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Exposure

Rusty on the beachTo discuss Exposure means that there has to be some over-lapping with topics such as Aperture, Shutter Speed, ISO and Depth of Field. They are all closely linked and to adjust the settings of one directly affects the settings of another.

Exposure is the combination of Shutter Speed and Aperture that allows enough light through the lens onto the film/or camera sensor to allow a photograph be recorded in faithful detail.

Shutter Speed is the length of time the shutter opens to allow light into the film/sensor while taking a photograph. The faster the shutter speed setting, the smaller (or more open) the aperture number has to be.

Aperture, then, is the device that controls the amount of light that gets through to the film/sensor. The larger the number (ie. F22), the smaller the amount of light that is allowed through. This can also be described as the F-stop.

ISO Rating is a film term and describes how sensitive the film is to light. In digital terms it describes a rough approximation of film sensitivity.

Depth of field is the amount of the photograph that is in focus in front of and behind the point you have focused on in the picture and is directly affected by the settings of any/all of the above. Confused yet? Don’t be – it sounds more confusing than it actually is.

A large Aperture (F-stop eg. F22) means that the Shutter Speed has to be slower to compensate. In other words the shutter has to stay open for longer. Remember, a large Aperture number = small amount of light allowed through.

A large Aperture (eg. F11 or F22) means that there will be a large Depth of field in the photograph. Meaning that if you focus the lens on a subject, there will be a lot of the picture in focus in front of and behind the subject (see below).

Under Exposed  
Over Exposed
Under Exposed
 
Over Exposed

 

Also if you use a small Aperture (eg. F2.8) there will only be the subject in focus and the background will be blurred.

You may have heard of the term “to bracket your exposure”. This means to take several photos adjusting the exposure settings above and below the meter reading settings. For example, if the camera’s meter says 250th/sec at F.5.6, you would take a number of photos above (250th/sec at F.8, 250th/sec at F.11) and below (250th/sec at F.4 and 250th/sec at F.2.8). It’s worth noting that you can change the shutter speed instead of the aperture to achieve the same result as above. And also, most modern cameras now increase shutterspeed/aperture settings in one third or one half a stop increments.

Modern colour negative film can withstand 1-2 stops underexposure that can be corrected at the printing stage. Transparency film (Slide film) is much more sensitive and has to be exposed correctly (see Film processing). And almost anything is possible on a computer with a digital image!

As you can see this gives you an enormous amount of creative control over the photograph you are taking. And all of these can be used to create very different types of photographs.

Related Articles;

Shutter Speed

ISO Rating

Depth of Field

Film Processing