ISO

ISO or ASA or film speed.

All of these mean the same. Once again ISO is how sensitive the film/sensor is to light. The lower the ISO number, the less sensitive the film/sensor is to light. If you have a lot of light, like a sunny day, then you can use a low ISO. If you are inside, you will have to use a high ISO. Remember with film, a high ISO will produce grain. With digital a high ISO will produce noise. 400 ISO (which was once considered fast) is now kind of in the middle.

The average digital SLR camera has ISO 100 200 400 800 1600. Point and shoot digital cameras may go lower and top out at 400.

Sample scene: ISO 100 1/125 f8 or f8 1/125

ISO 200 1/125 f11 or f8 1/250

ISO 400 1/125 f16 or f8 1/500

ISO 800 1/125 f22 or f8 1/1000

Hopefully you can see that each of these units is a stop apart. Maybe that will make things a little clearer.

Some digital cameras have ISOs that go 100 125 160 200 250 320 400 etc. These are just like film ISOs, so you have more choices. These are a third of a stop apart. Your shutter speeds and apertures are the same way.

Let’s say you want to shoot inside. You have a digital SLR camera with the stock zoom lens. You set your ISO to 400, take a meter reading and come up with 1/30 at f4. You want to hand hold your camera, so this won’t work. You then change your ISO to 800, take a meter reading and you come up with 1/60 at f4, this won’t work either. You set your ISO to 1600, meter and you get 1/125 at f4. Now you can shoot. You’ll have a lot of noise, but you can shoot.

My rule is use the lowest ISO you can.