Lesson One - ISO

ISO started it's life almost a hundred years ago as ASA. Both acronyms stand for the same thing, the sensitivity of the film (and recently a sensor) to light. Up until the late 70's this was known as ASA. It was at this point the film industry was making huge gains in technology, Fuji was starting to be a force to dealt with, and Kodak started loosing it's control over the photographic world, that's when the standard went from an America standard to an International standard - hence the change in name.

During this time things started to change. The ratings remained consistent but what you expected out of the film changed. During the mid-part of the 20th century most photographers shot slides such as Ektachrome 25 or Kodachrome 64. These slide films gave sharp rich colors, basically no grain, and were loved by everyone. They were the industry standard, and what all films were compared to. There was a problem though. You had to be shooting in bright light to get a good image. When they worked they were fabulous, but you had better have enough light or a tripod handy because they were limited. Tri-x the black and white 400 film that was available was another industry standard and loved by many. It gave you the ability to shoot in low light situations that color film would never work in. It has become a classic and is stilled used by many purists and students today. And as someone who remembers using it and loving it, and it is what I compare my bw prints to today.

It was during this time in the late 70's and early 80's that film made huge progress. Color film went through several changes, some more successful than others, but always with the idea that all films should be rated and the ratings should be standard so anyone can pickup a film and know what type of lighting this film would work best in.

ASA or today's ISO is a sensitivity rating that represents the light requirements for shooting a photograph. Today's cameras often start at ISO 100 and go up from there. When using a film camera your ISO is determined by the film that you purchase. Using a digital camera gives you the unique opportunity to change the ISO to match your needs for that particular situation. Digital cameras allow us to do what would have been impossible just 20 years ago...choose our sensitivity to fit our needs.

As a basic idea of when to use a particular ISO I will try to narrow down the choices for you.Please remember that the higher the number the more sensitive the film/sensor is to light,and the higher the grain.

ISO Situation

100 Daylight - for lighting situations where light is plenty and subject are
fairly stationary, or with flash inside. Grain will be almost nonexistent if exposed correctly, and enlarged within normal limits.

200 Daylight for normal situations, 2x more sensative than 100, is the lowest
setting on many digital cameras, grain will be very low if exposed correctly
and enlarged within normal limits. Flash probably be necessary for indoor shots unless very well lit.

400 Daylight - 2x more sensitive than 200 allowing you to use a lower shutter speed and stop some action. Will extend the effectiveness of a flash by picking up light at a further distance than lower ISO films. Great for low light, sports,or action situations. Grain will start to be obvious if not exposed correctly.

800 Best used in low light situations. Grain be obvious if not exposed
correctly or enlarged beyond a certain point. Great for sports, low light,
and for night shots.

1600 The top ISO on most standard model digital cameras. Newer and higher priced equipment will have higher options. Used for extreme low light. Grain is to be expected in most situations.

While today's cameras will have ISO numbers between the ones I have listed, you can get an idea from this list which ISO will allow you to get the effect your desire. And how it relates to your lighting, your choice of settings (aperture, and shutter speed) your lens choice and your final image. ISO is where is all starts and is the foundation of your image. It can make or break an image and is as important as any piece of equipment you can purchase.


Remember...

Live, Laugh, Photograph!

Maryann