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Consider the image below: enter image description here How would the shot be focused here? Using Auto-focus or manual?
If there was a cluttered background, will auto focus detect the small bird and sharply focus on it?
If manual focusing, how would you continuously focus on a moving bird?

Also in dynamic situations like this, is it easy to manually focus quickly?

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4 Answers

up vote 9 down vote accepted

You will want to use an automatic continuous/servo mode to photograph birds in flight (BIF). Most modern cameras support some kind of servo mode, even entry-level cameras. Using servo mode is only part of the solution to tracking BIF, however. More advanced cameras offer additional AF features, such as multipoint AF Expansion or Zone AF that will use more than one focus point around your key selected point. The use of an AF Expansion/Zone AF mode will improve your tracking ability over the use of a single point. Tracking ability is often dependent on the AF system used, and if you have the option, using a system with more and denser points, particularly those with configurable zones, will improve your ability to track subjects.

Additionally, a denser AF system, such as the newer reticular 51-pt Nikon and 61-pt Canon, offer more points that are more closely spaced together which can greatly assist in subject lock and continuous tracking. Most Canon cameras have a 9-pt AF system that is not reticular, and there is quite a bit of space between each point. The Canon 7D uses a 19-pt AF system that is not reticular, but definitely denser than the standard 9-pt system, and every point is a high precision cross-type point which can identify and lock subjects much more quickly. Canon's 19-pt AF system supports Expansion and Zone AF modes. Canon's newest AF system is their 61-pt AF system with 41 cross-type points in a reticular design. This AF system is currently only found on the 1D X and 5D III bodies, however it is the most advanced AF system available at the current time. It supports full multi-dimensional tracking (frame position, distance, RGB color information), multiple types of zone and expansion AF modes, as well as spot AF (smaller area single-point AF, which can be useful for focusing on very precise locations...say a birds eye). Canon's 61pt system is also the first to offer 5 center double-cross type AF points with ultra high precision for extremely fast focusing.

In Nikon systems, there are 11-pt and 39-pt AF systems in lower-end bodies. The 11-pt systems are roughly similar to Canon 9-pt systems, however their 39-pt system is more of a reticular design. It offers 9 cross-type high precision points around the center. All Nikon AF systems support what they call "3D Tracking", which simply means they use frame position, distance, and color information to help inform the AF system of where the subject is likely to be in the next frame, supporting advanced tracking. To use 3D tracking, you must use all 39 points, which is actually less effective than it may sound (more in a bit). Nikon's latest AF system is their new 51-pt, which is also a reticular design. It supports some semblance of Zone AF, although it only works around the center point. The strength of Nikon's system is multi-point f/8 AF...up to 11 points with a single center cross type and 10 surrounding line sensors. This can be a bonus if you intend to use lenses with teleconverters that reduce the maximum aperture to f/8 (i.e. a 600mm f/4 lens with a 2x TC for 1200mm.)

If you intend to track birds in flight, your main options are going to be multi-point mode (all points) with dynamic subject tracking. This would be all 9, 19, or 61 points in a Canon body, or all 11, 39, or 51 points in a Nikon body. This is often recommended by each brand, however it is not as effective or guaranteed as it sounds. When using every single AF point, the camera...rather than you, decides which points should be in focus. Its not uncommon for an AF system, even an advanced one, to decide it should focus on something other than your subject, suddenly switching subjects without warning. Additional tracking logic can be used when performing multi-point dynamic AF, and when used right, it can be very accurate...but you will always have that potential for instantaneous subject switching hanging over your head...and when it strikes, you can lose that keeper moment.

In the area of configurable AF tracking for birds, I think Canon has the general edge. Their new Zone and Expansion AF modes allow you to select the AF point you wish to be your key point, and configure how many points around that key point can be used to continue tracking if your subject moves beyond the range of your key point. Expansion mode simply selects the four adjacent points, top/bottom/left/right, and marks them active but secondary in "spot AF" mode. If your subject moves away from your selected point and onto one of these four neighboring points, it will continue to track. Zone AF mode is similar, however if will use as many neighboring points as possible, all as full AF points (vs. spot AF points). In the 7D, Zone AF can use up to 9 points at a time, and in the new 61pt AF system you can configure how large the zone is. Tracking birds in flight with Zone and Expansion AF around ANY point is the best way to go, if you have the option. Currently, it is only available on three bodies, the 7D, 5D III, and 1D X.

Nikon offers similar functionality, however I believe it only works around the center point. Nikon's zones extend a strip of line sensors out nearly to the edge of the AF spread range, which helps you continue tracking subjects as they move across the frame. This is a small limitation over the Canon system, but it can still be used effectively. If you have supertelephoto lenses and teleconverters, you can use up to 15 points with lenses that have less than f/8 apertures (such as an f/4 lens with a 1.7x TC), or 11 points with lenses that are f/8 apertures (such as an f/4 lens with a 2x TC or an f/5.6 lens with a 1.4x TC). Some of these points remain cross-type as well, offering high precision, low light, multi-point AF ability, something not currently available on any Canon body.

Finally, you will probably also want to configure your AF system a bit as well. You will want to prioritize AF acquisition and tracking over AF drive and shutter release. This will prevent you from being able to actually start taking pictures until the AF system has a lock on your subject and is able to track. You will also want to support continuous tracking, and avoid shutting off the AF system when it determines the subject has moved beyond the edge of the frame. Finally, you will want to tune the AF system to switch subjects slowly, rather than quickly. A moderate slow setting will be good for most birds, including those with erratic flight. If you are photographing when multiple birds are in flight, using the slowest tracking sensitivity, as that will limit how often the AF system decides to switch from one subject to another when they cross paths in your viewfinder.

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Continuous auto-focus is almost always the right choice, but it's also just the first of many decisions you need to make. (warning: ultimately the answer is going to come down to "know how your gear will react in a given situation" and "practice practice practice").

To successfully get shots like this reliably, you need to learn how your camera functions and how it'll react. Just turning on auto-focus or AI-SERVO (on Canon) isn't enough. Do you pick up a single spot focus point or do you use something that focuses across a range of AF points? Is there clutter in the shot that might confuse the AF? Is the bird going to fly parallel to you or is it coming closer or going away? what's your depth of field?

For a shot like this, I'd set my camera to AI-SERVO, with the auto-focus using the single central spot (on a Canon 7d: spot, single point select) or use an expanded spot focus. The risk is that if you don't keep the bird centered so the AF point is on it, your focus will range and you'll lose focus. In some cases, zone AF works better (but can be a bit slower). Zone AF fails if you have branch clutter, where you can with practice many times pick a focus through the branches. If the bird is stationary, once you get focus, stop AF. Don't turn it on again unless the bird is moving out of your sharp focus range. (to do this, you need to disconnect AF from the shutter button and attach it to another button. That's possible for all modern Canon bodies. I'm sure Nikon can do it as well).

If you can, pre-focus before the bird takes flight. If the bird is flying in a path where focus is going to stay sharp, then don't activate AF again. If you need AF, activate it, but that's one more detail complicating getting the shot...

On a Canon 7d, there are four styles of AF you'll likely use for this kind of shot: single point focus, extended spot focus (which uses four spots around the chosen spot to help lock in AF), range focus (which uses the center region AF points) and full range (which uses all AF points). The wider ranges of AF are more forgiving but more sensitive to clutter in the frame and slower to lock on. Spot is faster to lock on, works better in poor light, but depends entirely on your ability to keep the subject not only in the frame, but within the view of the AF point you've set. That takes practice (and some luck).

I almost never manual focus when shooting birds and wildlife. What you can do (especially when splitting AF to a button off the shutter) is to use AF to lock in focus as needed, and then tweak it manually. Where manual focus makes sense is in a highly cluttered frame where the AF gets confused, and where you have an opportunity to pre-focus so when the bird or animal moves, it moves into the location you planned for. At that point, AF only gets in the way, so you should have it de-activated.

The way to get good at this is practice, by going out and shooting with your gear in each AF style and studying how the camera reacts in various situations. Over time, you'll learn which modes to use and which ones don't work as well for you. Successful bird photography (especially flight photography) also really needs time spent studing the birds and their behavior so you can predict what they'll do and pre-plan a shot for that situation. Does the bird take off parallel to the ground or jump up? Is a take-off flat or more vertical? Does it tend to fly forward, or launch and turn?

If you want to get past "spray and pray", you have to invest the time. The camera can make some of the tasks easier, but it's not a replacement for practice and study. And luck....

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Totally agree with "use AF to initially lock in, then switch to MF to tweak". I've been practicing this with my new hummingbird feeder, with nice results even on my relatively primitive Canon 500D w/ EF-S 55-250. –  khedron Aug 30 '12 at 2:33
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Continuous auto-focus is best in almost all cases. Manual focusing on a small, fast moving object is nearly impossible to achieve with any accuracy.

Speed and accuracy of autofocus will be affected by background clutter, the colouration of the bird in question, the lighting conditions, and the quality of the lens. Auto-focus systems work best where the subject is in clear contrast with its background, so a bright red bird against a green background would probably be focused on relatively easily, for example.

Many cameras have a dynamic focusing mode that will attempt to track a subject across focus points, with varying levels of success, subject to the conditions above. Shooting against a clear sky, as in this shot, is ideal.

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My experience shows that using continuous autofocus (AI Servo for Canon, AF-C for Nikon and Sony, AF.C for Pentax, C-AF for Olympus) with all or a large number of the autofocus points active gives the best results. The area AF systems in high-end Canon and Nikon cameras offer the highest performance currently available when tracking moving subjects, with a large array of points capable of accurately tracking and predicting subject motion and distinguishing between the subject and the background or an obstruction. Using manual focus to track a moving subject, especially when the subject is a small, fast-moving bird, is not going to be easy.

As a Pentax user, I find that AF.C with all 11 AF points works best against a clean background. If the background is more complex, it may be better to use the center 5 points or even a single point.

Red-tailed Hawk in flight
Pentax K-r with Pentax DA L 55-300mm @ 300mm. Tv, 1/400s f/5.8 ISO 160. AF.C, 11 point AF. Red-tailed Hawk in flight

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