Why Flash Photography?
For most of the last century, on-camera flash photography was relegated to either a flash bulb that was only one brightness (power) or later in the century to electronic flash that was at first only one power (later versions had switches that allowed for full power, half power, and quarter power).
To give you an idea of how primitive the use of flash was, photographers used to lick the base of the flash bulb just before they put it into the flash bulb socket, in hopes of improving the connection (flash bulbs were notorious for not going off). In the 1960s flash manufacturers started to make electronic flashes with a sensor in them that was designed to measure the light that was reflected back to the camera/flash from the subject. The idea was that when the sensor on the flash received enough light, it would tell the flash to shut off. The flash duration, the length of time the flash is on, can vary from about 1/1,000 of a second to 1/20,000 of a second, well beyond a person's ability to perceive the difference. Just a note: if you actually hear a flash talking to a camera call me; if you hear the camera answer the flash, stop what you're doing and call a doctor.
In the 1980s manufacturers of 35 mm SLR cameras started to introduce cameras and flashes that used TTL (Through The Lens) technology. With the introduction of TTL flashes came the term "dedicated." A camera designed to be used with a dedicated flash has internal sensors capable of reading the amount of light reaching the film. This ensures proper exposure of the film. A dedicated flash can usually be identified by the number of contacts on the bottom of the flash shoe (e.g., Nikon has 4 contacts, Canon has 5 contacts). If you have a flash that has only one contact in the middle of the shoe it is not a dedicated flash.
Most flash photographs look like they were made using a flash. The brightness of the flash overpowers the existing light. The exposure is fine for the people, but the surroundings are dark. Most of the indoor photographs made of you in your life were made with a camera and a flash strong enough to have overpowered the existing light.
The best example I have of this phenomenon is found in wedding photographs. A wedding photographer (during the wedding day) will be in many different kinds of indoor light. The simplest way to cope with the different kinds of light is to use a flash that will be powerful and bright enough to overcome the existing light. As you look at your family's wedding photographs, please notice that the pictures are sharp (the result of using a small aperture) and the light is just right, on the people. Also notice that the surroundings are dark. This technique has been the tried and true method for over 75 years. But the times they are a changing (sorry, I just couldn't resist).
In the 1990s camera and flash design started to get interesting. Nikon Camera, as well as the other camera manufacturers, figured out a way to control the flash by putting a computer chip in the lens that told the camera and flash how far away the lens was focused. The theory is that if the camera and flash know how far away the lens has focused, then they can tell the flash to turn off after the point-of-focus has received enough light, thus ensuring proper exposure at the point-of-focus. WOW.
Many serious photographers avoid using flash. For some, the traditional way of using flash is not artful enough, for others using flash is just too uncertain. The flash's duration (time) is just too short to see what's going on with the light (remember flash times vary from about 1/1,000 of a second to 1/20,000 of a second). The newest equipment has reached a sophistication that older photographers never even dreamed of. It is now possible to balance the light from flash with existing light in such a way that no one can tell a flash was used. You can now use a flash to help correct color, or to fill in a shadow just enough so you don't have to jump through hoops in the darkroom to make a good print. The newest Nikon flash even has a flash preview button.
