Tuesday, February 2, 2010

Camera Basics 101: Aperture Explained

Aperture is a fairly simple concept to understand, and once you know the basics of it, you are well on your way to capturing the images you want to create.  The aperture that you set determines how wide open your lens is and how much light can get in.  A smaller aperture therefore needs a longer exposure to capture light than a larger one.

The numbers are backwards from what you might think, much like golf.  If your number is smaller, your aperture is larger and more open, letting more light in at once.  If the number is higher, the more closed and smaller your aperture.  Inside your lens there is a series of blades that come closer together or spread out more depending on these numbers.


There are many reasons to change your aperture.  The main reason being depth of field (how much of the image is in focus).  It also changes how powerful your flash output is.  If you have an aperture of f/22, you will need a VERY powerful flash for it to even show in the image.  Say your aperture is f/1.8, the flash will show up as a very bright light source.

Aperture can also be used to create a starred out looking sun, use a more narrow aperture around f/16 to create this effect.  The amount of blades in your lens determines how many lines of light are coming out of the sun.

When you use a small depth of field, the image has LESS in focus, and with a large depth of field, the image has MORE in focus.  f/1.8 will have much less of the overall image in focus than f/22.  The part of the image that is in focus is determined by where you set your point of focus.

The general rule for depth of field, is that based on your focus point there will be twice as much depth in focus behind that point, than there will be in front of it.  Therefore, if you are shooting a moving subject that is coming towards you, you will have a better chance of perfect focus if you pre-set your focus a little farther in front of the subject.  Fast-moving subjects are very tough to capture sharply, so it's best to pre-set focus at a point they will pass through.

When you shoot with a large wide-open aperture, the light is literally flooding from every direction onto your camera's sensor.  This creates a very bright image allowing quick shutter speeds.  With quicker shutter speeds it is easier to stop action, which is why many sport's photography images have a smaller depth-of-field.  However, the smaller depth of field also makes it tough to capture a quick moving athlete in perfect focus, because it gives you less focus space to work with.

Wide-angle lenses will give you a better depth of field than a telephoto.  The wider the lens, the better the depth of field.  However, if the subject you are shooting is close to the camera, you will get much less depth than a farther subject.  When shooting macro lenses (lenses that can be used very close to the subject) you can even have such a narrow depth of field that only a few millimeters of the subject are in focus!
f/3.5 105mm macro
Experiment with your aperture settings and all of this information will sink in quickly.  Memory cards are erasable, so shoot like crazy and you will become a much better photographer!

That's the BUZZ today! Please check back soon for more!


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