The last of the exposure trinity. Today we’re talking about sensitivity (ISO). We will learn what sensitivity is, how it works, and how to use it. Please check out the posts about aperture and shutter speed to better understand how it all works together.
What is sensitivity (ISO)?
Sensitivity is also called film speed. It tells you how much light needs to hit the sensor for an image to be created. Sensitivity uses a special ISO standard, that works in the same way as aperture or shutter speed. Each stop halves (or doubles) the amount of light needed for the same exposure. Higher the ISO, higher the sensitivity, less light is needed.
This is the standard ISO scale. ISO 100 needs double the amount of light as ISO 200 for the same exposure, while ISO 800 requires half the amount of light of ISO 400.
How does sensitivity work?
Imagine having a radio. If you increase the volume, you can hear whispers and background sounds a lot better. But you’re speakers start producing unwanted noise and hums. The same applies to sensitivity. Your camera uses complicated logarithms to amplify the light reading so that you can achieve the optimal exposure even in low light. But it comes with a price. With higher ISO colors start to appear washed out, details are starting to disappear, etc. If you look at this photo, you can see the noise. Every camera has a different way of addressing this ISO noise, but newer cameras are better at it, as technology becomes better and better. While noise does not make or break a photo, having no noise is better than having some noise.
Every camera is different. Trial and error is the key to finding out how good your camera is at a certain ISO. Take a few photos with different settings and see which ISO speed is the optimal balance between noise and quality.
How and when to use sensitivity?
Apart from noise, higher ISO has no visible effect on the image. It is merly used to achieve the optimal exposure once aperture and shutter speed had been set. Some cameras have a setting that automatically sets your ISO. That’s a pretty nifty feature, as you only set the maximum ISO (the maximum amount of noise you want in your photo), and your camera will do the rest.
Using higher ISO also helps you if you’re shooting with flashes. High ISO means that you can use less power when shooting, thus making your flash recycle times faster and reducing your power consumption.
This concludes the basics of exposure. Next week, we’ll look into composition.