Your exposure for negatives should be for the shadow area that you want to have detail on your print. So if you want the shadow to have more detail you use wider aperture (smaller f stop) and a slower shutter speed. And less detail use a smaller aperture (larger f stop) faster shutter speed.
Your processing for the negative should be for the highlights and it's overall contrast. The film's development time will determine how white or grey the lighter areas of your print will be. To state the obvious if you over develop or under develop your film the highlight areas will be impossible to print correctly.
So increasing or decreasing the negative's development time does not affect the shadow density as much as it affects the highlights. So what does this mean; it means that by varying the amount of time you develop your film, you can produce a usable negative regardless of how contrasty or flat the subject may be.
So the general rules are as follows:
- Your exposure should be based on the amount of detail you want to have in the shadows/dark areas of your finished print.
- If your scene is very flat you can simply increase the negative's development time to make the high lights more dense. Which in turn will make the highlights on the print being whiter/brighter and less muddy. Some time referred to as N+.
- If your scene is extremely contrasty, you can compensate for this by giving the film less development. Some time referred to as N-.
A quick summary of this is, a longer devlopment increases the contrast and a shorter development time decreases the contrast.
Above I refer to N+ and N- what are these and what is N? Well N standards for Normal Development. Well for every film, developer and photographer there is a certain amount of development time that will produce a negative equal to the contrast to that of the scene. This is referred to as Normal Development denoted by the letter N.