photo 101 - iso

Darrin Hill

In our last episode, we left our hero.. and left..

There is something i've always called "the golden triangle..'

Think of shutter speeds, iso, and fstops as the three points of a triangle.. The rule is... if you change one of these, you have to compensate by changing one of the others... more later, but just remember that..

Iso used to be called asa... means american standards association.. and now it's the international standards orginization..

when you used to buy film, they came with different numbers attached to the package. Each number was mathematically half or twice as another speed. THe numbers would indicate the size of the silver halide chrystals that made up the structure of the image. When exposed to light they would chemically change. The lower the number, the finer the grain, the higher the number, the bigger the grain. 100 would be like powdered sugar, 200 regular sugar, 400 bb's for a bb gun, 800 marbles, 1600 small rocks, 3200 big rocks, 6400 boulders.. (oh.. wait... did we see the half and twice as much as the one next to it thing?)
THe finer the grain, the more light you need... 100 speed would be a great outdoor high noon photo op.. but 3200 would be highschool nighttime football... cause it needs less light to expose itself... but you need 5 units of light more to use 100 speed film in the situation...

ok.. new definition.. the difference between each number will now either be called a unit or a stop... more later..

so why do we care now that no one (other than me) likes film? Sensors act the same way.. the higher the number, the less light you need... but the grainer (now called noise) the photo will be...

If you are shooting small images for a website, who cares? the difference in noise or grain structure really isnt noticeable until an image gets to around 8x10 or bigger.. BUT this will all relate to something later.... so it's the first bit to know when we get to lighting things..


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