THE II. S. OR UNIFORM SYSTEM It will be necessary here to give an explana tion of the Uniform System for numbering diaphragms for the reason that this method is the one now in use on the majority of double lenses in the United States, where, until recently, lens makers employed it in marking their lenses.
This system was originally recommended by the Royal Photographic Society of Great Britain which body later discarded it in favor of the f system which at the present time is quite gen erally used throughout the world.
The Uniform System numerically is just the reverse of a cone unit system since its numbers are proportional to the time of exposure required by each opening, beginning with 1 which is the equivalent of f / 4, as will be seen in the table which follows. This system was a failure in that it was an attempt to do too much, i.e., to furnish a series of relative exposure numbers already worked out for each opening in the lens instead of giving to each opening a number, as does the unit system here recommended, indicative of its true working power or solid angle, leaving the operator free to exercise his reason in solving exposure problems as simple matters of cause and effect.
The author is convinced that less than ten per cent of those who use either the f or the uniform systems of diaphragm markings are aware of the derivation of the terms employed. Practically none use the scales in a purely mathematical sense but arrive at a certain pro ficiency through experience, having learned that each opening requires double the time of ex posure that the next larger one does. state of accuracy could be reached as well should the diaphragms be lettered instead of numbered and I have read that some authorities have been of the opinion that the letters would be much simpler in practice than numbers, since the rela tive working speed could be known and utilized as well and the numbers would cease to confuse those who did not know their derivation nor comprehend their meaning.