Friday, June 11, 2010

Photography Tips- what are shutter speeds?

Photography Tips: What are shutter speeds?

The Shutter and Light:

Photography is defined as writing with light. When photography was first invented, people recorded images onto a material that was coated with chemical emulsion which reacted to light. The most common emulsion today in film photography is Silver Halide. This silver halide reacts to light in such a way that bright objects are recorded dark, because the chemical turns dark when exposed to light. Bright objects reflect the most light, and end up dark in the negative image. The dark objects don’t reflect enough light to alter the chemical, and it appears white in the negative. This is the basis for how photography works.

So if Photography is about recording light, then light is the single most important factor in recording a good image. There are three factors that contribute to a good exposure, Shutter Speed, Aperture, and ISO. In addition to the exposure of the image, each of these functions also controls other details in image making, that I will go further into in a second. For now we will just discuss shutter speeds, but I have other articles which explain Aperture and ISO.

The shutter in a camera is the only thing in the camera that physically allows light to enter and be recorded on the film or digital sensor. The other two settings help decide how much light gets in. When you press the button to take a photograph, you are telling the camera to open its shutter and close it again. Shutter settings decide how long the shutter stays open before it closes again. This is known as shutter speed.

How do I control Shutter speed?

If you’re using a film camera there’s a dial that has numbers ranging probably from 1 to 1000, or maybe higher. It will double in increments such as 1, 2, 4, 8, 15, 30, 60, 125, 250, 500, 1000. If you’re using digital, there will most likely be an LCD screen that has these numbers in sequence when you rotate one of your dials. You will want to refer to your SLR camera manual to understand which dial controls shutter speed. These numbers are actually FRACTIONS, not whole measurements. This means 1 stands for 1 second. 2 is actually ½ second, 4 is ¼ seconds. That means the higher the number, the least amount of time the shutter is staying open. The faster a shutter moves (like 1/1000) the LEAST amount of light is allowed to reach the film/digital sensor. This comes into play when deciding what a good exposure would be. If you’re images are too dark, your shutter speed is most likely too FAST, and you will want to pick a small number (i.e. a longer period of time) to get the correct exposure. Likewise, if your picture is too bright, you are letting in too much light and you will want to make the shutter speed faster. There are also numbers representing whole seconds, 1, 2, 4, 8, 15, and 30. The difference between these numbers and the previous ones is they will always be accompanied by a “. So instead of just 2, it will look like 2”. So if you’re looking at 2, it’s really ½ second and if you’re looking at 2” it’s 2 seconds. This means the shutter will be open for a whole two seconds, and you will be able to count it between the initial click and the final click.

What else should I know about Shutter speeds?

Shutter speed does NOT only control exposure! It also controls camera blur. There are many different types of camera blur. For example there’s camera shake and there is motion blur. Camera shake is when your hand is unsteady and the image is blurred, whereas motion blur is from your subject being in motion. Shutter speed can eliminate BOTH types of blur if it’s fast enough. This is because the speed of the shutter doesn’t allow enough time for the image to be recorded in motion. If the shutter is open for 2 seconds, however, your hand would definitely shake in that two seconds, and it records the starting point and the finishing point of an image in an overlap. With motion blur, it’s the same. It records the starting point and all movements being made in that two seconds. Also keep in mind that a subject moving towards you creates less blur that a subject moving parallel to the camera. This allows for you to use slower shutter speeds while still stopping the motion. This is where shutter speeds get creative. If you want the cool motion blur effect, I recommend using a tripod and leaving the shutter open longer. If you want a crisp, clear image, you’ll want a faster shutter speed. A really fun technique for motion blur is panning. Panning is when you move the camera in the same direction as the subject when the subject is in motion. So imagine you are photographing your friend on a bicycle and he is riding from the right side of the frame to the left side. Instead of letting him ride across the frame of your viewfinder, follow him with your camera, like you would a video, to blur the background and focus your friend. So he will essentially look frozen in a moving world.

What does the term stop mean?

A stop is just a measurement of exposure control. You will hear this term again when we go over aperture. All the numbers I listed earlier represent one stop of change. Most digital cameras will actually allow you to change the shutter in increments of 1/3 stops. This means you can be even more precise in determining exposure and speed.

A beginner’s field guide to Shutter speeds:

Type of motion Speed Camera-to-Subject Distance
25 ft 50 ft 100ft
Very fast walker (5 mph) 1/125 1/60 1/30
Child running (10mph) 1/250 1/125 1/60
Good sprinter (20mph) 1/500 1/250 1/125
Speeding car (50mph) 1/1000 1/500 1/250

A really cool example of panning: