 |
|
| A B C D E F G H I J K L M N O P Q R S T U V W X Y Z |
|
|
focal length
The distance between a mirror or a lens and its focal point. The focal length of a compound optical system, given as if it were a single optical element, is called the equivalent focal length. The focal length at which an optical system seems to be working in a given situation is known as the effective focal length. For example, if an eyepiece projects an image onto a film, the image is magnified as if it were made by a telescope of several times the telescope's equivalent focal length. The back focal length is the distance between the last surface of a compound optical system and the focal plane of the system and may be quite different from the actual focal length.
Related category
• OPTICS AND OPTICAL PHENOMENA
Also on this site:
Encyclopedia of Alternative Energy & Sustainable Living
Encyclopedia of History
Transport Concepts & Designs (partner site)