I saw a video someone shot with a 35mm lens and it had a very shallow DoF. He said he used something called a Canon extension tube. First time hearing about these things, what are the pros/cons of them? Are there any for the FS100 that are any good?

That would be an extension tube for the lens, not the camera. They're usually used for macro work.....IF that's what they were using. Seeing some footage would help.

Lens.Beauty on Vimeo

Here's Aaron Nanto's video where he uses it. Very cool work!

As the subject is moved closer to the camera the lens must be moved further from the sensor to achieve focus. An extension tube increases the lens to sensor distance in order to allow closer focus. For a 1:1 reproduction (object same size on sensor as in real life) the lens to subject distance would be 2x the focal length of the lens. Tubes come in various lengths and can be stacked. For extreme close ups or very long fl lenses they make a bellows that dramatically increases the lens to sensor distance.

A set of three sizes on Ebay goes for as low as $10, if you want a version that has circuits paths to maintain electrical contact with the camera (maybe more important on a DSLR, at least for now) the cost is higher but affordable.

Or, just get a proper macro lens and be done with it.

‪Chops!!‬‏ - YouTube (http://www.youtube.com/watch?v=W9Cqn8HnNn4)

I shot this on my D90 with a 50mm 1.8. I used the shortest tube possible for this, basically just the front and back end. I've been using these as cheap macro converters for years, but you need the expensive versions to get metering.

Duncan

You could also get a used BR2 reversing ring as well. Just turn your lens around and shoot full manual. Kind of a pain to get any sort of lens shading on....but still:

Amazon.com: Nikon BR-2A - Reverse ring Nikon F - 52 mm thread: Camera & Photo