Photography is all about light. It has to follow three easy but critical rules when it comes to proper exposure. (1.) ASA (iso) or the film’s sensitivity to light (the higher the iso the more sensitive the film is to light), (2.) aperture refers to the lens ability to open or close its diaphragm to light ( it is also called the f stop, the lower the number the wider the diaphragm opening), and (3.) shutter speed or the time the shutter allows light in (the higher the shutter speed the shorter it opens up to light and vice versa), all need to work together to achieve a proper exposure.
How do you apply this to photography
Depending on the lighting situation on a given day, all three components of the triad are constantly changing to accommodate for the proper exposure. In film, shutter speed and aperture has to accommodate for the selected fixed iso film until you change your film speed on the next reload. In digital photography all three can be changed to achieve a proper exposure. Remember, ISO, or ASA is the film speed, while in digital it is a feature that can be changed at any time.
ASA
In film photography an iso or ASA can range from 50, 100, 200, which are also called the low speed, and ASA 400 to 3200 are called fast or high speed film.
ASA can produce what we call grain or noise. The higher the film speed the more prominent these grains show up in your photographs.
Aperture
An aperture is a mechanism inside a camera lens that allows light to gather to expose the film.Aperture settings go from wide, 1.4, 1.8, 2, 2.8, 4, to 5.6, 8, 11, 16, 22. The lower the number the wider the opening on the lens and the more blurry the subject’s background. The higher the aperture number the smaller the aperture blade closes and the more detail it captures from foreground to background.
Shutter speed
A camera shutter speed can range from B (bulb), 2, 1, ½, ¼, ⅛, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000 etc. It is a mechanism in a camera body or the lens that allows light to come in briefly to expose the film. The slower the shutter speed the more motion blur it captures. This can capture motion effects like photographs of waterfalls usually set at a very slow shutter speed like 3 or 4 of a second. Anything handheld at shutter speed below 1/60 of a second can make the image blurry so a tripod is necessary to keep a static subject sharp. On the other hand the faster the shutter speed the better it freezes a fast moving subject. This is preferred in shooting sports or children at play.
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