The Beamer is designed to be used with lenses of 300mm or longer focal lengths. There are also models designed to fit the various brands and sizes of flash units. My Beamer is designed for use with Canon's 580EX II Speedlite.
Here is a shot of the Beamer affixed to my 50D with the 580EX II and 300mm lens:
A few weeks ago I was trying to find out how close I could get to an Eastern Chipmunk with the outfit shown above, without the flash. I could get close to the minimum focusing distance of the lens but in the lighting under a tree canopy I had to shoot wide open and at a higher ISO in order to keep shutter speeds high enough to get a sharp image. And a lot of the shots were fuzzy due to camera and/or chipmunk movement. Here is an example of the results:
Canon EOS 50D, EF 300mm f/4L IS USM, f/4, 1/90 sec., ISO 400 |
Yesterday, with the flash and extender added to the setup, I was able to use a lower ISO and stop down to f/8 for greater depth of field. I was not as close, which also helps with getting more of the subject in focus. None of the chipmunk photos are cropped. Here are two examples:
Canon EOS 50D, EF 300mm f/4L IS USM, f/8, 1/60 sec., ISO 100 |
Canon EOS 50D, EF 300mm f/4L IS USM, f/8, 1/60 sec., ISO 100 |
For another illustration of the difference the flash extender makes, I shot some hosta about 25 feet from the camera location first without and then with flash. Here are the results:
Canon EOS 50D, EF 300mm f/4L IS USM, f/4, 1/10 sec., ISO 100 |
Canon EOS 50D, EF 300mm f/4L IS USM, f/4, 1/60 sec., ISO 100 |
One thing the flash does is even out the light so that background highlights are not blown out as they can be when the camera is metering a darker area.
You can shop for your own Better Beamer flash extender at Adorama here.