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Understanding Camera ISO Settings
Mastering one of the basic digital camera settings
So you've mastered the digital camera settings of aperture and shutter speed, but what is camera ISO and how can it benefit your photography?
Well, just like aperture and shutter speed, ISO gives you greater freedom over the exposure of your shots in different lighting situations - with side effects.
Essentially, ISO determines the parameters within which the aperture (what is aperture?) and shutter speed (what is shutter speed?) can work. It is a measurement of the speed in which film (in film photography) or image sensors (in digital photography) react to light.
The higher the ISO number, the faster the film/sensor. A fast film with a high ISO rating will form a picture, upon exposure to light, more quickly than a slow one. So the exposure balance that you set using the aperture and shutter speed controls will be dependent on the ISO setting you have selected on your digital camera.
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What does ISO stand for?
It's natural to assume that camera ISO is an acronym for some technical characteristic of films and sensors. In fact, it simply stands for the body who devised the measurement: International Organization for Standardization.
Maybe you've heard the letters ASA in connection with photography and photography exposure. This stands for American Standards Association, who previously defined the measurements of film speed.
They merged with the DIN (German Institute for Standardization) to become the ISO - and that's what the letters refer to!
A very similar ISO speed measurement system is used for both film and digital cameras (understanding digital cameras). When set to the same ISO speed, a digital and film camera - with the same aperture and shutter speed settings selected - should produce just about the same result.
So, 'what does ISO stand for?' isn't really the big question...
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How do camera ISO settings help with photography exposure?
We cannot control the brightness of the light source for most shots. Sometimes things are too bright: When looking to capture motion on a long exposure to create blur, strong daylight makes slow shutter speeds impossible without a neutral density filter.
Sometimes things are too dark: We've all taken shots on the widest aperture (with a tiny depth of field) and on a really slow shutter speed (causing camera shake), in a desperate attempt to capture some great subject under fading light.
It's in the latter situations, low light digital photography, where camera ISO is one of the most invaluable digital camera settings.
Of course, should a tripod (using and choosing tripods for digital cameras) be suitable for the shot in question, it is always the best option. Shooting on a slow shutter speed with the camera held steady by a tripod is a great way to create the right exposure.
But what about when you need to freeze motion and the blur created by a slow shutter speed won't do? What about when you're out and about and can't pull a tripod from up your sleeve!?
These are the times to crank up the ISO. Digital SLR cameras have increasingly fast camera ISO speed options. In your camera menus set the ISO to 300, 400, 500 etc until it becomes possible to create a well exposed image with suitable aperture and shutter speed settings.
It's amazing the effect that can be had once you move towards 800, 1600 or even 3200 - taking pictures at night becomes a lot easier. But...
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Side effects of fast camera ISO settings
Crucially, the higher the ISO is set to, the lower the image quality will be. So that's the trade off - a quickly formed picture for grainy, noisy results.
At around 300 and 400 ISO, the resultant noise is really no big deal. But up at the likes of 1600 it's a very evident feature of the picture indeed. Still - much better than missing a photo opportunity altogether!
To ensure high quality pictures in the majority of situations, it is a good rule of thumb to leave your digital SLR camera set to the lowest ISO speed available (often 100).
It is normally possible to select perfectly good aperture and shutter speed amounts within the parameters this affords. So get into the habit of adjusting digital camera settings for ISO only when really necessary.
This could end up being quite frequently. Tripods often aren't appropriate for night digital photography. When photographing people, an event or performance, you need to freeze the action. I have found that if an image is well composed and timed, the grainy effects of a high camera ISO setting are easy to overlook.
Also, always be ready to change camera ISO settings when doing low light digital photography indoors. If you're unable to change the intensity of artificial lights, ISO is one of the most important digital camera settings.
In this and other kinds of situations, there is often a decision to be made between notching up the ISO to create a well exposed, grainy picture and using the flash to produce a good quality photograph with totally flat lighting.
For me, the former almost always wins. I would recommend getting a feel for the speed at which you feel the camera ISO settings on your camera produce intolerable amounts of noise, and make a characterless flash picture preferable. This is just a matter of personal taste.
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