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COMMITTEE REPORTS
REPORT OF CAMERA COMMITTEE
YOUR Committee has had for consideration but one question of standardization, since the last Fall meeting at Buffalo: this
had to do with the proposal for standardizing the dimensions of the core for negative raw stock.
The principal dimensions which were recommended are as follows :
Outside Diameter: 1 29/32";
Spindle Hole: 21/64";
Slot: M";
Flat on core Outside Diameter, at center: 1 7/8".
The matter was referred to, and is now in the hands of the Standards Committee, for investigation and action. Proposed Standardizing of Speed Markings of Photographic Lenses:
Because of the difficulties which have been experienced in the past in obtaining uniformity of results in the use of present-day "F" values indicated on the principal makes of photographic lenses, a communication was addressed to the Bureau of Standards, Washington, D.C., calling attention to existing irregularities and suggesting that the Department assign someone to the task of studying the matter for the purpose of evolving some standard.
Some of the irregularities pointed out were :
(1) None of the lens makers in this or foreign countries have adopted uniform values corresponding with the "F" number used; that is, no two lenses of the same focal length will furnish the same efficiency at a given diaphragm opening;
(2) The above is true even of any two lenses made by the same manufacturer;
(3) It is also true that no uniformity exists in the values indicated on lenses of various foci; for example: a 50 m/m lens working at F-5.6 seldom produces the same efficiency of a 75 m/m lens working at the same speed — with light conditions and other factors being equal for the test.
A reply, received from Mr. F. C. Brown, Acting Director, is suggestive of co-operation which might be anticipated from the Bureau. In part his letter reads :
"2. As you know, the efficiency of a photographic lens in transmitting light to the film depends upon at least three factors. The F-number, the amount of light lost by reflection at the various surfaces, and the loss of light by absorption. Of these three, the first is generally considered to be the most significant. The
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