Overexposure/Underexposure

[Sydney]

What are the results of overexposure and underexposure? Is the result of
underexposure an overly dark picture?
BTW, since many of my pictures end up ruined, I'm thinking of buying a light
meter. What exactly does a light meter indicate? Does it indicate the
exposure time and setting that you should use? What's a good one that is also
cheap?

[Don]

Draw a flattened letter "S" on a sheet of paper. The central
portion of the "S" should be straight. It should slope from upper
right to lower left at about a 45 degree angle.
This is the exposure curve for your film. The top of the curve, where
the "S" flattens out to the right is the over exposed area. The
bottom of the curve where the "S" flattens to the left is the shadow
or darker area. The linear portion that is straight is the normal
range of exposure.

Now you can see that if you expose to push your image up the scale,
(over expsoure) the highlights will reach a point where they can no
longer record information, because they have flattened out and are
totally white. The film's or CCD's range of exposure has been
exceeded.

Conversely, if you push your image to the lower end of the curve,
(under exposure), you will reach a point where the invormation on the
film or CCD is solid black and again, no information is available.

Under exposure (about a third of a stop) will improve color
saturation. In some cases you can set your expossure system to provide
this automatically by setting your EV control to -.3. This is
particularly good for flat lighted scenes (dull days and cloudy
overcast skies).

If you are looking for a "High Key" effect (very flat lighting on a
white background -studio work) you may want to slightly over expose to
get that effect. However, watch out for your main subject, you don't
want that to go too light.

Every scene doesn't call for under exposure. If the scene is very
contrasty (bright highlights and deep shadows) placing the image on
the straight portion of the curve so that you can be sure that you
have detail in both the shadows and the highlights, is the right
approach.

Back in black and white days we use to say expose for the shadows and
develop for the highlights. That is, be sure you record shadow detail
and then when you develop the film be sure you don't block your
highlights with exceesive development. This is for negative images of
course.

Hope this helps.

[alistair]

Sydney
If lots of your pictures are currently lost through poor exposure then buying a lightmeter will probably be of no help.
How do you currently calculate exposure ?
Do you let the camera do it for you or do you guess ?
If you are guessing then why ?
If you let the camera do it then you already have a lightmeter and maybe need to learn a bit more about how to make the most use it rather than buying a separate lightmeter which you won't be able to make full use of yet.
Nice explanation of Characteristic Curves from Don but I suspect that isn't what you are after.
If you tell us a bit more maybe we could offer more specific help.
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alistair
http://www.silverlight.co.uk

[Georgews]

If your camera does not have a built-in meter you should get one, but most cameras now have them. If you can adjust your shutter speed and aperture and you do not have a meter you could try the old f16 trick. On a bright day set the shutter speed to the ISO rating of your film and the aperture to f16. As the day gets duller open up the aperture - overcast but bright maybe use f11, dull use f8 and so on. This should put you in the ball park for an acceptable exposure.
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George