Beginner in the digital flash world question

As I understood until now (and correct me if I wrong) when I using the internal flash of my digital camera, Its shoot a pre flash and according to the result the camera calculate the amount of time for the second shoot of the flash and stop it when the subject got enough light.

Now, when I use an external slave strobe, how is the process? The slave start to shoot when the internal flash start, but how it know when to stop?

Go to Ikelite's web site. Under digital strobes or cameras they have a detailed explantion of how the strobes work with digital cameras.

Good explanations in Ike site.

- Is the Ike strobes with the 'Wireless TTL Slave Sensors' are really the only solution to use TTL in digital U/W cameras.

- Is there someone here that use this Ike setting with Canon S30/40?

For TTL I believe that only the Ike sensor can do it. You can shoot manual with Sea and Sea's digital strobe with the fiber optic cable which I believe can be adapted to any camera with an internal strobe.

Ike makes a tray system for use with their system with just about any camera. That is also shown on their web site.