Despite the bad weather we've had the last few days, I managed to make it over to Park Avenue and teach -- and now the first "Seriously Fun Photography" for 2010 class is ... ahem ... behind me.
That's good, as I continue to use a dumb acronym to force students to remember the three elements we need to master to understand and control exposure.
A. S. S.
That's right: we need to work with three related elements: Aperture, Shutter Speed, and Sensitivity.
The f/stops to memorize are f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22. If you forget these, make two columns, and at the top of the left one write 1.4 and at the top of the right one write 2.0. Now double each number as you go down the column (rounding off when needed). Changing one stop lets in twice as much light (or half as much, depending on which direction you go. f/2 lets in a lot of light, f/22 lets in very little light. So if you took a picture using f/8 and it seemed a little too dark, you would switch to f/5.6. If you took a picture using f/8 and it seemed a little too bright, you'd switch to f/11.
The common shutter speeds are:
1/1000th of a second
-- As a rule of thumb, if you are moving and you're subject is moving, you'll want to be shooting at 1/1000th of a second to get a sharp picture.
-- If you are still but the subject is moving along, it would be good to be at 1/250th or faster.
-- If you and the subject are both relatively still, you can probably handhold the camera as slow as 1/60th, but slower than that and you'll get a soft picture because of camera shake caused by pressing the shutter.
-- At speeds that are slower, you'll need a tripod to steady the camera, and probably want to trigger it using the self-timer or a release.
-- Many decent cameras have higher shutter speeds, and these are very useful for action or sports.
Notice that the relationship of these shutter speed settings is also doubling (or halving) the amount of light that hits your sensor.
This is the ISO "speed" of a digital sensor or of film. ISO 100, 200, 400, 800, 1600 and 3200 are available on many cameras (but not all), and you should take some test shots with yours to find out if the higher ISO settings are usable or not. Figure out the fastest ISO speed you find produces acceptable shots on your camera -- you'll need to switch to it sooner or later. Notice that each ISO speed is twice as sensitive (or half as sensitive) as the next.
At this point, we experimented with finding a good exposure for the lighting in our classroom. It turned out to be: f/2.8 and 1/125th of a second at ISO 1600.
Then we decided to start applying our general knowledge about the relationship between apertures and depth of field. While we start to get the idea when we say "f/2 -- shallow depth of field and f/22 - deep depth of field" actually trying this out in with some real world shots is always a good experiment.
So we set up an experiment: we set our aperture at f/1.4 and and focused on the eyes of a person sitting close to us. Upon reviewing the photo, we found that the that the person sitting further behind was out of focus. So, to see how depth of field changes, we ran through the whole series of aperture settings available finding the person in the background more in focus as we changed our aperture -- f/2 to f/2.8 to f/4 to f/5.6 to f/8 to f/11 to f/16 to f/22.
Since we were in manual mode, we had to change the shutter speed to keep our exposure the same while we ran through these apertures.
But then we realized changing manual settings can be slow -- so we explored using "Shutter Priority" and "Aperture Priority" as a quicker way to choose the factor that is most important to us, and let the computer choose the other setting.
We learned that a faster way to try this experiment was to switch to Aperture Priority mode -- then, we would pick the aperture and the camera would select the shutter speed -- so when we changed aperture, the camera would change the shutter speed and we were able to keep the same exposure.
We finished our class with an experiment in learning to see the environment around us -- finding assigned alphabet letters in our seemingly boring classroom -- and then with a game of photographic "telephone" -- about learning to communicate complex ideas through visual images.
Our homework: shoot a manual exposure, getting the best exposure you can and then checking this by looking at the image's histogram.
Then: try a series of shutter speeds with a moving object -- such as a spinning umbrella, a bouncing basket ball, or a hula hoop.
Next week we'll begin to look at composition, framing, and related issues.
Above: an iPhone snapshot from Tuesday. In Manhattan, it's important to be able to coordinate animal prints in any weather.