‘ISO’ – Part 2 of a series on “Going Manual” with your camera…
To leave ‘auto’ behind and control your camera you work with manual settings. Previously, I mentioned ‘exposure’ is the total light that the camera records on the image sensor during a shot. The three settings in the manual control of exposure are…
- ISO – the light-sensitivity of the camera sensor;
- Aperture – the amount of light coming through the lens;
- Shutter speed – how long the sensor is exposed to the light.
The camera image sensor records the light to make a picture. It has its limits. If foolish enough to look directly at the sun you’d see only a bright, featureless disc (shortly before going blind!). Like us, the image sensor cannot record great brightness. The detail ‘blows out’. Very bright spots become a pure white. No detail shows. Very dark areas are the same. Our eyes cannot see into the gloom, sensors cannot either. Detail is lost in deep darkness too.
Our eyes see about twice the range of light a camera records in one shot. Our eyes are fixed in that one, but wide, range. We cannot see brighter or darker than our eyes were meant to see.
Cameras, on the other hand, can see into higher and lower ranges of light, but not both at once. By changing the sensitivity of the image sensor they can get into the upper or lower end of the range. This is useful because in bright light you can record a picture without losing detail. To do this you make the image sensor less sensitive. In darker places you can increase the sensitivity of the image sensor. This will allow the camera to ‘see in the dark’. What a camera cannot do is see very dark and very light at the same time. Change the sensitivity and you must shoot a new image.
The ‘ISO’ control changes the sensitivity of the image sensor. On digital SLRs the setting ranges from around ISO 100 to many thousands (depending on the model). In bright conditions we use the low numbers (ISO 100). However, in darker situations we push up the ISO setting. Here are some typical settings as guidance to use with hand-held shots…
- ISO 100 – bright sunny outdoors; under studio lights;
- ISO 200 – cloudy bright day, not in direct sunlight;
- ISO 400 – cloudy grey day – no direct sunlight;
- ISO 500 – stormy day; deeply shady place outside; indirectly lit room;
- ISO 800 – a darker room/church; a stormy day in trees; after dusk;
- ISO 1000 – a very gloomy location!
In some situations you might not want to use flash or might not be allowed to use it. Public places often don’t allow flash. Raising the ISO means you can still take the picture in darker situations. See “Shooting in Low Light Without a Flash”.
Setting high ISO is not without problems. High ISO creates ‘noise’. The result is a grainy texture on the picture. The slightly speckled result affects the picture, lowering the quality (See the “Red Pepper” enlarged ). Some people consider this loss of quality a type of texture. On film the ‘grain’ was sometimes considered to impart a charming character, but it’s better to avoid noise. The nearer you set ISO to 100 the lower the noise. However, modern cameras are pretty good at preventing noise.
So, there you have it. ISO controls the image sensor sensitivity to light…
–> High ISO – you can see in darker scenes, but noise levels go up.
–> Low ISO – you can work in brighter scenes – low or negligible noise.