endless automata

You’ll find that taking pictures is a mix of artistic and analytical discipline.  Composition requires an artistic eye.  However. when it comes to light, photographers tend to be very analytical.  They use various numbers to describe exactly how much light is getting to the film, as well as how sensitive the film (or sensor, in the case of a digital camera) is.  The number used to describe film sensitivity is generally referred to as the ISO number of the film.

ISO stands for International Standards Organization and isn’t really important except for the fact that they standardized the scale that describes the sensivity of film.  Basically, the less sensitive to light film is, the more light that needs to get to it for a good looking picture to be taken.  Sometimes this involves exposing the film for a longer period of time, so very sensitive film is often referred to as faster than less sensitive film.  Sometimes you’ll hear this referrred to as film speed.

Some common film speeds:

• ISO 100 - good for bright sunlight - the least sensitive to light.
• ISO 200 - good for outdoors and some daytime indoor photography - twice as sensitive as ISO 100.
• ISO 400 - good general purpose film - twice as sensitive as ISO 200.
• ISO 800 - good for fast action photography and low light situations - twice as sensitive as ISO 400.

You may be wondering why we even bother with different film speeds.  It turns out that low sensivity film (like ISO 100) is less grainy (or noisy).  ISO 100 generally will give you brighter colors and less noticable grain than ISO 200, and so on.  Sometimes, usually when shooting in black and white, grain can be desirable, but most of the time, we want to avoid it - the basic rule is to use the lowest speed film you can get away with depending on how much light there is.

What about digital cameras?  It turns out the sensors used in digital cameras are very much like film.  Most cameras allow you to set the ISO speed of the sensor.  Many cameras use an AUTO setting by default, which means that the camera tries to use the lowest ISO speed possible.  Digital cameras are great for experimenting with film/sensor speed.  If you have a moment, try and take the same photo using a different ISO speed each time and compare the results (you may need to put your camera in P mode).  You may notice the camera taking a longer or shorter time to take the picture.  This, of course, is because you are changing the sensor sensitivity, and therefore requiring less or more time for the sensor to recieve enough light.  One of the ways the camera controls this is with something called the shutter.  I’ll talk about this next post.