what does the term TTL stand for?

i never heard of TTL till a few weeks bk and just wonderd what it

actualy is and what it is used for? thanks alot

TTL="through the lens". You see it especially applied to a camera that meters the light from a flash through the lens, and turns the flash off when enough light has reached the film. Many cameras (like mine) meter ambient light through the lens, but can't meter a flash through the lens.

If you're shooting normal subjects (ie, people in a room), it may not matter which you have. If you're shooting macro subjects, or shooting through filters, it would help a lot. The alternative is guesswork, trial-and-error, or calculating the required settings.

To add what Stephen said. Some cameras determine the flash duration twice, once for the intial exposure reading, and a second time off the film. The second reading is what will turn the flash off if you are using a one of the program mode(s) with the camera. You can tell if your camera has the off-the-film sensor by looking through the back with the shutter open. Off to one side you will see a small light sensor pointed at the shutter/film back. It's reading an area off the film for an average exposure to prevent over-exposure from the flash. All this can be manually controlled through the camera or flash if you want by setting the flash in manual mode, where some flashes have intensity control, and the camera in manual mode. Some cameras will automatically set the shutter to a pre-selected speed if you forget to set it correctly, but it won't automatically correct the aperture or flash unit. That you control, mistakes and all.

Good luck.