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Taking
Pictures: What Film Speed Do I Use?
Your choice of film speed can have both
practical and visual consequences for your picture-taking.
In order to know the right speed that you will need, you
need to know its definition as well as some reassurances.
A
film's speed is photo jargon for its sensitivity to light. This sensitivity is indicated by its ISO rating, which is
printed on the box and on the film cassette itself. The higher
the number, the more sensitive the film and the less light
the film must gather from the subject to create an acceptable
image of it. With color print film, these speeds are typically
ISO 100, ISO 200, ISO 400, and ISO 800, though oddball speeds
such as ISO 50, ISO 160, ISO 640, ISO 1000, ISO 1600, and
even ISO 3200 are also available.
Film speed numbers are surprisingly straightforward in their
meaning. ISO 200 film is twice as sensitive to light as ISO
100 film. ISO 400 film is twice as sensitive to light as
ISO 200 film. And ISO 800 film is twice as sensitive to light
as ISO 400 film. (ISO 800 film is therefore eight times as
sensitive to light as ISO 100 film.) And the higher the number,
the more easily you can get pictures without flash in a dim
light.
You
don't have to set the film's ISO speed on your point-and-shoot.
The camera does it for you, by reading a metallic bar code
on the film cassette. By using this DX code, the
camera can calculate how much light the film needs for a
correct exposure, again, to produce a negative or slide that
makes the subject neither too dark nor too light, and in
the case of color print film, to create a negative that would
make the best possible print. The camera gets the right amount
of light to the film by adjusting the size of the lens aperture
(the window in the lens) and the shutter speed (the length
of time that window is open).
For example, the camera usually sets a higher shutter speed
if you're using a higher-speed film because the film needs
less light for a correct exposure than a lower-speed film.
Most point-and-shoot cameras don't let you manually control
the lens aperture or shutter speed settings, of course. But
your choice of film speed is still very important in terms
of getting the best picture quality.
It
is best to use an ISO 400 film as your standard print
film. Use films of other speeds only for particular situations,
lighting conditions, and printing requirements. Well-intentioned
photo store clerks may try to dissuade you from using an
ISO 400 film, which along with an ISO 800 film is called
a fast film because of the speed with which it reacts to
light. They may tell you that you need a slower film such
as an ISO 200 or even an ISO 100 for best results. They may
argue such advantages as finer grain, better color, and greater
sharpness. However, this advice is largely outdated, lingering
from times when using fast films involved considerable compromise
in picture quality.
The reality is that you're unlikely to see much, if any,
difference in quality between a snapshot-sized print from
an ISO 400 film and the same from an ISO 100 or an ISO 200
film. ISO 400 color print films are just so wonderfully good
that using them involves little trade off. For specific technical
reasons, in fact, you usually get better results than with
slower film — greater overall sharpness, improved color,
and richer detail.
You
can even use the sensational new ISO 800 color print films
as your standard film; in fact, the preloaded film
in most one-time-use cameras is ISO 800 film. Even in bright
light, the camera's lens aperture and shutter speed range
are such that overexposure is unlikely to be a problem
and the film tolerates overexposure very well anyway. (Note
that the highest speed available in Advanced Photo System
color print film and chromogenic black-and-white film,
both APS and 35mm, is ISO 400.)
Switching to a fast film (perhaps to do some low-light shooting
without flash) may mean that you have to get that slower
film (ISO 100 or 200) out of your camera. Do not shoot off
the remainder of a roll on any old thing or subjects that
you would not ordinarily shoot, just to use it up. You have
to pay for the prints, and you do not pay for prints of negatives
that you don't shoot. Get over it and push the midroll rewind
button. #
# # # #
SolveYourProblem.com : 2007
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