Found This Great Post By “The Discerning Photographer”, below I have posted a chunk, please visit their site for the complete article :)
Aperture: How It Affects Your Photography & Why You Should Care
Aperture diaphragm, Canon 70-200 mm f2.8 lens. (Copyright 2010 / Andrew Boyd)
Aperture: Now there’s a real ‘Photography’ word! Do you understand what ‘aperture’ refers to and how it affects your photography? Here I’ll explain exactly what it is and why you should care.
Simply stated, “aperture” is the hole in your lens that allows light to pass through to your CCD (charge coupled device) during an actual digital camera exposure. The size of the hole has a big impact upon your photos.
So what does this mean for your shooting?
Let’s start with how aperture works in your lens/camera setup.
If you’ve ever taken a lens off of a DSLR, held it up to a light and looked through it, the ‘default’ position that the lens will be in is at the largest, maximum aperture(sometimes even larger than the maximum aperture). If you’re looking through a 200mm f4 lens, for instance, then the wide-open hole will correlate with the ‘f4’ position on the camera. This f4 position will let the most light in, and also be the position with the shallowest depth of field. This just means that except for your point of focus, most of the other elements within your composition will tend to be out of focus. (‘Bokeh’ photography is all about this type of shallow depth of field shooting.)
Higher f-stop numbers correspond to smaller aperture holes: f2.8 or f4 will be a relatively large aperture (hole), while f11 or f16 will be a much smaller hole.
With a modern DSLR, you can see this by stopping your lens down to f8 or f11, then peering through the front element and pushing in the depth-of-field preview button. You’ll see the wide-open aperture hole suddenly contract down to a much smaller octagonal shape.
Try different f-stop numbers and you’ll quickly get a sense of how this works.
How does this affect your images? As you stop the lens down, say to f8 or f11, the hole gets smaller, and more things in front and behind your point of focus will appear sharp in your photograph. So large apertures = shallow depth of field; small apertures equal larger depth of field in your photograph. This can be a good thing or a bad thing, depending upon the photo you’re trying to shoot. The trick is learning to be in control of this phenomenon.
To really start to see how this can work, I suggest you operate your camera in a fully manual mode. As you change the aperture, making it larger or smaller, you’ll need to make a corresponding change to the shutter speed you’re using, since these two adjustments are dynamic and always work together. For instance, if your exposure is 1/125 sec @ f 8 and you want a shallower depth of field, you’ll need to open up the aperture, say to f2.8 or f4. Since you’re now letting all of that extra light into the exposure, you’ll need to increase the shutter speed to compensate and keep the overall exposure correct. I’ll address the creative and critical importance of shutter speed in another post, but for now, just use your camera meter to make the correct adjustment when changing the aperture.
Image at left is shot at f2.8, the image at right at f14. (Copyright 2010 / Andrew Boyd)
For the complete article, please visit: The Discerning Photographer