Mouse Ear Falls, Great Smoky Mountains National Park, Tennessee (#AT0011)
Footnote 1, the Basics: Aperture and Shutter Speed
The two variables that control the amount of light that strikes your
film are (1) the size of the lens aperture opening and (2) the shutter speed.
The f-stop ring on your camera lens controls the size of the
aperture opening. F-stop values are
printed on this ring and are calibrated as f/2, f/2.8, f/4, f/5.6, f/8, f/11,
f/16 and f/22. Each of these
aperture settings, or f-stops, is one-half the size of the next one.
The higher you set the f-number, the smaller will be the size of the lens
aperture opening. Thus, f/2 is
“wide open,” while “stopping it down” to f/22 results in a tiny aperture
opening (which in turn would require a much slower shutter speed to allow the
same amount of light in to strike and expose the film).
When you choose a specific aperture setting, such as f/11, your
“through-the-lens” light meter will suggest an appropriate shutter speed,
such as 1/125th second on a sunny day.
An understanding of the combination of these two functions of f-stop and
shutter speed is critical for determining the right exposure under the existing
conditions of ambient or natural light.
Modern cameras have TTL metering systems that are very good.
Your camera may, in fact, allow a choice of systems – spot metering,
where the camera takes its reading off of a central “spot” in the
field of view, or matrix metering, where the reading is taken off of many
nonrandom points across the field of view. Simply shooting at what your TTL
metering system suggests will often produce good results.
As you become more experienced, however, you will become aware that there
are many times when, for various reasons, you will want to underexpose,
overexpose or bracket (shoot once at the suggested exposure and at one or two
stops above and below the suggested exposure).
This is not difficult to do. To
underexpose by one “quantum of light” simply increase your f-stop setting by
one (for example, turn the f-stop ring from f/11 to f/16) or, in the
alternative, stay with f/11, but increase the shutter speed (for example, from 1/125th
to 1/250th of a second).
The f/16 Rule: This rule is often mentioned in seminars and photographic technique books. If you are ever concerned that your TTL metering system is not properly working, it may be a handy thing to know. On a sunny day, set your aperture at f/16. The appropriate shutter speed will be the inverse of the closest value to your film ISO or ASA. For example, if you are shooting with Kodachrome 64, at f/16 your shutter speed should be 1/60th of a second.
(Use Back Button on Your Browser to Return to Free Sample or Click Here)