Back to Basics: Understanding Exposure


exposureI’m not sure how it happened, but my posts over the last few months have grown incredibly nerdy.  I mean, for the select few of you out there that have an interest in creating equirectangular photos, reading up on virtual 3D environments, or shooting your listings PAP style, I hope I’ve helped surface some of the newest things happening in the world of advanced photography.  I realize, however, that not everyone is ready to tackle such complex procedures. So if it’s time to break things down for simplicity’s sake, let’s really break it down, and discuss the very root of photography: exposure.

The whole concept of exposure is based on one thing: light.  Essentially, when you use a camera you are capturing light – capture too much light and you overexpose your image, capture too little and you underexpose.  Sound pretty logical so far?  Great.  Most cameras, except for basic point-and-shoots, will allow you to manually control your exposure, and therefore control the light being captured.

Exposing a photograph depends on three, in-camera variables: Aperture, Shutter Speed, and ISO.  That’s it.  If you fully understand each of these variables, and how they interplay, you will be able to approach almost every shooting situation confidently. So let’s have a closer look:

1) Aperture
.  A camera’s aperture is located in the lens.  Think of it as a flexible gateway that can be opened or closed by the photographer to control the amount of light entering the camera.  Aperture size is generally expressed as an f-number (i.e. f2.8).  Historically, the f-number was calculated by dividing the focal length of a lens by the diameter of the aperture.  For instance, if you had a 50mm lens and your aperture measured 25mm in diameter, your f-number would be f2.0 (50 ÷ 25 = 2).  As cameras and lenses evolved, this equation became slightly more complex, but the same general rules apply.  In short, the lower the f-number, the more light you are letting through the lens.  Here’s a basic overview of how aperture works:


2) Shutter Speed: Once the light has passed through the aperture it enters the main camera body.  Before the light is exposed, the mirror must flip up (in DSLR cameras only), and a shutter curtain must open for a precise amount of time.  The shutter may remain open anywhere from a fraction of a second to several minutes (or even hours) depending on the type of shot the photographer intends to capture.  Shutter speeds are usually displayed as fractions (i.e. 1/250 second, 1/1000 second, 1/15 second etc.) or as whole numbers (i.e. 3 seconds, 30 seconds etc.).  Here’s a brief diagram for how shutter speed works:

Shutter Speed

3) ISO: Finally, the light is able to hit the sensor so the prescribed exposure can take place.  Even here though, the photographer can control exposure by controlling the ISO.  ISO is an abbreviated term used in photography to describe how sensitive a roll of film or digital sensor is to light.  ISO increments commonly range between 100 and 3200 but can go higher and lower in some cameras.  The lower the ISO is set, the less sensitive your camera will be to light, and vise versa.  Here’s a basic overview:


A properly exposed photograph relies entirely on a perfect balance between these three variables.  Different shooting scenarios each require a different combination of Aperture, Shutter Speed, and ISO.  You can tell when you are set up properly when your light meter states that you are at 0.0 (the perfect exposure).  That being said, certain settings can have great advantages, or debilitating disadvantages to the final look of your photo.  Next time, I’ll run through some sample real estate scenarios and discuss the best ways to expose them, as well as some things to avoid whenever possible.

Darn.  That post ended up being just as nerdy as the last few.  Maybe next time…

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