Hello.

Can somebody tells me what is black balance and when it is usefull ?
How it works and what it is for ?

Thanks.

They made an entire movie about black balance, good watch. Invictus (2009) (http://www.imdb.com/title/tt1057500/) :-p

Black balance is roughly re-setting zero luminance. Since you want your whites to be white, you want you blacks to be black.

How often it is needed depends a lot on the camera you're using. I believe that some Phantom HD cameras have to be black balanced between EVERY time you take a shot. Do a search through DVInfo or google to find more info & to see what people think about black balancing as a whole, there isn't going to be anything special w/ a S270 black balancing.

Also see here: Black balance - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Black_balance)