This is page 2 of 2. "Digital Photography" begins here.
Film speed is like the water pressure in the hose.
Slow film speed (low pressure) requires more time and gives more detailed results. Fast film speed (high pressure) requires little time but offers less quality.
Slow film speed quality.
Fast film speed quality.
As you can see changing any of these three will affect the amount of light hitting the “Image Sensor” inside your camera. Each affects the other two. If the exposure is to remain correct when you change one variable; one or both of the others must be adjusted to balance out the equation.
Let's see an example.
Let’s say a picture needs a shutter speed of 1/1000th of a second and an aperture opening size of f8 at a film speed of 400 ISO.
Now let’s say I want the tree branch in the fore ground blurred so as not to detract from the stage coach. I will need a larger aperture. That means substantially more light entering my camera if I don’t change either the film speed or the shutter speed. That would mean over exposure of the shot.
But, if I use a slower film speed, more light is required meaning the shot will not be over exposed. This is one way to balance out the change in the aperture opening.
Likewise, with the larger aperture, if I don’t change the film speed but speed up the shutter instead, ultimately the same amount of light will pass as in the original settings and the picture will still be properly exposed.
There are three main variables in digital photography. These are the three variables I will be working with throughout the pages on my site that deal with camera settings in digital photography and how to get what you want from your pictures.
Everything else is as it correlates to these three variables.
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