An online book of Common Sense Photography, by Rhett Stuart

How the Shutter and Mirror Work


Get really familiar with that camera manual to increase your photography skills! Knowing how to operate the camera and what its capabilities are is essential for great photographs! If you can work a computer a little or drive a car you can learn to work a camera! Not knowing how to work your equipment can really handicap a photographer! Of course you can leave it on "fully automatic" and the camera will maybe take good pictures a lot of the time. For those of you wanting to know and do more, read on...

Standard shutter speeds either double or cut in half the amount of light the camera sensor receives. The camera has the shutter mechanism in it just in front of the sensor. Shutters are usually operated electronically.

Standard shutter speeds are measured in fractions of a second. Standard shutter speeds are 1/2", 1/4", 1/8", 1/15", 1/30", 1/60", 1/125", 1/250" 1/500", 1/1000", 1/2000", 1/4000", and 1/8000" of a second. So using 1/30" of a second would allow double the amount of light as 1/60" of a second since 1/30th of a second is a slower shutter speed.

The shutter speed you pick can have a dramatic effect on your photograph.

Using shutter speeds of 1/30" and 1/15" of a second while hand holding the camera is very difficult. For hand held shots, figure about 1/125" second to help eliminate camera shake. Most sources recommend a slower shutter speed such as 1/30 of a second as minimum. Try different shutter speeds as an experiment. I think you will find 1/125 shutter speed eliminates a lot of camera shake which is more noticeable as the picture is enlarged on the monitor. Using a tripod can greatly help image quality and sharpness. Sometimes we have to use a slower shutter speed to make it work, but it probably won’t turn out as sharp if the camera has to be hand held.

A general rule to remember is to choose a shutter speed that matches or is greater then the focal length of the lens to prevent camera shake from ruining the photograph (focal length is explained in the next section). For example, if you are using a 100mm lens, chose 1/100th of a second or faster. For a 200mm lens, choose 1/200th of second or faster. If you are using slower shutter speeds, especially 1/60th or slower, try bracing your elbows against your sides, or against a wall, on your knee, or a ledge. Also, breathe out as you press the shutter. Breathing out or exhaling temporarily steadies our hands.

Pressing the shutter button sometimes shakes the lens a little while it is on a tripod. To avoid this, use a remote camera release, or use the shutter timer of 2 or 10 seconds. Also, some cameras have an optional "mirror lockup" feature that locks the mirror up when the shutter is pressed the first time. The shutter is released when the shutter button is pressed the second time. The reason for the mirror lockup is to prevent slight vibrations to longer telephoto lenses when the exposure is taken. I set my camera for a 2 second delay with mirror lockup. I press the shutter button, the mirror swings up, and 2 seconds later the shutter is released.

Your posture while holding the camera is very important also. Use the same posture for shooting photographs as for shooting guns. Also, cup your left hand under the lens. For slower shutter speeds, lean against a wall or brace your arms against your sides, or rest your elbow on your knee.

Distance doesn't usually matter for freezing the action. These pictures were taken about 100 feet apart at 1/80th second shutter speed. The bat was swung at the same speed (I could tell by the position of the bat during my 6 frames per second sequence of photographs). The bat has the same amount of blur at the same shutter speed at 5 feet and 105 feet away. The bat can't be seen due to the blur in both pictures.

Image stabilizers, or small electronics with a gyro that is attached to one of the glass elements in the lens, moves the lens element around to compensate for camera shake and can make slow shutter speeds less blurry. Of course, if your subject is moving the picture will still be blurred.

Shutters are usually rated by their fastest speed, such as 1/8000 of a second, and their expected length of life, such as being able to take 150,000 pictures before it wears out.

The SLR camera mirror is in front of the shutter. It reflects the image up into the viewfinder for us to view. The mirror flips up out of the way when we press the button to take the picture. Then the aperture steps down, the shutter opens briefly, exposing the sensor. As soon as the shutter is done exposing the sensor, the aperture opens back up, and the mirror returns so we can see again through the viewfinder. SLR stands for Single Lens Reflex and means we can see the image using the viewfinder through the same lens the picture is taken from.

Camera mirrors are rated by how they are operated. Some mirrors moved mechanically, and some are electronic. Some mirrors have a motor to raise it out of the way, and a spring makes it go back down. Some mirrors have two motors, one to lift it and one to lower it. When the mirror has two motors it speeds up the mirror so the black out, or the time the image blacks out in the viewfinder, is a much shorter time. Having two motors also makes the mirror quieter.

All standard camera settings for shutters, apertures, and ISO sensor speeds either double the amount of light that comes in, or cuts the amount of light in half.