The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Thought Photographing                    Time, Development by
Thought Photographing, See Retinal Impression.
Time, Development by. A system advocated by Mr. Alfred Watkins, who has devised a special clock, the eikronometer, as an aid in the method. The basis of the system is the time of appearance ; the time of appearance being the time elapsing between pouring on and the first appearance on the plate of any trace of the image. It follows then, says Mr. Watkins, that if the plate be always developed for a given multiple of the time of appearance, a standard amount of contrast will always be secured even with changes of temperature or alkali. This multiple is called the multiplying factor.
We may now take a note from Mr. Watkins' latest instructions, as given in The Amateur Photographer for April 12th, 1901.
Procedure. The developer being mixed, place the plate in the dish, and at the moment the hand of your watch touches an even minute, pour on, and rock the dish; the moment the high-lights are first seen on the creamy surface, note the time. The time elapsing between pouring on and first appearance is the time of appear-ance, and this, multiplied by the multiplying factor, gives the total time for development. It is usually convenient to count seconds when you pour on, a half-second chain pendulum (as used in my exposure meter) being a convenient timekeeper, as the beats can be counted by touch without looking at it. Example: The image appears in 45 seconds with a two-grain pyro-soda developer (half grain bromide); five is the factor, and the total development is therefore 3| minutes. If greater con-trast should be wanted, use a factor of, say, seven times ; if a small degree of contrast, as in a snow scene, three and a half times may be enough.
What Developer to Use. It really does not mucji matter, except that those in which density follows detail very quickly should be avoided for half-tone work.
Multiplying Factor. This is the ratio between time of appearance and the attain-ment of a desired amount of contrast between the tones.
The figures given are not a fixed quantity, but are to be varied
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