The aperture stop of a photographic lens can be adjusted to control the amount of light reaching the film or image sensor. The aperture size regulate the film or image sensor's exposure to light. Lens aperture is usually specified as an f-number, this diagram demonstrates what the f-number actually is, as the f-number increases the diameter of the entrance pupil decreases and as such less light reaches the lens. The size of the aperture stop also affects depth of field, larger f-numbers produce a longer depth of field, allowing objects at a wide range of distance to all be in focus at the same time. [1]
Shutter speed is the length of time a camera's shutter is open when taking a photograph, shutter speed in combination with aperture regulates the film or image sensor's exposure to light. [2] To freeze fast moving objects such as a fast flowing river a very short shutter speed would be used, whereas a very long shutter speed could be used to intentionally blur a moving subject for artistic effect. [3]
ISO
The ISO setting refers to the camera's sensitivity to light, the higher the ISO, the more sensitive it is. ISO is actually measure according to international standards so ISO100 on one camera will be the same as another. ISO increases by doubling the previous ISO, this will also double the camera's sensitivity to light.
This image perfectly shows the ISO scale and when ISO might need to be adjusted. [5]
[1] Gibson, H. Lou. 1975. Close-Up Photography and Photomacrography. 2nd ed. Kodak Publication.
[2] Sidney F. Ray. 2000. Manual of Photography: A Textbook of photographic and Digital Imaging. 9th ed. Focal Press.
[3] Frost, Lee. 2000. The Complete Guide to Night and Low-Light Photography. Amphoto Books.
[4] Stansfield, Andy. 2011. Understanding Exposure The Expanded Guide. Ammonite.
[5] www.digitalcameraworld.com
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