"[...] the process, activity and art of creating still or moving pictures by recording radiation on a radiation-sensitive medium, such as a photographic film, or an electronic sensor."
So, what is this "radiation" mentioned here?
LIGHT.
That's why images captured by cameras are called "photographs", a word coined in 1839 by Sir John Herschel based on the Greek φῶς (photos) which means "light", and γραφή (graphé) which, in this case, means means "drawing".
Now, capturing a "correctly exposed" image is all about letting just the right amount of light to hit/reach the film (or sensor in digital cameras). And, there are three things that allow you to do that. They are the shutter speed, the aperture, and the ISO.
These three things always work together, in a sort of balancing act. Allow me try to illustrate to you what I mean.
Let's say a camera has already been set to take a correctly exposed picture of a scene. If you change the setting of one of those three things (the aperture, the shutter speed, or the ISO), you will need to also change the settings of either or both of the other two. Let me show that to you graphically...
The blue horizontal line in the image below represents our "correct exposure". I have lined up the aperture, shutter speed, and ISO on that line to represent that their combined settings produces a correctly exposed picture. This will serve as our "original" setting. (Note that this does not mean that they are set to the same values as they are measured in varying units).
If you reduce the aperture opening, you will either have to use a longer shutter speed or use a higher ISO to maintain the same exposure as the original setting (as shown below).
In some cases, like if you reduce the aperture opening even further, you MAY have to increase both the shutter speed and the ISO to achieve the same exposure as the original setting (as illustrated below).
So, like I said, it's a delicate balancing act.
Remember those three things--aperture, shutter speed, and ISO.
Of course, the camera can only do so much; the quality of a picture still depends on the skill of the photographer. Make sure to claim your copy of "Shoot Digital Pics Like the Pros," to get professional photography tips and tricks. It's a totally f-ree report.
You're probably wondering now, if your camera has already been set to take the correct exposure, WHY ON EARTH would you want to change the settings?!
Aah... I'll be talking about that in some future posts.
'Til then.
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