Last month we covered the all important basics and fundamentals of photographing birds in flight. We talked about the significance of starting small with gulls and how practice, and more practice with the best bodies and lenses you can afford will ultimately produce the results you have only dreamt of. Once you have mastered your technique and are ready to move on to smaller, faster birds, its time to learn more about some of the technical options available on modern equipment that, depending on how you use them in various field situations, can have a great effect on your in-flight images.
Which shooting and metering mode works best?
As a general rule, neither Av nor Tv is ideal for flight shooting, although I know photographers that use Tv with some degree of success. Shutter speed is usually more important than aperture for flight shots. For me, lighting varies too much in quality and quantity to get consistent results on days where any clouds are present with either Av or Tv. I prefer to meter for the intended subject manually using either evaluative, partial or incident metering. Knowing the subject will be exposed correctly regardless of sky or other background anomalies eliminates one more variable for me and increases my chances of producing "keeper" images. Your mileage may vary, but at least try shooting in manual mode the next time out - enjoy the total control it gives you. Automatic modes and metering have their place, but flight shooting is not one of them. Think Manual Mode!
One Shot, AI Focus or AI Servo focusing mode?
First, let's take a look at the differences in these three focusing modes. With one shot, when you depress the shutter part way, focus is attained and locked - if you trip the shutter, your image will be made at that focus distance. In one shot mode, if focus cannot be attained, the focus light blinks, and the picture cannot be taken even by depressing the shutter fully. Most cameras have a significant shutter lag, and focus won't be accurate for any moving subject unless it is moving parallel to you. Intermediate cameras such as 10D, 20D have AI focus mode, which is automatically activated when shooting in one shot mode, and the subject moves. It is not as fast or accurate as AI servo. AI (Artificial Intelligence) Servo utilizes predictive AF - you depress the shutter part way, and the camera continually calculates where the subject will be, tracking the subject and focus is constantly adjusted accordingly. Autofocusing and subject tracking continues as long as the subject remains within the Area AF Ellipse. In my opinion, AI servo is much more accurate for flight shooting. There are exceptions, and some highly skilled flight shooters use AI focus successfully by constantly tapping the shutter, tweaking focus and tripping the shutter at the exact moment when the subject is sharp in the viewfinder. I shoot in AI Servo 100% of the time.
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Which sensors to activate?
This of course varies with your camera, brand and its respective options and number of available sensors. I will describe Canon since that is the system I use, but other systems have similar, if not the same options. My EOS-1D Mark II has 45 available AF sensors. For general use, I activate Custom function (C.fn) 13-3 which makes the center AF point and 8 peripheral points selectable. For about 65% or two thirds of the time flight shooting, I use the center AF point only. It is just faster for me, and it's the best way to AF on a bird's eye when that opportunity presents itself, say with large birds. Occasionally, I use C.fn 17 to expand the AF activation area to either 7 or 13 AF points. This is particularly useful with small, fast moving subjects. C. fn 20 allows me to adjust AI servo sensitivity such as keeping AF from being thrown off by an object moving between myself and the subject. If I have an unobstructed background such as blue sky, I will often use all 45 sensors. The "ring of fire" is highly effective and fast to acquire AF, but it will not work well against busy or uneven backgrounds.
Focus delimiter and stop focus button:
Many modern telephoto lenses have focusing limiting capability. By using that feature, we limit the distance the lens travels searching for AF. AF itself does not work any faster, but time to acquire AF is reduced by up to 50%. Another feature present on long teles is the focus stop button. If I press that button focus stops right then. That can be useful in low light or anytime your camera/lens locks on focus but has trouble, for whatever reason, holding focus.
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Other relevant factors:
AF speed is determined by both camera and lens. AF sensor configuration, spacing and sensitivity vary among body brands and models. The same holds true for lenses - some of the fastest lenses have focusing motors built in. The amount of light reaching the sensor configuration affects its speed. That is why a 300mm F2.8 lens will acquire focus faster than a 300mm F4 lens. We all love teleconverters for the added magnification they afford us, but again it's a light level issue - teleconverters cost us from 1-3 stops, and thus affect AF speed and performance.
One final thought... Persistence!
Even after you become a consummate flight shooter and fully understand and use all the technical features described above, there is still no guarantee you will get fantastic images. Having the tools is all too often not quite enough. Persistence will get you there. Note the image of the Scissor-tailed Flycatcher with an insect in its beak. To get that image, I spent about 7 hours over 3 mornings photographing a nesting pair of STFC's. I took over 200 images, and out of them about half were OK technically, but I only kept about a dozen.
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