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To take a photograph we take an exposure, this means we allow a controlled amount of light onto a sensitive surface. In the old days it was glass plates, then film, now digital sensors. The same concepts of exposure apply to each and to movie film and video, which is only a series of still images recorded.

There are 6 components to the exposure:-

  • the amount of light

  • the sensitivity of the recording device, film, sensor ....

  • the length of time the shutter is open (shutter speed)

  • the size of the hole the light passes through

  • the focal length of the lens

  • the distance from the hole to the recording medium

The last two are often overlooked, and you may like to think of there being the same amount of light but it being spread out thinner over a larger area, or concentrated onto a smaller area. We combine the last three of these together as the Aperture, represented by its own system of F numbers.

So we have reduced this to 4 controllable variables in routine use.

We can vary any of these so as to get the results we require.

We can vary the light by

Change the sensitivity of the recording

  • with digital or video, changing the ISO setting

  • with film (still or movie) putting in a faster or slower film (ASA or ISO)

Changing the shutter speed

  • higher speeds to stop action, and cope with camera shake

  • slower speeds to create blur, moving water effects and the like

  • very slow speeds to record star trails, to take images that moving items are not shown in.

Changing the aperture

  • Smaller hole large F number i.e. f22 has a greater Depth of Field (DOF)

  • larger hole with smaller F number i.e. f2 for a reduced depth of field, for example throwing the background out of focus

To get a fuller understanding of exposure please follow the Exposure Article Route (see below).

   <<  ^  Exposure Article Route   ^  >>    Exposure required and Sunny 16 Rule 

See below for details

Exposure Article Route

The Exposure Article Route takes you through a series of articles relating to exposure and the components of it. Clicking on the << or >> will take you back or forward, the next forward link is also shown. Clicking on either of the ^ symbols will return you to this page.

The route is:-

  1. Exposure

  2. Exposure required and Sunny 16 Rule 

  3. Exposure with an Exposure Meter

  4. Zone Systems Photography  

  5. EV and the EV Table   

  6. Aperture

  7. Shutter Speed

  8. ISO and ASA

  9. Comparative Table of ISO, ASA , DIN and GOST 

See also

Exposure required and sunny 16 rule 

Exposure with an exposure meter

EV table 

Zone systems photography 


Shutter speed  



By: Keith Park   Section: Exposure Key:
Page Ref: Exposure Topic:  Exposure  Last Updated: 08/2009

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