Basic Principles of Photography

In later sections we will learn about the relationship between shutter speed and aperture when correctly exposing a film to light.

At this stage, just remember that ISO will affect the other variables in the same way as they affect each other.

Light striking film causes a reaction in light-sensitive layers. The extent of the reaction is dependant upon the amount of light hitting the film.

Too much light will over expose the film causing it to go fully black (in the extreme case).

An exact amount of light needs to strike the film to get the best result ... Correct Exposure.

The amount of light required is not the same for all films - see film speed above.

Construction

The light-sensitive part of film is a layer (or layers) containing millions of tiny light-sensitive particles... compounds which react when exposed to light. The smaller the particles, the less sensitive to light they are. Therefore fast film has larger particles than slower film.

In slower films, the light-sensitive particles are far too small to see. Therefore, slow film - those with lower ISO numbers - will produce better-quality images.

In very fast film, the light-sensitive particles are actually big enough to see as a granular effect in images printed from these films.

So, the trade-off with fast film is grain size. But this can be used to advantage for artistic effect.

Black and White film:

As shown in the diagram, black and white film is constructed like a sandwich.

It is only about .3mm thick.

The top layer, or overcoating, protects against scratching.

The second layer is a light-sensitive emulsion containing millions of silver halides, constructed on a polyethylene base.

The anti-halation backing prevents light bouncing back through the film.

Film:	Film is the photographers canvas
Types of Film:
There are many types of film which can be used in a variety of applications (using the wrong film for a particular application is not a sin, it can be done for artistic effect) Negative [prints] Positive [slides or transparencies] Black and White Colour Infra Red Colour Balanced [daylight, tungsten] Variable speed Professional and a host of others not generally used for normal photography Digital - quickly replacing film and dealt with in a seperate chapter
Film Speed:
Film is rated at different speeds depending on its sensitivity to light. Each film is given a speed rating known as an ISO number (International Standards Organisation) for example; 100 ISO - probably the most commonly used film 400 ISO - popular fast film 1600 ISO - very fast film 100 ISO film needs twice as much light as 200 ISO film. Therefore 200 ISO film is said to be one stop faster than 100 ISO. 200 ISO film needs twice as much light as 400 ISO film. 3200 ISO film needs half as much light as 1600 ISO film. 3200 ISO is five stops faster than 100 ISO.
In later sections we will learn about the relationship between shutter speed and aperture when correctly exposing a film to light. At this stage, just remember that ISO will affect the other variables in the same way as they affect each other. How film works Light striking film causes a reaction in light-sensitive layers. The extent of the reaction is dependant upon the amount of light hitting the film. Too much light will over expose the film causing it to go fully black (in the extreme case). Too little light will under expose the film and leave little or no image. An exact amount of light needs to strike the film to get the best result ... Correct Exposure. The amount of light required is not the same for all films - see film speed above. Construction The light-sensitive part of film is a layer (or layers) containing millions of tiny light-sensitive particles... compounds which react when exposed to light. The smaller the particles, the less sensitive to light they are. Therefore fast film has larger particles than slower film. In slower films, the light-sensitive particles are far too small to see. Therefore, slow film - those with lower ISO numbers - will produce better-quality images. In very fast film, the light-sensitive particles are actually big enough to see as a granular effect in images printed from these films. So, the trade-off with fast film is grain size. But this can be used to advantage for artistic effect. Black and White film: As shown in the diagram, black and white film is constructed like a sandwich. It is only about .3mm thick. The top layer, or overcoating, protects against scratching. The second layer is a light-sensitive emulsion containing millions of silver halides, constructed on a polyethylene base. The anti-halation backing prevents light bouncing back through the film.
Colour film: Colour film has a similar sandwich construction but is more complex due to its sensitivity to the three primary colours, individually. Instead of one layer of light-sensitive particles, colour film has three light-sensitive layers. White light can be split into the three primary colours, red (magenta), blue (cyan) and yellow and it is these constituent colours which affect the three layers.	Cross section through colour film showing its various layers
Loading the film: Loading film is a simple process with most modern cameras. Place the film in the left side of the camera and pull out sufficient toungue of the film for the winding post to grasp, and close the cover. The film will be automatically advanced by the camera's film-advance motor either when the cover is closed or when the shutter release button is pressed for the first time. With an older camera, however, you must thread the toungue into a slot in the winding post. If this is not done properly the film will not advance. You can tell if the film is not advancing by watching the rewind handle. It should move at the same time as the film advance lever.
		Chapter 1 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Digital Cameras Assignment 1 Assignment 2

Film is the photographers canvas

Film Speed:

Loading the film: