Let’s Talk Exposure

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.

The Fundamentals

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.

Shutter Speeds

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:

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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.

Exposure Values

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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Ms. R.

About Ms. R.

Danielle Rochford has been a certified teacher for over 15 years, practicing her craft with middle school students in British Columbia, Canada. She is also a self-taught landscape photographer and founder of D-Roc Photography and Design. She has spent the past five years teaching online in such areas as English, Math, and Photography. She hopes to continue sharing her expertise with others now on Udemy. Danielle encourages her students to be interactive and provides many opportunities for discussion and feedback. In her spare time, she loves to travel and enjoy the solitude of nature. You will often find her traveling through Jasper, AB on a photography adventure.

2 thoughts on “Let’s Talk Exposure

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