While most camera accessories may be considered mere conveniences, there’s one that I consider absolutely essential for truly serious bird photography, and that’s the external flash unit.  There are three separate reasons for this, and it’s worth enumerating them right at the outset.  The first (and most obvious) is that birds are very often found in shady environments (such as within a forest), where there may be insufficient ambient light to obtain an image that is sharp, bright, and not overly noisy.  When shooting in dim environments (or on very overcast days), you’ll often find that in order to obtain a reasonable exposure, you need to either use a very low shutter speed (which can lead to blurry images if the bird is moving) or use a very high ISO setting (which can lead to large amounts of pixel noise).  Properly applied flash can, very often, substantially mitigate these problems.

    A second reason to use external flash is that for birds not in direct sunlight, the use of flash can result in more vivid colors, as illustrated by the figure above.  The bird on the left was illuminated with flash, while the bird on the right was not.  As you can see, both the bird and the leaves and branches in the background have more vivid colors.  Part of the reason is that the light emitted by most flash units is set at a color temperature which mimics direct mid-day sunlight, whereas the ambient light which illuminates a subject in shade has different color characteristics.  While it is possible to adjust the color temperature in software (or even via the white balance setting in your camera), the use of higher ISO to increase image brightness still results in less color information (recall from section 2.5 that higher ISO settings don’t actually force the collection of more light; rather, they artificially amplify the signal and noise coming from the photosites), so that color adjustments in software often result in unpleasant artifacts in the image, such as regions that appear too saturated.  In general, it’s best to get the lighting correct in the field, rather than trying to patch up the image later via digital manipulation.
    The third, and far less well-known (among novices), advantage of flash when shooting birds is the effect it can have in bringing out microscopic features, such as the minute structure in the surface of feathers.  The image below gives an example of this.

Unlike ambient light, flash light comes from just one direction: from the location of your camera (unless you’re using a remote flash, which we won’t consider here).  If you think about what happens to the rays of light coming from an external flash unit, you can imagine that these rays strike parts of the bird and then reflect off the bird in some direction.  Those rays that reflect back at exactly the proper angle will be collected by your camera’s imaging sensor, while the rest will not.  Since the angle of reflection is determined by the relative angle of the feature of the bird that has been struck by that ray of light, the camera’s sensor will register more light (far more, in many cases) from those microstructures in the bird that happen to be almost perfectly parallel to the plane of the imaging sensor.  This is illustrated in the figure below.


    Each ray of light coming from your flash unit is represented in the figure above by a vector—i.e., a straight line with an arrowhead indicating direction.  The black contour at the bottom of the image represents some microscopic surface on your subject—perhaps the microscopic surface of a feather, for example.  Those surfaces which are perfectly parallel to the imaging sensor (which is not shown in the image, but you can imagine it off beyond the top of the figure) are shown to reflect their incident flash vectors (drawn in red) back in the same direction whence they came—back toward the camera.  Flash light striking non-parallel surfaces (shown as blue vectors in the figure above) reflect at odd angles which mostly don’t direct them back toward the camera, so they’re effectively lost. 
    The result is that the imaging sensor in the camera receives a much higher intensity of light from the parallel microstructures in the bird’s plumage (and other features), resulting in enhanced contrast at the microscopic level—what I call micro-contrast.  In this way, the use of flash can produce substantially more detail in the resulting image than would otherwise be possible, and this isn’t simply due to a brighter image: it’s due to the use of a strong unidirectional light source.  This effect isn’t as well known outside of bird photography, because most other subjects either don’t have the same degree of microscopic detail as do birds, or if they do have such detail it’s typically not aesthetically pleasing (e.g., microscopic imperfections in human skin).
    One disadvatage of flash, both for people and for birds, is that it very often results in artifacts appearing the subject’s eyes.  In humans, this is known as red-eye.  In birds, it can take the form of red-eye (which typically results from reflections off of blood vessels in the eye) or steel-eye (which results from reflections off of the highly reflective surfaces at the back of the eyeball—which presumably are an evolutionary adaptation that aids in increased light collection in dim environments).  The figure below shows an example of red-eye in birds.  Steel-eye, which typically shows up as a bluish or whitish reflection (rather than reddish) seems to be more common.

Despite the problem of red-eye and steel-eye, I think the potential advantages of the use of flash for bird photography far outweigh the disadvantages.  As we’ll describe in Chapter 11, elimination of red/steel eye in postprocessing becomes relatively easy with practice, and as mentioned below, some steps can be taken to prevent its occurrence in the first place.


4.3.1 Models and Power

Once you’ve acknowledged that the use of flash (at least some of the time) is necessary or at least useful for bird photography, the next step is to realize that the tiny flash unit built into your camera isn’t powerful enough for general bird photography scenarios—i.e., situations other than the one in which you’re sitting at a window, three feet from a bird feeder.  As the figure below should suggest, internal (i.e., built-in) flash simply can’t compete with the power output of a dedicated, self-powered flash unit.


Modern flash units are rated in terms of guide numbers.  The guide number indicates the overall power output of the flash unit.  Understanding the theory behind guide numbers is essentially useless when shopping for a flash unit, since for bird photography you only need to know one thing: the more powerful the flash, the better.  For portrait and wedding photographers, a unit with only moderate power output may be more than sufficient, but for really serious bird photographers, no amount of flash power is ever truly enough; there’s always a bird that’s just too far away for the flash unit to effectively illuminate it.  The bright side (no pun intended) of this situation is that choosing a flash unit thus reduces to a simple financial question: what is the most powerful flash unit you can afford?  Although I do very strongly recommend buying the most powerful flash you can afford, there are ways (as we describe below) to increase the effective output of a given flash unit, by restricting and refocusing the flash’s emitted light.


4.3.2 Fresnel Extenders

One of the most notable developments in bird photography in recent years has been the widespread availability of the fresnel extender.  I recently had the pleasure to meet the man who is largely responsible for making this technology available, affordably, to masses of bird photographers.  Walt Anderson’s now-famous Better Beamer flash extender utilizes a simple and highly economical method for concentrating flash output into a smaller area than would normally be possible with the naked flash head.  The figure below shows the Better Beamer (two of them, in fact) in action in the field.



As you can see, the beamer is a simple device which attaches to the front of your external flash unit, via velcro straps.  The above photo was taken during a bird migration festival at a migrant trap in Ohio.  Though you can see only two lenses in this figure, had I used a wider-angle lens to snap this photo you’d see a line of 15 or 20 tripod-mounted lens, nearly all of them surmounted by a fresnel-extended flash unit.  The extenders shown above are very affordable—I got mine for about $35.
    A fresnel extender is simply a lens.  Like any lens, the extender works by refraction—that is, by focusing light to a point (or at least to a smaller area than would otherwise naturally occur).  The light emitted from a flash unit tends to spread out over a wide area, which for most types of photography is a good thing: the goal is typically to illuminate an entire scene.  But with a super-telephoto lens in the 400mm-800mm range, the field of view is so restricted that much of the illuminated scene isn’t even visible in-frame.  An enormous amount of flash light is wasted on parts of the scene which won’t even appear in the photo.  A fresnel extender simply takes that wide cone of light and narrows it, so that it is concentrated in the part of the scene which does fit in-frame.  As a result, the amount of light striking the bird can sometimes be enormously greater than without the fresnel. 
    There are two main advantages to this.  For birds that are at relatively large distances from the camera, the use of a fresnel extender can make the difference between illuminating the bird and not illuminating the bird.  I once lit up a heron at 200 feet (!) in pre-dawn lighting, using a home-made “mega-beamer” (the heron is shown just below, while the beamer is shown in the figure that follows).  Without the extender, the flash would have had no discernible effect on the illumination of the bird. 


The other advantage of using a fresnel extender is that for birds at closer ranges, you can turn down the power output of your flash unit, thereby conserving your batteries.  It’s a well-established fact that flash units can eat batteries even faster than the Cookie Monster can eat Oreos.