Thursday, April 26, 2007

Showing up
(continued from yesterday)
All those settings we talked about yesterday do have a use. First, we need to understand that an exposure of, say, 1/250 @ f-11 is the same as 1/500 @ f-8. "opening" the lens one f-stop doubles the amount of light entering the lens. Cutting the shutter speed by half has exactly the opposite effect, thus balancing the two combinations. In each case, the film or pixels get the same amount of light. But why bother, you ask. Sometimes it is obvious. You use a fast shutter speed to stop or "freeze" action, such as a white water stunt. Other times, you want a slow shutter speed to blur, say, water (see two days ago). Sometimes, however, it is the f-stop that takes priority, and you need a shutter speed to accommodate it.
Say you want to take a picture that keeps everything from near to far in focus. You can do this by using a short lens (e.g. 28mm on a 35mm camera) and a small (f-11 or 16) opening. I don't want to get into spherical aberration. Trust me, smaller opening will give you more depth of field (and, you will need a slower shutter speed to let in enough light). Like this:
On the other hand, you may want to create an image with selective focus. That is, you want the main subject in focus and the things behind it (or in front...but I digress) blurred. To this end, you can get closer to the subject (the closer you focus the less depth of field you get), stand back and use a long lens and/or use a big lens opening (e.g. f-4, f-5.6). That will get you this:

Now you know everything. So, go take some pictures, and... Paddle safe...


DaveO said...

Boy, you get up earlier than I do! This is great stuff. As a guy who insists on a manual transmission, I appreciate the understanding and use of the manual camera settings. Too many things are 'automatic' and nothing more than a compromise. Long live the Nikon FM!

Ron said...

Now we know everything??? When do you share the magic of knowing how to put what your feeling into the picture?

Silbs said...

I knew I forgot something. Maybe another blog soon.