How to Use video camera lens basics: Angle, focal length, DOF
Mike from the SubStream's "Film Lab" has some tips regarding video camera lenses.
In part one, Mike talks about the basics of lenses, starting with focal length and angle of view. It's a lesson on the analog collections of lenses cinematographers use with their cameras. For people who like to point lenses at things, here is the functional knowledge.
A lens collects light, bends it.
Focal length is what they are talking about when they say 10mm or 100mm lens. The focal length of a lens determines its angle of view.
What is angle of view? The number of degrees you can see through. The larger the focal length the narrower the field of view (you see trees). The narrower the focal length the wider the field of view (you see the forest).
In part two, Mike continues his discussion of lenses, focusing (hah!) on the effect of focal length on depth of field.
When you change focal length you change the depth of view.
A wide angle lens or a long lens both can get a filled frame. Short focal length has deep depths of field, meaning things 2 feet are in focus as well as 20 feet away.
Long lenses have a more shallow depth of field. This is good for keeping the object you desire the only thing in focus.