Using the Aperture and Shutter Speed to
Achieve Quality Film Exposure
Guide to Photography – Film Exposure
Exposure in film photography is defined as the quantity of light that is allowed through the camera lens and onto the photo film controlled by the intensity of light (through the aperture) and length of time (determined by the shutter speed). For correct exposure in a film camera, whether 35mm, medium format, or large format, it is essential that you correctly set both the shutter speed and aperture. Film speed will also play a role in determining the correct exposure.
Obtaining the Correct Film Exposure
The correct film exposure does not exist as different photographers will have a different idea of what is properly exposed and what is not. See the example below for three different exposures of the same site. 
Depending on whether you want to see all the detail or darken it for night will determine the right exposure for you. However, the way in which you get any exposure remains the same.
Light Metering
Most modern 35mm single-lens reflex (SLR) film cameras have through-the-lens (TTL) meters that intake the amount of light available to help you determine the best exposure. These types of light meters are called Reflective Meters as they measure the light bouncing off your subject and into the camera lens. For beginners using a camera without a light meter, it is highly suggested that you purchase a handheld meter to use. Handheld meters can be Reflective or take Incident Light Readings. Incident readings put the light meter directly in the light of the subject to capture one light source instead of an overall average.
While successful, light meters often are very flawed in areas of great contrast. Because contrasting images may contain white areas, mid-gray areas, and black areas, the light meter is forced to take an average reading of average gray. This is of prime importance, especially in beach or winter photography, as the bright areas will be measured as mid-gray. A system was developed to compensate for the mid-gray exposure by exposing for the darker shadow areas. See zone system for more information about this.
Film Exposure without Light Meters
Metering without a proper light meter can be troublesome for most beginner photographers. However, there is a rule known as Sunny 16 which will dramatically help with exposure. Of course, a full knowledge of the zone system will dramatically help improve the Sunny 16 method. Essentially, Sunny 16 states that on a bright, sunny day, you set the aperture of your film camera to f-stop 16 and the shutter speed to the ISO film speed in use. Read more about this in the Sunny 16 page.