35mm film cameras use a length of film enclosed in single-spool, light-tight, metal cassette to produce 36 x 24mm negatives, which is known by the terms “135”, or “35mm” film.
The idiom 135 was introduced by Kodak in about 1934, film and is little more than a numeric name to distinguish it from other film formats, e.g. 110, 120, 126, 127, 820, etc.
The alternative name of 35mm is descriptive of the width of the film, although in reality, the film is a tiny bit narrower than 35mm: it’s actually about 1 3/8 inches wide, or 34.9mm, because at its inception, 135 film was made by cutting another standard size film strip – 2 ¾ inch – in half.
The are four broad types of film; colour, black and white, print and slide, although black and white slide film has become pretty rare.
Print film is also known as “Negative”, since it produces a total inversion of the image captured (i.e. negatives), where light areas appear dark, dark areas become light, and colours (where present) are also switched into their respective complementary colours. The negatives are used to make prints, where the original image’s colours and tones are restored.
“Reversal” film produces a positive image on a transparent base. The processed film contains an accurate reproduction of colour, and light and shade, and requires no further treatment. Reversal film produces “transparencies”, which are commonly mounted in a plastic or card frame, and called “slides”.
All films have a “speed rating”, which is a measure of the film’s sensitivity to light. Films with a lower speed are relatively insensitive to light, require greater exposure to it, and are called “slow” films. Higher speed films are relatively more sensitive to light, require shorter exposures, and are termed “fast” films. There are three measures of film speed you need to be familiar with.
The DIN system (Deutsches Institut für Normung) was published in 1934, and is a logarithmic scale, usually comprised one or two digit numbers.
The ASA system (American Standards Association) was adopted by Kodak between about 1943, and 1954, and is an arithmetic scale, usually comprised of one to four digit numbers.
The ASA scale is easier to work with because the relationship between film speeds is simpler to grasp. For example, a 200 ASA film was twice as fast as a 100 ASA film, and a 400 ASA film was twice as fast as a 200 ASA film. In other words, using 400 ASA film in preference to 200 ASA allows the camera to utilize an aperture setting one f-stop smaller, or a shutter speed one-step higher. By contrast, when using the DIN scale it wasn’t as easy to fathom – on the hoof – that a 24 DIN film was twice as fast as a 21 DIN film, and a 27 DIN film was twice as fast as a 24 DIN film (you had to learn the speed increments).
In 1974, a new ISO (International Organization for Standardization) scale was adopted by the photographic industry, and this effectively combined the old ASA and DIN scales into one. In other words, 100 ASA or 21 DIN became 100/21 ISO, and 200 ASA or 24 DIN became 200/24 ISO. Cameras made before the mid 1980s may have ASA or DIN scales, or both. In reality most manufacturers stuck to the ASA/DIN system long after the 1974 changes.
There is one further film speed scale you will need to know about if you use a former Soviet Union made camera that pre-dates 1987: the GOST scale (but I’m not going to go into details here). GOST to ISO conversion tables are available on the Internet.
The relevance of film speed, of itself, it that is extends the capabilities of a camera to suit differing light conditions. For example, if you plan to shoot in a low light situation, or need to freeze motion, then a faster film is a good choice; but there is another aspect of film that needs to be taken into consideration, and that’s its “grain” or “granularity”.
Film is made from tiny fragments of silver, which under magnification look like gains of sand. They give film photographs their texture, which can be fine or grainy (or somewhere in between). Larger silver grains give film greater sensitivity to light, so faster films tend to have a more grainy texture, while slower films have fine grains of silver, and capture sharper images with much finer levels of texture attributable to the film. Today’s digital age equivalents of grainy and fine grain descriptions would be “noise” and “high-definition” images.
For this reason, the choice of film speed is often a compromise between ease of shooting (i.e. the ability to use faster shutter speeds/smaller apertures), and the quality of the photograph sought. Fortunately, most film manufacturers (and good retailers) describe the grain qualities of their products, and this allows the photographer to choose the film that best suit their needs based on both speed and grain.
Today, the big four film manufactures that once fuelled the rising in popularity of amateur photography are still in the business of making films: Agfa, Fujica, Ilford, and Kodak (plus a few others whose names have less kudos). I cannot recommend any particular brand of film: they are all good, and some are better than others, but the choice ultimately depends on what you are going to shoot and how you want your film photographs to look.