Exposure can be defined as the amount of light reaching a photographic film or sensor, as determined by shutter speed, lens aperture, and scene luminance. Being able to expose a scene properly requires calculating how much light reaches the image sensor or film with accuracy. If there is too little exposure then the image will be too dark, but if there is too much exposure then the image will be too light. There are two factors that control exposure. The lens aperture and the shutter speed must be used in combination to attain the right balance and give the end result of a well exposed image.
As I mentioned earlier, the two main factors in determining the exposure are the aperture and the shutter speed. Before we delve deeper into these two factors, let’s cover a few important points. The basic unit of exposure is usually referred to as a stop. One stop is equivalent to a doubling or halving of an exposure (depending on the direction you go). So, the difference between an exposure of 1 second and 2 seconds is one stop. Let’s take a closer look at shutter speed and aperture to try and understand this concept a little better.
Being able to understand how shutter speeds work tends to be a little easier for most people than aperture, so let’s start here. Most exposures require shutter speeds that only last a fraction of a second (although night photography can sometimes involve shutter speeds of seconds, minutes, or even hours!)
Below is a list of common shutter speeds:
There is no hard and fast rule that helps to determine what shutter speed is best to use for a particular subject. However, there are some recommendations that you could use to help make your decision. I speak about them in my post called, “Which Shutter Speed?”
When you decide to take handheld pictures, there is a general rule to remember about shutter speeds:
Always keep the shutter speed to above whatever the reciprocal of the lens’s focal length is.
For example, when you shoot with a 300mm lens, make sure that the shutter speed stays above 1/300.
A correct exposure can be reached by a number of combinations of aperture and shutter speed. For example, if 1/60 sec at f/4 gives the correct exposure, it is also possible to use 1/125 at f/2.8 and have the same amount of light reach the sensor. All combinations of aperture and shutter speed have what is known as an Exposure Value, or EV.
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