This resource is designed to help convey the concept of depth-of-field in photography.
A number of factors influence how much of an image will be considered to be in focus. However, this resource deals with one of the main variables a photographer can use to control depth-of-field - namely aperture.
In the interactive resource, the user can select from different aperture settings with one-stop variations. Clicking on a given aperture will result in the main background photograph altering to represent the image that would result from choosing the selected aperture.
This is supported with a cross-section diagram of a DSLR camera showing two points of reflected light captured - one from where the focus has been achieved and the other towards the rear of the image. These are represented by two different shades of coloured triangles passing through the aperture and the lens, then being projected onto the sensor at the back of the camera.
At the smallest aperture (f/22) the circle of confusion causes the end of the subject to appear to be in focus, whereas, at a wider aperture, the end of subject is outside the circle of confusion, therefore appearing to be out-of-focus.
The depth-of-field is represented by a tinted rectangle so the user can grasp the concept of a reducing depth-of-field as the aperture increases in size (counter-intuitively small f-numbers) and a wider depth-of-field as the aperture is decreased (larger f-numbers).
The resource will also display the reciprocal value for the shutter-speed in order to maintain the chosen exposure.