..When selecting the film you want to shoot a subject or scene with it is important to understand the different outcomes each type of film will produce. Most beginning photographer either do not understand the importance of having the proper film and exposure. For practical reasons we will only discuss 35mm type films.

Most 35mm films come in 20, 24, or 36 exposures. Knowing how many film exposures are on the roll is important especially if you are developing your own film. This is because the reel that your film is wound on when being developed usually will only hold a maximum number of exposures per roll. Probably the most important reason to have a short roll when beginning photography is they are easier to handle when you are rolling them in the darkroom. The disadvantage, however, is when you are shooting more than your roll can hold, you are often left loosing time reloading your camera and making your subject (if it is alive) impatient.

A film's speed is rated by a number called an ISO. ISO is an index for knowing your basic daylight exposure.

Basic Daylight Exposure Formula -

F-16 @ 1 / ISO

For example. If we were shooting a subject under basic sunlight (basic meaning non-ambient light, no clouds, no shadows) and our film ISO was 400, we would set our camera for F-16 and our shutter speed would be closest number on your shutter speed dial to 400. That would be a basic daylight exposure and we would know the ISO because it is usually printed on the box somewhere or even sometimes on the film roll itself. All cameras made in the last 50 or so years should have an ASA/ISO indicator dial somewhere on the camera body. If it does'nt you may want to perform an experiment to try to get your camera's basic exposure setting.

You are probably wondering what a "fast" or a "slow" film is. It is really very basic. A "fast" film needs the shutter to be open for a shorter amount of time to get the same amount of light a "slow" film would need. The higher the number that the ISO is the faster your film is. You are now probably thinking, well why not use the fastest film there is! Wrong. The faster the film the grainer the negative. The silver halide chrystals (the light sensitive element) in fast film are larger than those in slow film. Very high speed films are only desirable in capturing fast moving subject or for use in dark scenes. Slow speed films provide high resolution, but require there to usually be greater amount of light available to make a proper exposure.

Film ratings are divided into several categories:

Slow Speed............(ISO 20 - 50)... .....
Medium Speedd.....(ISO 100 - 200)
Fast Speed..... .......(ISO 400 - 500)... .....
Super-fast Speed ...(ISO 100 - Above)

When you are beginning you may not completely understand the effects of different film speeds, therefore it is safe to make a general recomendation for using film. ISO 200 - 400 will allow you to work with a great variety of light effectively. Slower and faster speeds will ofter only be used in planned or rare occasions. This ISO range will allow you to compensate for loss or gain of lighting as long as your camera has adjustable shutter and aperture dials. An example of this will be provided in upcoming sections.

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