With most cameras, however, you can change the ISO number and you will have a menu
item for doing just that. On selecting this, you will be presented with a list of
numbers and an "auto" option. This is likely to be the default setting for your camera
and, if you are a beginner, this is probably the best place to leave it. Your camera
will automatically adjust its ISO depending on how much light there is.
You might wonder why anyone would ever want to use any other setting, but there are
very good reasons. Not least of which is that part of learning photography is learning
to be in control of the photographic process and setting the correct ISO number is
an important part of that.
First things first. The higher the number you set, then the more sensitive your camera
will be. The scale is linear. That means, if you double the number, then your camera
will be twice as sensitive to light. So in simple terms, setting the ISO number is
quite straightforward. If the conditions are bright, set a low number and when it
get's darker, or you go indoors, change to a higher number. This is what an auto
setting will do, but there are times when this simple solution is not the right one.
Using a high ISO number will not only make your camera more sensitive to light, it
will also make the images it produces more "noisy". Just what this noise looks like
and how much of it there is varies tremendously between cameras. Not only that, but
whether the noise is a bad thing or not is a matter of personal taste. Some people
feel that noise can actually enhance certain types of photograph. In the heyday of
film, some photographers would deliberately shoot on high ISO material for its "grainy"
appearance. Grain and noise whilst being created in entirely different ways are visually
It is also possible to remove noise from an image, either with a good photo editor
or a dedicated noise reduction program. However, good as these solutions are, if
the highest quality is what you are after, nothing beats using a low ISO number in
the first place.
The two most obvious occasions when you would want to use the lowest ISO number,
no matter how dark it is, are landscape and night photography. In practice this means
using a tripod. Instead of making your camera more sensitive to light, you expose
the image for longer, hence the need of a tripod. This, of course, will work with
any static subject and your pictures will be noise free. You could always add noise
to your pictures in editing, but this way, you have the choice.
Not only are there times when you would want to use a low number when it's dark,
there are also times when you might want to use a high ISO even if it's a bright
sunny day. One reason is that it will allow you to use a very fast shutter speed.
This is important when you zoom right in or use a long lens on your Dslr camera and
are holding the camera by hand.
Long lenses greatly magnify the effects of camera shake and the only cure is to use
a faster shutter speed. In terms of overall image quality, it is probably better
to sacrifice some, in the form of increased noise, for the benefit of having a rock
steady shot. Also, if you want to make sure that everything in your picture from
front to back is in focus, then you need to use a very small aperture. You may find
that increasing the ISO number is the only way to achieve this.
One last point. If you want to start experimenting with different ISO numbers, the
first thing you should do is take a few test shots at each of your available settings.
Take a good close look at the noise each generated by your camera at each different
ISO level and make your own decision about how bad, or good, it is to you. Once you
know that, you will be able to make an informed decision about the best setting to
use, rather than let your camera decide for you. Who's taking this picture anyway?