| Customers are confronted by a massive choice of film when they walk into a proper photographic retailer. |
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Closest are black and white films. Further along the shelf are 'amateur' colour films. Out of the way, in a fridge, are the 'professional' films that are more sensitive to temperature. The only way to make sure you get the right film for your purpose is to ask the guy behind the counter. |
| Stated on every film is its speed in ASA. The higher the ASA the more sensitive the film is to light or the quicker an image can be captured. There is a trade off between the speed of a film and the level of detail it can reproduce. Slow films (eg. 25 or 50 ASA) are capable of very fine detail. Fast films (eg. 1000 or 3200) while capable of recording images at high shutter speeds or in dark places look fuzzy or "grainy". ASA stands for American Standards Association, the group that set the numbers. |
| From left to right; 35mm Kodak Royal Gold 25 ASA, 120 Agfa Ultra 50 ASA and 5'x4' Fuji Velvia 50 ASA. Films a professional might use. The black plastic thing is a "dark slide" for holding 5'x4' sheet film in preparation for use in the camera. | 
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35mm is for the most common type of camera. 120 roll film is used in "medium format" cameras which give a negative 6cm wide (ie. the width of the roll). 5'x4' sheet film is used in "large format" cameras which give a negative five by four inches (ie. the same size as the sheet). |