Exposure 101
In Exposure 100, we
learned about Film Speed,
Shutter
Speed, and Aperture. If you have not
read Exposure 100, please do
so before proceeding.
Once you understand film speed, shutter
speed, and aperture, we’re ready to discuss how these items relate to exposure.
This article will discuss how I think about exposure. This article covers
photography without a flash and discusses the use of a light meter built
into the camera.
Simply put, film speed determines how
much light needs to reach the film to record an image while shutter
speed and aperture, along with the available light, determine how much
light actually reaches the film.
The first step is to select a film.
I have already discussed films in my Film
Speed and Recommended Film articles. But
to reiterate, I recommend using the slowest speed film you can get away
with. My general recommendation is something like ISO 50 or 100 for landscapes
and macro work and ISO 100 or 200 for travel, recreation and wildlife.
After film selection, you will then
need to balance shutter speed and aperture for the given lighting conditions
to achieve the required light exposure to the film. This is where the camera's
light meter comes in.
The first question to ask yourself
is whether controlling motion or controlling depth of field is most important
in the image you are trying to make.
If
you are most concerned about freezing motion or intentionally blurring
motion, you will want to first select a shutter speed that creates the
effect you want. Select faster shutter speeds to freeze motion and slower
shutter speeds to blur motion. The camera meter will then generally tell
you what aperture is required to expose the film for the given lighting
situation. It is possible that, for the given lighting situation and the
shutter speed you select, there may not be an aperture available that will
work (your meter will tell you this). In this situation, you will have
to either find a way to dim or brighten the light intensity on the subject
(which you may not be able to control), switch to a faster or slower film,
or you simply will be forced to make sacrifices in your shutter speed selection.
More on using your camera meter below.
If
you are most concerned about depth of field, you will want to first focus
the image and select an aperture that creates the depth of field effect
you want. Select smaller apertures (such as f16 or f22) to maximize depth
of field or larger apertures (such as f4 or f2.8) to minimize depth of
field. You can choose this aperture by utilizing the depth of field marks
available on some lenses, by viewing the depth of field through the viewfinder
with the depth of field preview function activated (for those who have
cameras with this ability), or by judgment based on experience and practice.
Once the aperture has been selected, the camera meter will then generally
tell you what shutter speed is required to expose the film for the given
lighting situation. It is possible in low or extreme lighting conditions
that no such shutter speed is available on your camera. In this case, you
will either have to find a way to adjust the lighting situation (which
you often cannot control), switch to a slower or faster film, or you will
simply have to make sacrifices in your aperture setting.
Your Camera's Meter
Your camera's meter reads the light level reflecting from whatever you point
it at and determines the exposure setting required to make that subject appear
middle in tone (or brightness) in the final image. As you will learn in Exposure
102, "middle tone" is a brightness midway between white and black. It's
kind of a middle gray or medium green or medium red. Freshly cut green
grass or a ripe tomato are examples of medium toned objects.
The meter takes into account the speed
of the film you have loaded. You will generally select one of three camera
metering modes when determining your exposure. "Shutter Priority" metering
allows you to select the shutter speed and lets the camera select the appropriate
aperture for you. "Aperture Priority" metering allows you to select the
aperture and lets the camera select the appropriate shutter speed for you.
"Manual" mode lets you select shutter speeds and apertures and the meter
tells you when you've got the "right" combination.
As you will learn in later articles,
the use of Program or Auto Exposure modes let the camera control exposure,
not you. When using these modes, you place complete trust in your camera's
computer to determine what you want. While this actually works in many
situations, it is time to take control and stop using the Program and Auto
Exposure metering modes.
This is just the bare basics of Exposure.
To learn more, please check out my Exposure
102, and Exposure 103 articles.
