[by Gheorghe Chistol]
This webpage was written to help students enrolled in SP.747. In the film-developing lab, all people realized that many photos were over-exposed for some reason. Hopefully this will help you figure out what could go wrong. I assume you have read the Silly Camera Numbers page.
ISO is the film sensitivity. It's a number, more common ISOs are 100
and 400. The higher the ISO, the higher the film sensitivity and the
larger the film-grain size. If you plan to shoot indoors in low light
conditions, film ISOs of 400, 800, or even 1600 are preferred. If you
are shooting outside and you have lots of sunlight, try to use ISO 100
film, or even slower (you can find films with ISO 50 or 25). The good
thing about low-ISO film is that the film-grain is very fine and you
have a lot of detail. If you are a diverse shooter, taking photos in
various conditions, stick to ISO400 film, such as Ilford HP5+, TMAX400,
Ilford Delta 400 and others.
Every time you load film into your camera make sure you tell the
camera what ISO film you are using. New automatic cameras should be
able to read the barcode on the film canister and know the ISO. If you
are using an older one, find the dial or the wheel that sets the
ISO. Even if you are using a newer camera, double check to make sure
that you and the camera agree on the ISO value:)
PS: Note about digital SLRs - the cool thing about Digital SLRs is
that you can change the ISO settings anytime. If you shoot film you
are stuck with one ISO setting for 36 frames. With digital SLRs you can
crank up the ISO up to 1600 or 3200 if you are shooting at night (so
you get reasonable shutter speeds and minimal blur). You can also set
the ISO to 100 on your digital SLR if you are shooting in sunlight,
such that you minimize noise and get maximum detail in the photos.
You have to control the shutter speed and the Fstop (aperture) on your
camera in order to get the pictures that you want. In older cameras
you have to set the Aperture (f/2.8, f/5.6, etc) and then vary the
shutter speed until the proper exposure is reached. Your light meter
should tell you what the proper exposure is (you might have a needle
light meter, or a meter with a red dot and a green dot, or something
like that).
In newer cameras you can use semi-automatic modes such as Aperture
Priority (labeled "A" or "Av") or Shutter Priority (labeled "S" or
"Tv"). In Shutter Priority mode you set the shutter speed (say 1/60
sec) and the camera automatically adjusts the aperture on your lens to
get the proper exposure. In Aperture Priority you set the Aperture and
then the camera uses the built-in light meter to adjust the shutter
speed in order to get the proper film exposure.
I almost always use Aperture Priority mode, and I recommend it to
everyone. It's easy if you know what you want. Suppose you want to
take a nice portrait of a friend. You
want a nice blurry background, therefore you want a low Fstop number,
such as f/1.8, f/2.8, or whatever the lowest number on your lens
is. You focus on the person's eyes, frame the photo, make sure that
the shutter speed is reasonable and shoot.
We are coming back to the
question, what is a reasonable shutter speed? It's something faster
than 1/50th of a second for most lenses that you are going to use for
this class (remember the inverse rule). On the other hand, your camera
has some maximal shutter speed limit, for the older cameras it's
around 1/500-1/1000 sec, for the newer cameras it's around
1/4000sec. Suppose you have your aperture wide-open and you are
shooting ISO400 film outdoors. I am pretty sure your camera will say
that there is too much light and even at the maximal shutter speed the
photo will be over-exposed (different cameras tell you that in
different ways, they blink, give you an error message, flash a red dot
at you, etc.). In this case you would have to stop-down (i.e. decrease
the aperture, from f/2.8 to f/8 for example).
Now suppose you are shooting indoors and there is little light
available. Even though light from fluorescent lights looks bright to
you, it might not be enough for your lens/camera. Then you have to
open the aperture on your lens all the way and try to achieve that
1/50 sec or 1/60 sec necessary for a steady shot (or use a tripod).
If you are able to understand what the Fstops and Shutter Speeds do,
you should be able to squeeze the most out of your camera. Remember, a
$100, 10 year old SLR camera can give you awesome pictures, and so can
even older/cheaper cameras. Ultimately it's all about you (having a
nice, auto-focus camera with a fast, sharp lens might help a bit though).