Friday, January 23, 2009

Nailing the Exposure (3 of 3)

Sorry it's been so long since I've last blogged. Winter break was a blur and I'm back on campus now.

Our last component of exposure is shutter speed, or the time it takes for the mirror to go up and down and the image to be captured.

This is the last variable that I change while shooting and is my most often changed variable. So to recap: I set my ISO depending on the environment - base ISO (typically 100 or 200) for outdoors in sun and 800-1600 for dimly lit, interiors. I then set my aperture for the depth of field that I want. f/1.4 - f/2.8 for shallow depth of field, and f/3.5 and up if I need more depth of field. Remembering that the lower the number, the more light that enters. Lastly I set my shutter speed.

Shutter speed, as mentioned before, determines how fast your shutter *clicks*. This determines how long light can enter the camera and how long the shutter is recording for. A slower shutter speed lets more light in and a faster shutter speed lets in less light. Therefore, typically you will need a slower shutter speed in darker settings and a faster one in bright settings.

Shutter speeds are typically stated as a fraction of a second. If your camera reads "8000", it means that your shutter speed is 1/8000th of a second. 40 => 1/40th of a second and so forth. If your camera reads 1", 2", 3", etc. it means 1 second, 2 seconds, 3 seconds, and so forth.

Fast shutter speeds have these perks:
Help eliminate lens blur due to camera shake
"Freeze" action

The general "rule of thumb" for shutter speed was that you want to have at least 1/focal length as your shutter speed in order to prevent camera shake.
e.g. A 50mm lens should be shot at a shutter speed of at least 1/50. 105mm lens at 1/100, etc.

So why use slower shutter speeds? It seems like they do nothing! Wrong! Here are a few perks:
Let more light in allowing you to get a better exposure
Allow you to purposely "blur" images via panning
With a combination of flash and rear curtain sync, a slow shutter can show motion while freezing motion
Make awesome light trails, light graffiti, and star trails!
The one caveat is that you most likely want to have a good tripod support system to shoot with slower shutter speeds in order to eliminate camera shake (blurry images!)

I'll end with a few sample images and explain how shutter speed was used to make the image.

A slow shutter speed (1/30) was used for this image along with a panning motion to have a sharp car with blurred background

A long shutter speed (30") was used for this image to capture streaks of cars as they passed by.

A long shutter (1/8) with rear curtain sync and flash used

A fast shutter (1/1000) used to freeze the action of the race

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