I was wondering about what something is that I see most big time directors using...its this medium sized scope...looks like a lens...I always see the director looking through it...I was wondering what it is...what its used for...and where do you get one if its affordable.
Those are for previzualization. The director can look through it, to get a feel for framing his shots. I am not really familiar with them, but there are companies that just make those. I have a very strong feeling (though I'm not positive) that they are very expensive. You really don't need one. YOu can just look through your own camera lense and get a feel. Their cameras are a lot bigger though, and it is harder to frame for shots with a big 35mm camera that can only be moved smoothly via track, dolly, crane, steadicam.
The technical term for the scope you are referring to is called a viewfinder, typically used between directors and cinematographers to compose a shot.
As Lazlo said, you can look through the viewfinder that's available on the camera to accomplish the composition of a shot.
But, when used on sets that employ larger camera systems, a mobile viewfinder is a necessity. In those circumstances, a viewfinder ensures a greater a level of accuracy in the outcome of the shot, because it allows the director and the DOP to collaborate in the pre-visualization process as they strategically scale the next shot.
Mini viewfinders, found on sites like filmtools.com can cost a few hundred dollars. Where as, the viewfinders that you've seen directors and their DOP's meticulously peer through on set for big budget movies are priced considerably more.