7.3 Built-in Versus External Flash

As already mentioned in section 4.3, the built-in flash unit on most cameras can’t compete with dedicated flash units that are attached externally (either directly or indirectly) to the camera body.  The external units tend to have much larger bulbs and can therefore produce stronger pulses of light that are able to illuminate subjects effectively at a greater distance.  Just as longer focal-length lenses are useful for magnifying birds at a distance, a larger flash unit will do a far better job of illuminating birds at a distance.  Many pro camera models don’t even have a built-in flash, because manufacturers know that most pros will opt to use an external unit when they need flash.

Fig. 7.3.1 : Built-in flash (left) versus external flash (right).
The external unit is both larger and far more powerful.
Note the duct tape on the external unit, to protect it from
melting when using a fresnel extender (see section 7.9).

    External flash units aren’t cheap.  I use Canon’s largest model, the 580 EX II, which currently has a street price of about $400 (US); other models can be had for as little as $250 new.  If you use two cameras in the field (one attached to a tripod-mounted large focal-length lens, and another attached to a shorter lens for flight shots), then you’ll ideally want to have a flash unit for each, thereby doubling your cost.  Although you can fairly quickly remove the flash from one camera and attach it to the other camera as you switch from stationary to flight shots in the field, this can become too cumbersome if you’re using an external battery pack (see section 7.4), since you’ll likely have the pack attached to the camera’s strap, or to the tripod. 
    It is possible to use third-party flash units with major-brand camera bodies; Sigma and Metz are two third-party companies that make such units.  Some photographers have found such third-party units to work as well as the major-brand (OEM) models.  However, some of the third-party units cost as much as the OEM units, and while a particular third-party unit may work with your current camera, there’s always the possibility that it may turn out to be incompatible with newer bodies, should you ever upgrade (and most people do eventually upgrade—especially with the never-ending advance of digital technology).
    External flash units not only provide far more power than built-in units, they also typically provide more flexibility in terms of the settings and operation of the flash.  For example, some built-in flashes can’t be used in high-speed sync mode.  Also, some people find the controls on the external flash (i.e., its dials and buttons) easier to use during quick shooting than the equivalent controls for their camera’s built-in flash.  For example, in order to adjust the flash exosure compensation (FEC—see section 7.5) through the camera, you may have to press several buttons on the camera and then turn a dial, whereas on the external unit itself it may be easier to adjust FEC via a simple dial on the flash’s control panel.  On my system I have to press a button and turn a dial in either case (on-body or on-flash), but I find it more convenient to make quick adjustments in the field using the flash’s external controls, since I can do it without taking my eye away from the viewfiner.  One other feature of external units is the ability to change the angle of the flash head.  This is almost never useful for bird photography, but when using your camera for non-bird photos this can be useful for getting a diffuse light pattern on your subject.
    When choosing an external flash unit, there are a lot of features that you can probably ignore altogether.  One that I’ve never used is the capability for wireless control.  Many units can be triggered either by infrared or visible light from other flash units, which is useful if you have multiple flash units that you want to fire simultaneously.  Some photographers will use up to five flash units positioned around a nest or flower (in the case of hummingbirds
see section 7.7) in order to light up the bird from all sides, and this obviously requires a reliable synchronization mechanism, as well as individual tripods or mounts for each of the units.
    Although the capabilities of external flash units far outstrip those of built-in,
pop up units found on consumer-grade and pro-sumer bodies, the use of external flash can be quite a hassle.  Whereas internal units operate off of the camera’s battery, external units require their own batteries—and plenty of them.  For each of my two flash units that I carry into the field I use twelve AA batteries: four in the flash head and eight in an external pack.  The external pack is heavy and needs to be attached somewhere.  I typically attach my pack to the camera’s strap, which makes the camera feel that much heavier when holding it up for flight shots.  I’ve tried hooking the pack onto my photo vest, and this can work quite well, but it can be dangerous if you forget that you’re tethered to your tripod-mounted lens: as soon as you try to walk away from your tripod the cord will begin to pull on your camera and can knock the entire rig over.
    External flash units also get in the way when moving through dense foliage: they get caught on branches, and can snap off, possibly breaking the camera’s hot shoe (where the flash attaches) or the flash itself (or both).  Adding a flash extender (section 7.9) only increases your chances of snagging on branches when traveling through the forest.  The cable for the external battery pack (if you use one) can also catch on branches, or get tangled up with the handles on your tripod head.
    Finally, external flash units can suffer a meltdown, if used for too many consecutive shots at full power; we’ll discuss meltdowns and how to avoid them in section 7.10.  In section 7.9 we’ll also see that the use of external flash extenders (an absolute necessity when using flash for birds at moderate-to-long distances) can damage your expensive flash unit (or even your camera, if it’s made of plastic) by focusing the sun’s rays through the fresnel and melting the outer plastic housing of the unit.