ISO - Film Speed

Film Speed – ISO The ISO rating of a film is a measure of the film’s sensitivity to light. High ISO films are more sensitive to light and therefore suitable for low light situations or when a fast shutter speed is required. Typical ISO film ratings include: ISO 100, 200, 400, 800, 1600 and 3200. Films with a High ISO are called fast films. Films with low ISO are called Slow films. The ISO rating is equivalent to the ASA rating: e.g. ISO 100 = 100 ASA, ISO 400 = 400 ASA etc. (ASA is an older ‘American Standards Association’ system).

High ISO rated films tend to be more ‘grainy’ Print from 1000 ASA film Enlarged detail from the same photo – note the visible GRAIN

Detail of a portrait made using100 ASA Film Detail when Re-photographed using 400 ASA Film. Note the increased GRAIN. Grain is composed of individual silver halide crystals which are larger and more ‘lumpy’ in high ISO films.

Two pictures taken using a Digital Camera High ISO (1600) Low ISO (100) Both images look very similar … but can you see a difference?

High ISO film or Digital Camera setting has LESS CONTRAST High ISO (1600) Low ISO (100) High ISO film or Digital Camera setting has LESS CONTRAST In these two images the high ISO image just looks a little ‘flat’ – colours appear less vibrant and overall the image has less contrast.

A small detail has been enlarged for each image. ‘GRAIN’ High ISO (1600) Low ISO (100) A small detail has been enlarged for each image. The High ISO digital image looks more ‘grainy’ than the Low ISO image. (The lower contrast of the High ISO is also apparent.)

Choosing which ISO film or digital setting to use Because High ISO films are more sensitive to light, they are ideal when: There is not much light A fast shutter speed is required A small aperture and fast shutter speed are required When a grainy look is required (for aesthetic reasons) 5. When less contrast is required (for aesthetic reasons)

Test Your Knowledge Which film is more sensitive to light, ISO 100 or ISO 400 film? Which film is more likely to allow a fast shutter speed in low light? Which film would you use in very bright sunlight? Which film would you use when working in low light conditions? Give an ISO setting suitable for recording fine detail with little grain

Which film ISO or digital ISO setting might you use … (there are no ‘right’ or ‘wrong’ answers to the following questions, but you must be able to justify your answer – to say why you have chosen a particular ISO) 6. A head and shoulders large poster size colour portrait of a female actor to be used for publicity outside a theatre. 7. A black and white photograph of a pile of rubbish. 8. A photograph of sports such as football in low light. 9. A landscape photograph taken using a tripod.

Prep work Produce a research page explaining ISO. Include what ISO is, how it affects photos and include your own images experimenting with ISO. Remember to link them to portraiture.