by the lens is equal to the angle a d b, which may be measured by laying a protractor on it and reading off the degrees included. For those who may not have a protractor handy, the diagram, fig. I, is given, which may be copied on a lantern plate, and the developed, fixed and varnished negative used as a protractor.
To determine experimentally the angle of view included by any lens, fix the lens on a large camera and plot out the angle subtended by the illuminated circle. This can be done as directed in the article Focal Length, under the subsection Grubb's Method. In a similar way the angle of view which any lens includes on a given plate may be determined if the longer side of the plate is set off on the ground glass, and Grubb's diagram is made as directed.
Angle, Wide. Applied to certain forms of lenses which embrace a larger amount of view than the usual run of lenses. Wide-angle lenses exaggerate perspective most painfully, in increasing the apparent size of near objects entirely out of all
proportion with those more distant, unless the photograph is viewed from a point corresponding to the focus of the lens used - a course more practicable as an experiment than as a means of looking with ease at the photograph. As the angle of view of the human eye in ordinary clear,vision does not exceed about