Friday, February 28, 2014

Shutter Aflutter: Photography Basics: Part 2

Photography Basics Part 2: Shutter Speed

See Part 1
Part 3

In this week's episode of "photography basics," we will be talking a little about what shutter speed is and how you can use it to improve your images.

So, what is shutter speed?
In last week's post, we talked about aperture, and how it helps determine how much light reaches your film. Well, the shutter is like a curtain that sits between the aperture and the film/chip. The speed at which the shutter is raised up and down determines the exposure time - how long light is allowed to hit the film.

So what does that mean?
A fast shutter speed means that the film is exposed to light for a shorter time, while a slow speed allows for a longer exposure - and thus more light. Of course, the aperture size also impacts how much light reaches the film.

Shutter speed is expressed as a fraction of time, say 1/250 seconds. Thus, a larger number indicates a faster speed, and also less available light for the exposure. A darker setting, for example indoors or in the evening, will generally require a slower shutter speed and a larger aperture to permit enough light to reach the film to make a decent exposure. Conversely, a bright setting, such as a beach at midday, will allow for a faster shutter speed and/or a smaller aperture.

These decisions are artistic as well as technical.

So does it matter to me if I need to use a slow shutter speed?
Well - yes. As mentioned above, a slow shutter speeds equals a longer exposure. Thus, any movement that occurs in the frame during the time of the exposure will be recorded.

Taken with a shutter speed of 1/60 at f/6.3, and a focal length of 100mm
You can see here that a slower shutter speed shows movement as blurring in the frame. You can use this to your artistic advantage to create interesting depictions of motion. However, it can also work against you. A shutter speed that is too slow allows for unwanted blur in the image, particularly if you are shooting with a long telephoto lens. This is called "motion blur." It occurs either because you moving the camera slightly as you shoot (get a tripod!) or because the animal/subject has moved suddenly in the frame.

A good rule of thumb to avoid motion blur is to shoot at a shutter speed of at least 1/focal length. So, for example, if I am shooting at 300mm, I don't want to be using a shutter speed of under 300 without a tripod to stabilize.

Here is an example of motion blur! It's not pretty - this photo is no good. Shot at a shutter of 1/40 at f/5 with a focal length of 200mm. The shutter is not fast enough to stop the motion of the bird.
So then what does a fast shutter mean?
A fast shutter speed means that the film is only exposed to light for a very brief period of time - thus, you need to be in a situation with a lot of available light.
A fast shutter speed is able to "freeze" motion, and can be good to capture detail in action shots and avoid motion blur, as discussed above.
Osprey at Bowman's Beach, Sanibel island. Shot at 1/1250s, f/5.6 with a focal length of 300mm
Here you can see the difference the fast shutter speed makes! The osprey is frozen in flight, with all of the detail preserved, and no blurring. It is artistic preference whether or not you choose to shoot motion like this or with a slow shutter.

Hummingbird Moth - 1/640s, f/5, focal length of 100mm
This is an example of an intermediate shutter speed. You can see that it is not fast enough to "freeze" the motion of the moth's wings, but it is able to stop motion of its body. Thus, you get detail preserved in the body of the insect and a soft blurring of the wings, representing flight.

I personally prefer the look of images taken with fast shutter speeds, so I usually set my camera to the largest (widest) aperture available to allow for the most light and the fastest shutter. Of course, sometimes I make adjustments to the aperture to create different depths of field - it all depends on the look I am trying to achieve. 

I hope that this article was helpful and allowed you to understand a little bit more about those funny numbers on your camera! If you're interested, here is Part 3 of the series.

Which look do you prefer - fast or slow shutter?

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