In tips articles # 16 we discussed using flash as a means to improve your bird photographs. This month we will discuss an item that will enhance your flash photography.

Many flashes come with a "zoom head". Basically this is a lens-like device in front of the flash tube that moves in order to narrow or widen the angle that the flash will illuminate. For example, a typical flash may have a zoom head that will adjust the flash angle coverage to match focal lengths from 24 mm to 105mm. The reason for this feature is to prevent lighting areas outside the area covered by the lens. By preventing this "waste lighting", your flash's range is extended.

To understand the impact of narrowing the flash coverage angle, we must look at the flashes "guide number". This number tells us how far a flash can illuminate for a given aperture and zoom setting. For example, consider the following table for the Canon 540 flash using 100 ISO film.

Typically in bird photography we need to use focal lengths in the range of 400mm and beyond. If our flash coverage is ~ 20 degrees when the flash is at its maximum zoom position, and our 400mm lens only sees 5 degrees, then a lot of flash energy is being wasted lighting areas outside the lens coverage area.

To solve this problem a "Tele flash extender" can be used. It is simply an accessory lens that is placed in front of the flash and narrows the beam to approximately the area covered by a 300mm lens.

So what exactly are the advantages to using such a device? First, by narrowing the beam, the effective guide number of the flash is increased. This means that the flash, at a given output will travel a greater distance and thus will need less power to light its original maximum distance. From our example above, the original maximum distance was ~10meters at f5.6. If we double the G.N., for the same energy, we can then shoot 20meters at f5.6(or 10meters at f5.6 with the flash not working as hard).

Now consider the impact of our flash not having to work as hard. The same flash discussed above will give about 100 full power flashes and take as long as 13 seconds to recharge with a new set of batteries. If we use the extender, we will increase the amount of flashes per set of batteries and decrease the recycle time between flashes.

There are a few models of telephoto flash extenders on the market, and can be seen at LL Rue (http://www.rue.com/ruecat.html) and Kirk Enterprises (http://www.kirkphoto.com/kirknews.html). Most models advertise up to a 3-stop increase in flash power (essentially tripling the G.N.), but a 2-stop improvement is a more realistic rating. The best model in our opinion is the "Flash Extender". It can be folded flat and is very secure when attached to your flash. Another model is the "Project-A-Flash". While effective, it is basically a plastic tube that is held in place with Velcro. It is not as secure and is much more bulky and prone to misalignments than the "Flash Extender" model. In summary, the use of a teleflash system will decrease battery consumption and recycle times and allow you to extend the useful range over which your flash can work. Keep in mind that due to narrowing the flash coverage; proper alignment of the device is essential to ensure the lens coverage area is completely lit. As well as concentrating the flash's energy, it will do the same with the sun's. Just like a magnifying glass on a sunny day, you can literally start a fire(or melt your camera gear) if the angle of the sun is right.

Here we see the four components of the "Flash Extender" model. The Fresnel lens on the right hand side is common to all tele-flash systems and serves to narrow the beam. The two side panels are held in place by the elastic strap on the left side. This model can be folded flat for ease in carrying.

This photo shows the unit in place on a flash. The elastic strap holds the side panels firmly in place.