View Full Version : Controlling lighting in a picture

05-01-2007, 12:32 PM
From what I understand, the ISO is the shutter speed, and it determines how much light gets in, so setting a higher amount lets more light in during a dark situation.

How does this differ from setting the exposure compensation? Doesn't this also affect the amount of light entering the lens? I am using a Canon SD800IS.

Sorry for my ignorance.


05-01-2007, 04:42 PM
ISO isn't your shutter speed, your shutter speed is your shutter speed. ISO is your film speed or its digital equivalent. I don't know a great deal about how it works but im sure someone else will. What I do know is that your shutter speed and aperature control how much light enters (and also a number of other things). The ISO from what I understand affects how quickly that light is transfered onto the medium i.e. your film, or your digital sensor. That is what I gather anyways, correct me someone if I am wrong.

05-01-2007, 07:04 PM
ISO is how light sensitive your film is. Digital cameras can adjust the light sensitivity of their sensors, and the ISO name and measurements were kept because they have become standard in the world of photographers. ISO, shutter spead, and aperture all determine how much light is recorded by the sensor or film. ISO is the sensitivity of the recording medium, shutter speed is how long the sutter remains open to allow light to hit that medium, and aperture is the size of the opening of the lens.

So, by setting your camera to a higher ISO, you are making your sensor more sensitive. This allows it to capture more light faster. That's why ISO is also called "film speed." The trade-off with film is higher ISO film produces grainier images. With digital, it adds noise to the image. Some cameras and camera brands are better at limiting or removing that digital noise, one reason I like Canon cameras.

05-01-2007, 10:47 PM
You can also think of it in non-photographic terms:

ISO = size of your swimming pool (bigger number is a smaller pool)
Aperture = diameter of you hose (bigger "f" number, smaller hose)
Shutter speed = time

With a small pool, you can use a small diameter hose, and fill it (the "exposure") in the same time, more or less, as a larger pool (lower ISO) with a larger hose (smaller "f" number).

05-05-2007, 01:01 PM
My fiance got a glassy eyed look when I tried to explain this to her. Check out this link, it's layed out pretty well.