Autofocus (AI servo on Canon cameras). Predictive autofocus tracks moving subjects and sets the focus point predicting where the subject will be after the delays in raising the mirror and actually opening the shutter.
Use one focus point: A common mistake in action shots is to use multiple Auto Focus (AF) points, then the camera confuses the subject and often locks on to something you don't want. Use one focus point and keep that AF point on the moving subject so the AI servo can track it. The AF system has trouble with contrasty back lit subjects, so try and choose well lit subjects and/or backgrounds that are smooth (like birds with blue sky background).
Set ISO to stop action if that is what you want. Depending on the speed of the action, you may need 1/500, 1/1,000, or even 1/2,000 second exposure time. 1/200 sec. only works for pretty slow movement, unless the subject is very small in the frame.
Example: Eagle in Flight
A pair of eagles were moving down the beach, fishing, on the Kenai peninsula in Alaska. I moved ahead of the direction of travel and got onto the beach with my gear. An eagle landed not far from me. I moved diagonally toward the eagle, acting like I was walking along the beach not paying attention to the eagle. The eagle was aware of me but never made any moves to indicate it was stressed. I positioned myself where I thought the eagle would take off and fly generally in my direction. I got in position several minutes before the eagle took off.
This image was made a 500 mm f/4 L IS lens with the now discontinued Canon 1D Mark II, but now for images like
this usei a
Canon EOS 7D Mark II DSLR Camera with a
Canon EF 300mm f/2.8L IS II USM Lens.
and have better tracking and more detail on the subject.
This example uses a bald eagle starting from a sitting position, then taking off and flying past me.
The camera used was a Canon 1D Mark II with a 500 mm f/4 L IS lens plus a 1.4x teleconverter, giving 700 mm at f/5.6. The 1D Mark II is a 1.3x crop sensor, so at 700 mm the field of view is 2.23 x 1.56 degrees. The ISO was 400 and exposure times varied from 1/1250 second to 1/1600 second except the last frame (Figure 24 below) was 1/500 second. The camera and lens was mounted on a carbon fiber tripod (which is very good at reducing vibrations), using a Wimberly (gimbal) head. The camera and lens were well balanced to that they would easily move in both directions and would stay point in the same direction if I let go. It is the superb balance that allows ease of tracking a moving subject with a long telephoto lens. Image stabilization was on. I only turn off image stabilization if I lock the axes so the lens only points at a static subject.
My goal was to get the eagle in close to full frame flying with its wings outstretched. Critical to a successful wildlife photo is to have the eyes in focus. So, with the eyes in focus, and the wings in a nice V shape, I thought the body of the bird would be below center for this image, so I set the camera for one autofocus point below center. This meant I needed to keep the one autofocus square on the eagle's eye. But at the long telephoto length, one autofocus square is only 4.5 x 6.4 arc-minutes on the eagle. That is about the size of a U.S. quarter (2.4 cm diameter) at a distance of 20 yards (18.3 meters). When the subject is close so it fills the frame and is moving fast, the angular turn rate is high, making pointing with such fine accuracy difficult. That will make it hard to keep the autofocus rectangle positioned perfectly. Below shows how I did. Keep in mind, this was the first try of the day.
The images below show the full frame of the 1D Mark II camera and the 45 focus points. The focus point in use is colored in red. These images are screen grabs from zoombrowser and do not have a color managed work flow done.
I know at this time that the bird is about to pass very close to me. Not wanting to risk getting the wrong wing position or filling my buffer and missing the close shot, I keep my finger on the shutter, pressed half way so the autofocus system continues to track the bird. I wait for the bird to move into position and frame one shot (Figure 24, below) when its wings are in the raised V position.
Conclusions
The predictive autofocus tracks the changing distance to the camera quite well. With long focal length telephoto lenses, the corresponding narrow field of view makes it difficult to track a fast moving subject. Even so, with the lens and camera balanced on the gimbal head, out of 24 frames shot, 22 had the bird's head and eyes in focus, for a 92% success rate on the first tracking attempt of the day (with the error mine and not the camera's). And more important, the closest images, with the distance and angular rates at their maxima, have excellent focus and sharpness on the head and eyes. Acquiring the bird at a great distance and following it allowed me to adjust rates, and if desired, I could have moved the focus point for desired composition (which I often do with birds in flight, or animals running, playing, and fighting).
If you wander around the subject while tracking, the autofocus systems must compensate and move the focus to that which comes within the focus sensor, and if you fall off the subject, the focus will be thrown off and will likely lock onto something in the background. Some cameras can not recover from such drastic loss of focus very quickly, with the loss of the best images. The higher end cameras, with their faster response, can recover from such errors quickly. If you use multiple autofocus points, you risk the possibility that one autofocus point will lock onto the background, losing your subject.
Normally, I would not use this strategy of near continuous framing in photographing action such as the eagle. I was taking images to illustrate the longer term tracking of action. I would normally not take so many images early in the sequence when the bird is far away. I would track it as shown here, with my finger half pressed on the shutter button. However, once I saw its flight path, I would wait and frame more images when it was close or had a better background, or was doing something more interesting, as in some of the eagle images, linked below in my Eagle Gallery.
Another lesson, was not shown here. A friend was also photographing close by, perhaps 6 yards away (~6 meters). The bird was flying low enough that from his view, the bird passed on the other side of me, and my momentary appearance in his field of view caused his autofocus tracking to lose lock on the bird, losing some close images. So keep a good distance between you and other photographers in case of low flying subjects.
More birds in flight images can be viewed in my Birds in Flight Gallery.
Additional Examples
Additional Reading
Using multiple AF points in the EOS-1D X and 5D Mark III "http://www.learn.usa.canon.com/resources/articles/2012/5d3_multiple_af_points.shtml This article has good information for other Canon cameras too.
The Action Photography Series:
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http://www.clarkvision.com/articles/tracking.action.with.autofocus
First Published September 27, 2008
Last updated March 8, 2016.