Saturday, March 13, 2010

ISO (Exposure part 3)

This is part five in an ongoing series of things I'm learning in my photo 1 photography class. You can find the first four posts here:

-Photo Basics - Basic Definitions
-Photo Basics - Camera Controls and White Balance
-Aperture and Depth of Field (Exposure part 1)
-Shutter Speeds and Capturing Motion (Exposure part 2)


This post started out as my exposure post, but I realized it would be easier to quickly explain what ISO is on its own before explaining how ISO, shutter speed, and aperture value all work together.

ISO has its origins in film photography, where the ISO setting measured the sensitivity of a particular roll of film to light. Basically, the ISO is the speed with which your film/sensor responds to light. That’s it. Why that film speed is important, is because it controls how sensitive your film/sensor is to the light which also affects your exposure.

The ISO scale in full stops is: 25, 50, 100, 200, 400, 800, 1600, 3200, and 6400.

With film, a lower ISO sensitivity rating (like 50 or 100) means that more light, or a longer exposure, will be needed in order have a properly exposed photograph. Because of this, the film is considered a slow film speed. Film with a higher ISO sensitivity rating (like 400 or 800) will require less light, or a shorter exposure, to take the same picture. Thus it’s called a fast film speed. Even though the ISO doesn't let in more light like the aperture or the shutter, it does make your camera more sensitive to light which has similar results. Just like with shutter speed and aperture settings, moving to the next higher ISO doubles the amount of sensitivity to the light. Moving one lower halves it.


So basically:

Faster film speeds (higher ISO rating) – need less light.
Slower film speeds (lower ISO rating) – need more light.

So ISO 100 would be good for a sunny day outside because there’s loads of light. But if you tried to take the same picture indoors, your pictures would come out way too dark. (You can compensate for this somewhat with shutter speed and aperture, but I’ll get into that more tomorrow.) An easy solution would be to just switch to a higher ISO. And unlike film cameras where the film would have to be changed out in order to accommodate the loss of light, with digital cameras your ISO setting is only a button away (read your manual if you’re not sure how).

Now there is one important drawback to using a higher ISO (or faster film speed). When using a high ISO your camera will produce something called “grain” or “noise” in your photos. (“Grain” is used when referring to film and “noise” is essentially the same thing but in digital photographs.)

Now some people hate noise. I’m not one of those people. I think a little noise is fine but I’m pretty low maintenance when it comes to photography. This is one of those things that depends completely on your personal preference and on your cameras capabilities. Some cameras are better at taking photographs at higher ISOs then others. There is a gulf of difference between a camera that has too much noise because it doesn’t have the technical ability and a picture that would do for anything smaller then a billboard.

Cell phone pictures are great examples of “bad” noise.

Here are two examples of different ISO settings and noise:


As you can see the picture of Holden indoors has some obvious noise in the picture where as the one taken outside is a lot more sharp (if you click on the picture this will be even more obvious). This doesn’t bother me, but like I said its personal preference. Don’t forget that image quality with differ camera to camera (from what I’ve heard Canon are pretty good at taking photos in low light). We all got to work with what we got and trying different ISO settings is a simple way to get a better understanding of your camera.

So that’s it for ISO. Hopefully this was pretty straight forward and tomorrow I hope to have my last exposure post finished.

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