Exposure: ISO – What Is ISO in Photography?

Now let me talk about the ISO. You probably have seen these numbers: 100, 200, 400, 800, 1600, etc. in cameras. They measure how sensitive the image sensor in your camera can be. An image sensor is where the light is converted into an image. It is usually a small rectangle inside your digital camera. Your pictures exists thanks to this image sensor. The light that comes through the lenses is “printed”, “stamped”, “scanned”, or whatever you want to call it, into this small sensor and sends it into a form of an image to your memory card. Image sensors are essential. One of the things that makes a good or bad camera is the quality of the image sensor. When choosing a camera we definitely want a good image sensor.

Image sensors’ sensitivity to light can be controlled. Each camera’s image sensor has a range of light sensitivity going from low to high. This is the ISO. When you set you ISO to a bigger number, the sensor becomes very sensitive to light. This will let you take pictures in low light conditions such as in indoor parties or sports, theaters, concerts, churches, etc. There is a drawback on doing this. The higher the ISO the higher the noise effect. The noise effect is the appearance of grain as shown here in this picture. If you want to have crisp pictures you will need lower ISO. A 100 ISO option is the normal rule. Some image sensors produce less noise in your pictures at a high light sensitivity than others. But generally we still want to keep the ISO low unless we really need it for poor light conditions, for really fast movements, or for extreme zooms or telephoto shootings without a tripod.

When we increase the ISO, the image sensor becomes very sensible to light and, therefore, you need less light. The shutter speed then needs to be open for longer time too and/or the aperture needs to be smaller.

I suggest playing less with the ISO leaving it in the lowest possible number and focus on aperture and shutter speed more instead. I modify my ISO when I can’t have a bigger aperture and a fast enough shutter speed combination. Depending on your camera model and/or settings, aperture mode or shutter speed mode won’t alter the ISO. So if you take a picture on Aperture mode at an aperture of f22 (which is a small aperture), the shutter speed will be open for a longer time, but the ISO will remain at whatever number you decide.

Now you know the exposure triangle. Aperture, shutter speed, and the ISO are the three things that affect the exposure of your pictures. It is important that you become really familiar with each one of these so you can take photography above the average picture everyone takes.


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