Sunday, September 20, 2009

Prime Lenses: A tutorial for the rest of us...

What is a "prime" lens?

A prime lens is what all of the old masters started with. They let in a freak'n ton of light and are extremely sharp but with the trade off of not being able to zoom the lens. Want to "zoom" in closer? You have two choices, walk closer, or use a prime lens that has more of a telephoto focal length. BTW, "telephoto focal length" is nerd-speak for a lens that sees closer to the action rather than farther away (wide-angle).

Here is how the numbers on a prime lens work: a 50mm f/1.8 lens means that the focal length (what the lens "sees") is 50mm. This is about the same focal length that you would see if you didn't have any peripheral vision. Try holding your hands flat on the sides of your face like horse blinders to get an idea. Now get a friend to hold their hands flat on the top and bottom of your hands forming a box. Now look in the mirror. Don't you look silly.... :-)

The "f/1.8" portion is a measurement of how much light the lens will let in. It's really just a ratio of the focal length of the lens divided by the diameter of the opening in the lens. The wider the opening is in the lens then the more light that will be let in to the camera. A lens with an f-stop of f/1.4 will let in from 8 to 16 times as much light as the typical kit lens
that came with your camera.

A side affect of having a wide opening (lower f/number) is that you will get a more shallow depth of field. What in the heck is depth of field (DOF for short)? DOF is how much of the image is in focus. Ever seen a picture where part of the picture was in focus and the rest was blurry? That means that there is a Shallow DOF. If a picture has a Wide DOF then that means that more of the picture, is in focus.

Portrait photographers and photographers who work in low light settings love prime lenses, they are relatively inexpensive compared to most pro lenses, they make great portraits, and they are generally very small and Portable.