Easel is a device to hold photographic paper flat during exposure, usually equipped with an adjustable metal mask for framing. Eastman, George 1854-1932.
Eberhard effect is a border effect occurring in a developed image.
It appears as a dense line along an edge of high density and as a light line along an edge of low density. It occurs most often in plates developed flat in solution that is not sufficiently agitated. The effect was described by Gistav Eberhard in 1926. Edge numbers are reference numbers printed by light at regular intervals along the edge of 35mm and roll films during manufacture. Effective aperture is the diameter of the bundle of light rays striking the first lens element that actually pass through the lens at any given diaphragm setting.