Jelaskan dimana: dari Lingkaran gamang

S adalah jarak subyek (en:focal distance)

Thomas R. Dallmeyer pada tahun 1892 mengembangkan pamflet ayahnya, John Henry Dallmeyer yang diterbitkan pada tahun 1874 On the Choice and Use of Photographic Lenses (tampaknya juga mengutip karya J.H.D. On the Use of Diaphragms or Stops) mengatakan:

"Thus every point in an object out of focus is represented in the picture by a disc, or circle of confusion, the size of which is proportionate to the aperture in relation to the focus of the lens employed. If a point in the object is 1/100 of an inch out of focus, it will be represented by a circle of confusion measuring but 1/100 part of the aperture of the lens."

Pada tahun 1889, Edward John Wall pada bukunya A Dictionary of Photography for the Amateur and Professional Photographer'' mengatakan:

To find how quickly a shutter must act to take an object in motion that there may be a circle of confusion less than 1/100in. in diameter, divide the distance of the object by 100 times the focus of the lens, and divide the rapidity of motion of object in inches per second by the results, when you have the longest duration of exposure in fraction of a second.