When I am teaching my photography class, one of the first things I like to start with is understanding what ISO is. ISO is the same as Film Speed, but alas film is not around the way it used to be. However, the principles that were used on film cameras are the same as what is used in digital cameras. The difference is that you can change the ISO in camera with digital, but with film you have to buy a specific type of film and the whole roll would be that particular film speed. When understanding ISO, the first thing you should know is what exactly it does.
Film speed (or ISO) is a number given to film that tells how sensitive it is to light. A low number (ex. 100 ISO) means that the film is not very sensitive to light. A high number (ex. 1600 ISO) means that it is very sensitive to light. This is the same for digital, but instead you have the ability to change ISO directly in camera without purchasing different types of film. You are telling your camera how sensitive you want it to be to light.
When purchasing film at a camera store I remember people always telling me, use 200 for outdoor, 800 for indoor, and 400 for either. This was decent advice but it is not always that simple. What if it is night time, but you are outdoors? What if you are indoors, but there is a lot of light coming in? This is where knowing the ins and outs of what your camera can do can help you make a good decision with what ISO to use. I will be going over other factors in the next few months to help you make that decision and to also go into more detail of what different ISO’s mean. For now, remember this: The higher ISO you have, the more sensitive to light it will be, and the lower ISO you have, the less sensitive to light it will be.
