Terns are fast-moving flying machines. They can change direction in a heartbeat, with no warning. Trying to photograph these beautiful and delicate hunters can be quite challenging.
When photographing birds in flight, it is important to have your camera set properly. A high ISO of at least 800 on a sunny day and much higher, perhaps 1600 or 3200 on a cloudy day, is recommended. A high ISO will allow you to use both a fast shutter speed and a small aperture for good depth of field. It will also mean that your images will show noise (similar to film grain in the old days), so some noise reduction software is helpful. I use the noise reduction feature in Lightroom 5.
A shutter speed of at least 1/1000 sec for moving birds, and an aperture of at least f/11 or smaller will give you the best chances of freezing motion and keeping most parts of the bird sharp. But what is the best way to focus and keep things in focus as the birds quickly change position?
For Canon shooters, use AI Servo. Nikon shooters use Continuous. As mentioned in a recent blog, setting your camera for Back Button Focus is an important first step toward having full control over focus, regardless of what subjects you shoot. If you have not read that blog, check it out at http://awakethelight.blogspot.com/2014/08/back-button-focus.html
But back to AI Servo / Continuous, this control allows you to track a moving subject and keep it in focus as it moves. Depress the focus button and hold it down as you follow the movements of the subject. The camera's focusing mechanism will continually focus on the subject, sensing the change in distances between the moving subject and the camera. It's a little bit of magic.
While it is not foolproof all the time, it is quite good and generally is much faster and more accurate than attempting to manually focus on a fast flying bird. Your best chances of success are to combine this focusing method with setting your viewfinder to show only ONE focus point rather than the several focus points that most cameras are set up for. I set mine for only the center rectangle viewable in the viewfinder. I keep that centered on the bird's head as much as possible, guaranteeing good focus of the head and eyes. Then I crop later as needed if I don't want the bird to be dead center.
A question was asked about whether to keep your camera always set to AI Servo / Continuous regardless of whether your subject is moving or not. Some recommend that approach, rightly pointing out that even set that way, when you remove your finger from the focus button, the focus locks in and will not change until you press the focus button again. I have experimented with that for the past year or two. My conclusion, based on what works best for me, is to NOT leave the camera set to AI Servo / Continuous all the time. I found that occasionally I was absentmindedly keeping my thumb on the focus button at times when I intended to lock in the focus and be done. In addition to using AI Servo for tracking birds in flight and fast moving wildlife, I use it for macro with fairly good success, especially when it is breezy and flowers are blowing a bit. But for scenics, still lifes, and other non-moving subjects, I generally use One Shot.
TECHNICAL DATA
Shutter Speed 1/2000 sec. Aperture f/18. ISO 800. Lens: Canon 200-400mm f/4 with built-in 1.4 extender plus external 1.4 extender for an effective focal length of 784mm. Camera: Canon 5D Mark III. Gitzo tripod with Really Right Stuff ballhead and Wimberley Sidekick.
TODAY'S QUOTE: "If you were born without wings, do nothing to prevent them from growing." --Coco Chanel
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