Weight, rigidity and the feel of the head vary with the make and model, and as with tripods, there's a trade-off between a head's size and weight and how much gear the head will securely support. Usually, the heavier the head, the more rigid it will be, making it easier to have the head stay put without allowing the camera to shift positions.
The classic tripod head, the pan-tilt (three-way) head provides separate controls for panning left and right, tilting up and down, and rotating your camera for vertical compositions. The beauty of this arrangement is the precise control over individual motions. If you've already tweaked your horizon, for example, and it's now perfectly level, you won't adversely affect the level if you pan a little to the right. In situations where precise composition is important, the three-way head
allows you to concentrate on one axis of movement at a time. Unlike some other head designs, three-way heads offer their full range of movement regardless of whether you're set up for a horizontal or a vertical composition.
The deliberate nature of three-way heads also is a drawback in some cases. It's slower for quick setups than ballheads, which lock with a single knob. You'll also need to properly level your tripod for the head to work efficiently. (If you don't, you'll see your horizon rotate in the viewfinder as you pan.) Three-way heads aren't very good for following action, so if you're into super-telephoto shots of birds in flight, a three-way head may not be your best choice.
The best thing about ballheads is that you can loosen one knob and the head will move in all directions. The worst thing about ballheads is that (you guessed it) you can loosen one knob and the head will move in all directions. More seriously, ballheads offer access to pan, tilt and rotate simultaneously, so camera positioning on the tripod is much more like the motions you'd use when hand-holding the camera than with a three-way head. A second, and no less significant, advantage is that unless you're shooting a panorama, there's much less need to level the tripod legs and center column, as the ballhead is free to move largely independently of the tripod.
The downside of a ballhead is that loosening the ball to move in one direction may allow unwanted movement in others; that is, after you've taken care to level your horizon, you may have to level it again after tilting or panning.
A ballhead's range of motion doesn't allow vertical shots unless you align the ball's neck with a slot cut into the side of the head. (A number of ballheads now offer more than one slot, simplifying things somewhat.) Some photographers prefer to use an L-bracket instead of working their ballhead vertically. The bracket allows the camera to be quickly attached to the tripod head in either a horizontal or vertical position.
Offset ballheads allow a greater range of movement than either a pan-tilt or traditional ballhead. When used conventionally, the head tilts forward and back through an unusually wide arc while providing rotation for vertical shots like a normal pan-tilt head. Similar to a ballhead, though, tilt, rotation and ball movement lock and unlock with one knob.
The head's ball has the ability to swing the camera platform through a complete circle. Using the ball in combination with the traditional three-way movements opens up possibilities unmatched by other heads. (A great trick is swinging the platform 180 degrees to cantilever your camera out over the railings at overlooks or on bridges, but be aware of the change in balance with the head in that position.) You'll likely find that an offset ballhead offers a lot of flexibility, but its unusual design will take a little getting used to.
Many heads feature a quick-release system so that you can attach your camera in a snap. Quick release frees you from the often vexing task of screwing a camera directly onto a tripod head, greatly reducing both the time taken and the risk of dropping expensive cameras and lenses. Well-made quick-release systems are a huge benefit. If the head you otherwise love doesn't have one, high-quality, third-party adapters are available from a number of manufacturers.
Gimbal heads are designed especially for large, heavy telephoto lenses with built-in tripod mounts. The head supports your camera and lens firmly, but allows you to aim at will, without cumbersome locking mechanisms. The head's secret is positioning the lens and camera so that the center of weight is right at the head's pivot points. That way, the whole system stays relatively balanced regardless of where you point it, and requires very little tension to maintain image sharpness or camera position.
The head's design affords a nearly unrestricted range of pans and tilts, with rotation supplied by the lens mount collar. If your lens doesn't have a rotating collar, you'll need an L-bracket.
Fluid heads are designed for motion picture and video work, but for still photographers with long lenses, the ultra-smooth pan and tilt movements of fluid heads have advantages similar to those of gimbal heads. Like the gimbals, fluid heads also accommodate a wider range of tilt movement than most three-way heads. Fluid heads provide variable tensioning to counteract the weight of your big glass; very high-end models offer counterbalancing, too.
Although they resemble three-way heads, fluid heads don't offer rotation for vertical shots. As with gimbal heads, that's no problem for users of telephotos with rotating collars, but it's a disadvantage to photographers who mount their cameras directly on the tripod head.
Giottos (HP Marketing Corp.)
Gitzo (Bogen Imaging)
Manfrotto (Bogen Imaging)
Slik (THK Photo)
Velbon (ToCAD America)