Aperture - At home, in the park, in the mountains

I think one of the most common, effective and essential techniques I've wanted to know how to do in taking photos is the "blurry" background effect, which I feel adds a sense of depth and drama to even the most "undramatic" subject.

I have found there a combination of ways to achieve this effect. The simplest on my Canon 550D is to simply go into creative mode and slide the "background blurry or sharp" dial down to blurry. This however is cheating, so I wanted to learn what was happening behind the cloak of creative mode.

Enter the world of "Aperture". So what is Aperture? http://www.photoxels.com/tutorial_aperture.html

In a nutshell, Aperture is how wide the lens of the camera is open, and accordingly, how much light get in. Aperture is measured using a f number - which operates in the opposite manner than would be expected:

• SMALL aperture number = larger lens opening = Lots of light
• LARGE aperture number = smaller lens opening = Minimal light

So what does this have to do with blurring backgrounds? From what I've learnt it's all about Depth of Field: http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

As it turns out:

• A small aperture number = larger lens opening = lots of light = shallow depth of field = blurry background
• A larger aperture number = smaller lens opening = less light = larger depth of field = sharp background

The way I try to think of it is as if my eyes were the camera lens. This is helped particularly by the fact that I wear glasses (I am short sighted). The principles are probably completely incorrect and the parallels between my vision and a camera are probably wrong, but it makes it easy to remember!

• If I take off my glasses and look around things close to me are in focus but things in the background are fuzzy. This is like having a small aperture number, as my eyes are wide open and lots of light is getting in.
• If I see something in the distance and wish to make it clearer, I squint, reducing the amount of light getting in, increasing my aperture number, making the entire image sharper. 

Other than the aperture value, the focal length of the lens (and also the "close-ness" of the object to the camera) effects the Depth of Field but this is something I will worry about learning for another day! http://www.all-things-photography.com/depth-of-field.html

For the time being, I am happy putting my camera on the AV setting, setting the aperture as low as possible, bringing the subject of the photo close to the lens and snapping away. My playing thus far has made me want to get more lenses with lower aperture abilities, but for the time being I still have lots to learn! The results?