Reaching for Light
I recently bought the Visual Echoes FX4 Flash x-tender to compliment Auto FP high-speed flash with my Nikon SB-800/D200. Because of the Auto FP high-speed function I can now synch at any speed I like, and often I choose 1/500s, a standard for me when shooting wildlife. Ordinary fill flash using TTL metering can produce a good exposure up to 47 feet at 1/250s synch speed. But, that drops dramatically to the 11-14 foot range at the higher speed. Eureka! Regain the distance with a flash extender.
A rude awakening; so far it doesn’t work that way. There are actually pulses of light in this FP function in order to synch with the travel of the focal plane shutter in the camera. That translates to weaker light output. In normal flash mode, called front curtain, there is one brief burst which is altered for proper exposure by duration, not by intensity. So, this may be part of my problem. I am still working on this issue. The Flash x-tender works best for me from a flash bracket. I use the Wimberley F-1. To test the full effect of the x-tender, set the flash to manual mode, and according to its developer, Walt Anderson, at a distance of greater than 25 feet. It will work just as well in TTL mode.
Telephoto shots in low light require a longer flash burst. Nevertheless, all light emitted from a strobe is measured in milliseconds, which is why when flash overrides ambient (incident) light, it does such a great job stopping action, even with a shutter speed of 1/60s. Actually flash at full power is significantly slower than some fraction of full power. So, the farther you are from the subject, the less likely you are to stop the motion of hummingbird wings. (Nikon SB-800 users will find the relative speed in 1/1000s of a second to power settings in the instruction booklet.) When ambient light is the primary source however, the flash acts only to fill shadows or provide a catch light in the eye of the subject. Consequently high shutter speeds are necessary to stop action. Some cameras have a slow speed synch function, which is 1/30s and will allow more ambient light to show in the background for a more natural looking picture. I have not tried it.
So now we have come full circle. The only digital SLR cameras with that 1/500 synch speed of which I am aware are the Nikon D70, D50 and the professional Canon EOS1D. I believe Panasonic has built that feature into its Lumix line, but the construction of that body and the putative slow write speed limit its use for active subjects. It is my understanding that higher flash synch can be achieved with the CCD sensors, but not currently with the CMOS sensors, which is newer technology being employed in professional cameras. While we are on this thread, medium format cameras, in which the leaf shutter is built into the pricey lens, can synch at 1/500 for sure, perhaps higher. I don't remember. In any event, bird photographers often shoot small subjects at telephoto distance, and need speed. Flash synch Nirvana is not yet in sight.
Also, at some point when ambient light drops too low, shoe mounted flash will not deliver sufficiently at high shutter speeds, even with the flash set on 1/1 manual. At that point you may want to try switching back to 1/60s in manual or aperture preferred mode, and let flash overcome what is left of ambient light, giving you a well exposed subject in great detail with a dark background. Or, go with a multiple flash set with the light source closer to the subject to decrease flash duration, and throw light on the background of the scene. With some subjects at feeders, such as the hummingbirds above, I am feeling the pull to try this. However, it will probably require 3 flash units, wirelessly linked on tripods or light stands.
If the subject of outdoor flash photography is of real interest to you, here is a link to Nature Photographers Online Magazine and four articles written by Joe McDonald on the subject of using flash on wildlife. I found them reasonably useful. Find the link to articles, and scroll back to May 2003.
Your comments are welcome.