Article: Best viewing distance for photographers. (determining at what distance a photograph should be viewed)

Article: Photographic lenses. (usage tips and focal length ...
PSA Journal;  July 1, 1992 ;     700+ words ...The focal length needed to cover a given negative can ... the negative = 6.4 inches. Lens focal length are always expressed in metric measure ... aperture designations are related to the focal length of the lens. If we could get inside ...

Article: Focal length variability and protein leakage as ...
Photochemistry and Photobiology;  July 1, 2003 ;     700+ words ... ... monitor lens damage: (1) measuring focal length variability using a ScanTox(TM) instrument ... damage to the lens, we also measured the focal length variability and protein leakage induced ... correlated (r = 0.9) with variability in focal length. Lenses treated with hypericin and ...

Dictionary definition: effective focal length
A Dictionary of Astronomy;      298 words ...effective focal length The focal length at which an optical system appears to be working. For example ... produced by a telescope of several times the telescope's actual focal length. The magnification is given by ( d / F ) - 1, where d is ...

Article: Japanese Inventor Develops Focal Length Measuring ...
US Fed News Service, Including US State News;  September 20, 2006 ;     512 words ... ... Namiki of Hanno, Japan, has developed a focal length measuring device for measuring a focal length of an optical system. According to the ... Patent & Trademark Office: "A focal length measuring device comprises a light source ...

Dictionary definition: focal length
A Dictionary of Astronomy;      253 words ...focal length (symbol F or f  ). The distance between a lens or mirror and its focal point. Together with the aperture, the focal length is one of the main properties of a lens or mirror. The longer the focal length, the larger the image scale.

Dictionary definition: equivalent focal length
A Dictionary of Astronomy;      262 words ...equivalent focal length The focal length of an optical system expressed as if it consisted of a single optical element. It is used to describe the focal length of an enclosed optical system, such as an eyepiece, which has no position from which the focal distance can be measured.

Article: Taiwanese Inventors Develop Reflector with Negative Focal ...
US Fed News Service, Including US State News;  May 26, 2007 ;     563 words ... ... luminaire with reflector of negative focal length. According to the U.S. Patent ... luminaire with reflector of negative focal length is disclosed, which comprises a light ... screen having a reflector of negative focal length, a side screen and a plate; wherein ...