ISO? What’s ISO?
ISO is shown in numbers, and is an indication of how sensetive the film or digital sensor is to light. If you’ve ever bought film, you’ve probably seen numbers like iso 100, 200, 400 and so on. The higher the ISO, the more sensetive to light the film or sensor is, and the more grain (film) or noise (digital) the image will have.
Because there is more light sensetivity at higher ISO values, one can use higher shutter speeds and/or smaller apertures to perhaps, freeze the subject in low light situations or gain greater depth of field. Take care with ISO though, the higher you go, the more noise you get. Software can help reduce or remove this noise, but this has it’s limits. You may also wish to use use high ISO to take advantage of the creative effect that noise can bring. Experiment with it.
The images above have had the ISO increased by 1 stop for each. Open them up and see how the noise affects the image. Take note of the darker portions which is where the noise will generally be more noticeable.
ISO 100 is generally accepted as the norm and will give the cleanest images. Some digital cameras now go down to ISO 50. Consumer digital cameras have a general range of ISO 100 to around ISO 3200. Sensor type and size also affects how noisy an image will be a comparitive ISO’s. for instance, a £100 point and shoot camera will most likely be very noisy at ISO 400, whereas the full frame sensor of something like a Canon 5D will produce very clean images at ISO 800 or more.
Most consumers will buy a camera to take snapshots, leaving it in full auto mode. in this mode, the camera will select the ISO that is appropiate (trying to keep as low as possible). Many digital cameras, including the lower end point and shoot types will allow at least some manual control, and thus will allow ISO adjustment.
When choosing which ISO to use, there are a few factors i think of to determine this, these include -
- How bright is the scene?
- Am i using flash?
- Do i want the ambient light to register?
- Am i after a clean image, or would i like to introduce noise/grain for artistic effect?
If there is lots of light, my subject is stationary or fairly slow moving, and i want little to no noise i’ll proably use ISO 100 – 400.
Some situations which may call for increased ISO include the following -
- Indoor events such as a concert or sports event
- Wedding ceremony where there may be a restriction on using flash (which has an added benefit of being able to freeze the subjects motion)
- Art galleries or exhibitions where flash use may be prohibited
Any scene where the mood of the situation is better captured without flash will usually also require pushing the ISO up.
ISO is as important a tool in photography as shutter speed and aperture. learn it, use it. Experiment and have fun with it. Go as low and as high as you can go, seeing how it affects your images. Remember, when adjusting ISO, you will need to adjust your shutter speed and/or aperture as well to maintain the exposure you’re after (remember, the correct exposure is not always the creatively correct exposure).