7.9 Flash Extenders

In bird photography, the primary purpose of the flash (if and when it’s used) is in most cases to illuminate the bird, not the entire scene.  Judicious manipulation of the flash ratio typically provides for adequate background illumination via ambient light, so there’s usually little need for illuminating the background via flash.  Unfortunately, most flash units are designed to provide uniform illumination over the whole frame, and they do this by spreading their light out over a wide angle.  For our purposes, that’s highly wasteful: significant quantities of light are being wasted on parts of the scene that we typically don’t care about (very much).  Although most dedicated DSLR flash units have a “zoom” control that allows you to vary the width of the emitted beam of light (via a sliding parabolic reflector inside the flash head), it’s typically not flexible enough to allow you to focus the light into a narrow beam that would correspond to, say, a finch at 25 feet.  This is where the flash extender comes in.



     Although flash extenders are popularly thought to increase the “power” of the emitted light by making it brighter (thereby allowing it to travel further), what they really do is redirect the emitted light into a narrower beam (or cone) than that originally emitted by the flash head.  They do this using a fresnel lens, which works just like any other lens—by redirecting and focusing light rays.  Thus, the light rays that would have been wasted on the background are instead redirected (and concentrated) onto the subject. 
    Fresnel extenders are very cheap (around $30 US for a small one) and can be extremely effective; they’re also easy to build yourself, as we’ll see shortly.  Not only do flash extenders allow for more intense illumination of a subject at a fixed distance, but for subjects that are close they also allow you to conserve battery power by using lower flash power levels to achieve the same amount of subject illumination.  Given the insatiable thirst of flash units for battery juice, this latter advantage is by no means a trivial one.
    The most popular flash extender for bird photography is, by far, the celebrated Better Beamer (pictured above) by Walt Anderson.  I recently had the pleasure of shooting with Walt at Crane Creek (now called Magee Marsh) in Ohio—a famous hotspot for warblers and warbler photographers in spring.  Of the photographers using flash at Magee Marsh this past spring, nearly all of them were using the Better Beamer.  I’ve personally bought three of them.  However, I now use a larger and more powerful beamer that I constructed from readily-available items from the local art supply store—for about $20 (US).


A “monster beamer” like the one shown above can emit a fairly powerful beam of light (though not powerful enough, as some have suggested, to cause intervening vegetation to wither and die).  The great blue heron (Ardea herodias) shown below was photographed at a distance of roughly 200 feet (as indicated by my len’s distance readout) in predawn lighting.  The image on the left was taken with no flash, while the image on the right was taken with flash.  Even at 200 feet, the flash (with monster extender) was able to light up the entire bird and its perch, revealing far more detail than what the non-flash exposure provided. 


Building a monster beamer like this is simple and inexpensive.  The parts are obtained from local stores, including WalMart, Barnes and Noble (for the fresnel), and Michael’s (art supply).  Plans for building such a device are given in section 4.3.2.* 
    There are several important things to keep in mind when using a flash extender.  The first is that the use of a flash extender can cause irreparable damage to your equipment, and possibly even personal injury or death.  That's worth repeating:

The following story was related to me personally by a very reliable source.  A fellow who had been photographing birds outside his window in the early morning left for work, leaving the tripod-mounted camera rig (with flash and fresnel extender attached) still pointing out the window.  Because the window was facing the sun for a significant portion of the day, the sunlight was magnified by the fresnel, causing heat to build up in the flash unit.  When he returned from work that evening, he found that his flash unit had been transformed into a molten mass of plastic—completely melted by the concentrated sunlight.  Although the flash unit had been totally destroyed, the owner was just thankful that a house fire hadn’t been started in the process.
    I’ve personally had two flash units become partially melted by small fresnel extenders, while out in the field photographing birds.  In both cases, the damage was entirely inconsequential, since the melting was limited to the external plastic housing of the flash (you may have noticed the duct tape covering part of the flash unit in Figure 7.3.1 in section 7.3).  Nevertheless, it’s worth stressing here that if you use a flash extender (of any brand, or even home-made), be careful at all times, especially with tripod-mounted rigs, to ensure that your camera isn’t left pointing toward the sun.  Damage can occur when you leave your tripod-mounted rig for several minutes to talk with passers-by, or possibly even when sitting in traffic with your gear on the front seat of your car. 
    Another potential problem with the use of flash extenders is that they can, over time, cause your flash head to “slouch”.  This isn’t necessarily true of all flash extenders.  For those that are fully supported by the flash head itself, if they’re mounted far out on the head their weight can cause the head to point progressively lower over time, resulting in noticeable differences in illumination levels between upper and lower portions of a bird or scene.  If you use the Better Beamer, the recommended positioning of the extender (fully back against the vertical part of the flash head) should prevent this problem, though many photographers fail to read the instructions and position the extender out at the very end of the flash head, where it exerts the greatest torque.
    The problem of partial illumination of the bird or scene can occur even without the “slouching” problem described above.  For extremely close subjects, the use of a flash extender can result in vignetting—i.e., dark image corners around a bright center.  When working with close subjects I always remove my flash extender to eliminate this problem. 
    Finally, it’s worth briefly addressing the “zoom” setting that’s available on many dedicated flash units.  This setting is typically given in millimeters and represents the angle of view of a lens with the given focal length.  For example, a flash zoom setting of 50mm should result in a cone of light sufficient to illuminate the entire visual field as seen through a 50mm lens.  The flash units I’ve used offer zoom ranges from about 28mm to 105mm—far smaller than the focal lengths used in typical bird photography.  When using a commercial flash extender, consult the documentation of the product to determine the recommended zoom setting for your flash.  For home-made extenders, the optimal zoom setting will depend on the specifics of your design, though my experience (and that of those I’ve talked to) suggests that different zoom settings are often indistinguishable in the field.

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* I’m deeply indebted to several local photographers from Conowingo Dam in Baltimore, MD for the idea of building the large extender—particularly Andy J., who loaned me his home-made extender during my trip to the dam in 2008.  My deepest thanks go to Andy for his many, highly useful suggestions that have substantially improved the quality of my photography.  Thanks, Andy!!