Saving Money On an External Flash for your DSLR
Save money (lots) by NOT buying a name brand smart flash for your camera.
Bottom line - Expert photographers use manual settings on their cameras and their strobes to take photos. It is the newbies, occasional shooters who need the auto settings (see exceptions) - and the auto settings that cost so much on the external flash units for Canon and Nikon Cameras. A "smart" flash from Nikon could cost more than $600 while a "not smart" third party flash should cost $40 or less.
"not smart" means that you tell it how powerful it should be when the shutter is released - and then it gives you the light you set when you click. A "smart" flash takes into account the surrounding light and the aperture set in the camera in order to determine the power of the flash delivered when the shutter is clicked. "Smart" flashes also have a manual mode.
Why do you need an external strobe unit? Don't you already have a flash built into the body of the dslr??
First - the strobe built into your camera is pretty weak. Second, it is immobile. Third, it is only a single point of light.
With a dedicated power source (generally AA batteries) an external strobe has more power. The strobe head can be rotated and pointed in almost any direction. By being removed from the lens about 4 inches, it is often enough to eliminate red eye in photos of people. And, by being movable, the photographer is able to control shadowing on the subject.
A further benefit is most of these strobes come with a 'built in slave', meaning that the light from one flash unit can trigger the flash of another flash unit. That means that for less than 25% of the price of a "smart" unit, you can afford 3 or 4 of the "not smart" units and control them with your built in flash. This gives the photographer a great deal of creative flexibility and the ability to light up an area far away from the camera - wirelessly.
for more on the use of an off camera flash, search strobist with your search engine.
exceptions - there are certain situations where the brain of the flash computer is really helpful to adapt to quickly changing lighting situations and from a practical standpoint, manual settings may not be able to keep up with the changes without missing the shot. An example is weddings where the venue moves from well lit to poorly lit places or in and outdoors, or in and out of shadow situations.
But, most shots are taken in a venue where lighting doesn't change and hundreds of shots are taken in virtually the same setups, same distances, etc. Here the camera can (and probably should) be set to manual settings and the flash also set to manual power. In fact, by using automatic settings, there are many processes that have to work perfectly in order for the proper exposure to be taken. These processes take computing power and an instant of time - which, depending on the computing power of your camera, could cost you that shot.
But, if you are taking wedding photos and faced with varied lighting situations, hopefully you can afford good lighting tools.