When photographers discuss exposure, they mean the amount of light entering the lens and penetrating the film or CCD sensor. Exposure is the meat and potatoes of photography. Without light, there would be no image.
Modern day digital cameras by default come with a series of settings that automatically adjust the exposure without any worry from the photographer.
So why bother manually adjusting your exposure when the camera does such a wonderful job?
There are many reasons.
Probably one of the biggest arguments is the fact that the camera will readjust the settings anew every time you push the shutter button. Which means the slightest change could completely throw off the exposure settings from the previous picture.
For example, if you took a picture of a person wearing a red shirt. The camera would adjust the camera to properly expose the persons skin tone, the red shirt, and the background. Now, if you wanted take a second picture with the person in red standing beside a new person wearing a dark brown shirt this could completely throw off the pictures exposure. The camera will now try exposing the dark brown shirt as much as possible. This will in effect cause the skin tone to be more washed out and brighter then the previous picture. As your scene changes, so will the cameras exposure settings. Taking a series of pictures in one place could result in a variety of exposed pictures.
One benefit of having control over your exposure is experimenting; allowing as much or as little light as you want. Being creative with your exposure can result in some pretty amazing shots:
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| Over Exposed | Under Exposed |
So, now that
you are prepared to use the manual settings, how
does it work?
Every camera has a shutter
diaphragm. It's essentially a circular doorway to the film or
sensor. Imagine a futuristic spaceship door from Star Wars or Star
Trek and you wont be too far off. As you press your shutter release
button (the button that takes the picture) the diaphragm opens and
closes allowing light to pass through into the camera. There are
two functions that control the diaphragm, the aperture and the
shutter speed.
When looking at your cameras display, you will notice a f-number. It will look something like F5.6. This is your f-stop or fraction number. The f-stop controls the aperture size, or how much the diaphragm opens. The theory behind how f-stops work can be quite complicated. So for now, let's just stick to a simple formula:
The f-stop number controls how wide the shutter diaphragm opens. The lower the number is on your display, for example F2.6, the wider the diaphragm will open and the more light will will expose your picture. The larger the number, for example F8.0, the smaller the opening and the less light will be let in.
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| F8.0 (Less Light) | F2.6 (More Light) |
Your lens greatly effects how wide your aperture can go. Most stock lenses will have an f-stop range of F3.5 to F16. If you own a SLR camera and decide to purchase a new lens, you can get lenses that allow your aperture to go as wide as F1.4.
Aperture also plays a role in controlling the depth of field. The larger the aperture is (F2.0) the shallower the depth of field is. Thus the more blurry the background would be.
| Image | Image |
| F1.8 (Shallow Depth of Field) | F8.0 (Wide Depth of Field) |
Now that you know the aperture controls how wide the diaphragm opens - now we can move on to the shutter speed and that it controls how fast the diaphragm opens and closes. When snapping a picture, the button you press to take it is called the shutter release. It tells the shutter diaphragm to open and close and how fast. You will hear two click sounds. That is in fact, the sound of the diaphragm doing its thing.
Along side the f-stop number, you'll notice another number which looks like 1/100 or 1/60. This is your Shutter Speed. The number is how fast the diaphragm will open. For example: 1/100 means 1/100th of a second. Normally that would be considered pretty darn fast. When it comes to photography, 1/100 can be considered slow. You can increase your shutter speed up to 1/1000 which equals 1/1000th of a second. Super fast.
Like opening and closing the
size of the aperture, how fast the shutter opens for also effects
the exposure. The faster it opens the less light gets in. You have
to balance between your shutter speed and your aperture to control
your image.
So what are
the advantages of the shutter?
Have you ever
taken a photo in a darker situation and it turns out blurry because
you're hands shake a little. This happens because you move a little
while the shutter is open at a slower speed. Yo only notice this
when the shutter goes below 1/40sec. The shutter opens for a lot
longer than it would at 1/1000sec. So it picks up more
information.
Using a tripod in conjunction with longer shutter speeds can produce some pretty cool effects (see River image above). It also removes the chance of "shaky" pictures.
So how do I use Aperture and Shutter Speed together?
Depending on what you want to accomplish with your photograph you would use one and readjust the other. For example: If you wanted to take a picture that had a shallow depth of field and a lot was out of focus, you would set your aperture as low as you possibly can get it (F1.8). Because now your aperture is wide open a lot of light will be exposing your picture. You can adjust your shutter speed to a higher speed in order to let less light in.
On the flip side, if you
trying to shoot a picture with a lot of motion blur you will need
to set your shutter speed to a low speed (1/20sec). This will also
let a lot of light in. In order to balance the exposure you will
have to close your aperture.
One of the most commonly used techniques by photographers is bracketing. It is more of a safety blanket, rather than a technique. When taking a picture, you take a series of three photos. The first should be at the exposure you feel is correct. The second should be one f-stop under exposure, and the third should be one f-stop over exposure. This is best done when you have the chance. Run and gun photography doesn't often allow for this.
For example:
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| One f-stop over (F2.4) | Correct Exposure (F3.4) | One f-stop under (F5.6) |
When downloading your photos to your computer you will have a choice of three exposures. You may catch a photo that looks better slightly over exposed or under exposed. This technique is best used when you want to capture a very important picture.
If you don't
want to effect your depth of field, try bracketing with your
Shutter Speed.
Although you can't see how the settings will effect your photo until you've taken the picture. Over time you'll be able to assess the situation more easily and more often than not you will correctly expose your picture on the first or second try. Or at least be pretty close.
Don't get frustrated if you
don't get it right away. Most photographers use a light meter or
take multiple pictures over a variety of exposures. It will come
with time, practice and after taking a LOT of photos.
Homework: 'Expose yourself'
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