Shutter Speed / Aperture Relationship

[savona]

In order to get the desired exposure in a photograph you have to use a combination of shutter speed and aperture. Many combinations will achieve the same exposure, but understanding how these two setting effect each other will help you to make more professional images.

First we will start with shutter speeds since they are a lot easier to explain and understand. First the shutter is basically a curtain that covers the film leaving it in the dark (or sensor in you digital camera). When you snap your picture the shutter will open and allow the light to hit the film/sensor.

Now shutter speeds are measured in seconds and fractions of a second. The longer the shutter stays open, the more light enters the camera. Simple right?

Shutter speeds use a sequence of stops which either halve or double the amount of light reaching the film/sensor. Here is a scale of shutter speeds from an average camera. Some cameras may have a faster shutter speeds (higher than 1/1000 sec) or even slower shutter speeds (some low as 30 seconds). But in any case you will ALWAYS be halving and doubling the amount of light reaching the camera by halving and doubling the time the shutter stays open.

8 sec - 4 sec - 2 sec - 1 sec - 1/2 sec - 1/4 - 1/8 - 1/15 - 1/30 - 1/60 - 1/125 - 1/250 - 1/500 - 1/1000

You can see above that 2 seconds is twice as much as 1 sec (doubling) and is also half as much as 4 second.

Ok, thats fairly simple right? Now let us move on to aperture or f-stops.

Aperture is the opening in a camera lens through which light passes to expose the film. A wider opening will allow more light onto the film/sensor a narrow opening will allow less light into the camera.

Aperture works similar to shutter speed as they both halve and double the amount of light reaching the camera. At a quick glance you may be confused by the numbers for the f-stop settings. This is normal, once you understand how the numbers come to be, you will see the light (no pun intended).

The f-stop numbers represent the ratio between focal length and diameter of any given lens. So if you had a 100mm lens at f/4 (100/4=25) this is telling you that the diameter of the aperture is 25mm (1/4 of 100mm).

Ok, so where does the halving doubling come in?

Well when you take in account the AREA of the circle created by the aperture opening you will understand the halving/doubling scenario.

Using the above example (100mm lens at f/4), the area of the circle formed is approx 490mm (Pi X The Radius Squared). Now 100mm lens at f/2 gives us a circle with an area of

[Ronald S. Jr.]

First off, the end looks unfinished. Did you forget to type something?

I'd also like to note that most of the very new cameras (and all 1-series Canon cameras) are capable of displaying aperture, shutter speed, and ISO in 1/3 stop increments. This can still be easy to understand, though. For every 3 clicks of ISO that you change, you need to do the same with your shutter speed (or aperture) to get a proper exposure. No need to memorize what the settings are, or should be, or what number comes after f/2.8. Just remember...3 clicks on one, 3 clicks on the other.

Thanks for the article, Steve.