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4a.) Set the digicam's effective ISO on the Pentax meter. You figured out the effective ISO
from tests in 1.) above, which may or may not be the ISO indicated on the digicam.
4b.) Set the indicated exposure from the digicam on the Pentax scale. Don't move the ISO
setting.
4c.) Reset the ISO on the Pentax meter to your film's ISO. Don't move the LV ring. Now
read the film exposure off the Pentax scale.
A3 What are Shutter Speed, Aperture and ISO?
Introduction
These issues are very simple, in fact, so simple that they confuse beginners who worry
about them. In the old days before 1980 you had to worry about them, but today almost all
cameras just set these themselves in Program mode so we rarely need to bother
ourselves.
Rarely does one need to change apertures and shutter speeds away from what the camera
chooses at the Program setting. If you do need to change these, most SLR cameras have
a knob that shifts among the various equivalent combinations of aperture and shutter
speed.
Explanations
Shutter Speed is how long the camera stays open to expose itself to the image. Most of
the time it's just a short fraction of a second. The dimmer the light the longer the camera
needs to collect it to make a good looking image. At night outdoors without a flash this can
stretch into seconds or minutes.
If you want to change how motion is rendered you can use different speeds. 1/30 of a
second looks about natural for running water. 1/500 of a second freezes everything. For
sports use the fastest speed you can for most things unless you want deliberate blur.
Several full seconds will make waves look like a big, foggy blur.
Aperture is how wide the lens' iris opens. The wider it opens the more light gets in. It's
exactly the same thing as the iris of your eye which opens as the light gets darker. The
wider it opens for the same subject the shorter the shutter speed will be to get the correct
exposure. This is because the camera chooses shutter speed based on how much light
gets into the camera. A brighter subject or wider aperture lets in more light.
Big apertures have smaller numbers, like f/4. Smaller apertures have bigger numbers like
f/16. These are fractions, so 1/16 is smaller than 1/4. Big apertures like f/4 will tend to have
just one thing in focus. A smaller aperture like f/16 will tend to have everything in focus.
How much is in focus is called depth of field.
ISO or ASA is how sensitive your film or digital camera is to light. This depends on the the
film, and can be changed with special development called pushing or pulling. Digital
cameras can be set to almost any ISO. ISO is the same thing as ASA. We used ASA up
© 2007 KenRockwell.com 88 converted by Sándor Nagy