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Your Laboratory Manage1· says-

Having given a brief resume on the correct use of V.F. Panchromatic film
and f numbers (aperture stops) in my previous articles, I now wish to dwell upon
a slightly more technical matter-Light Sensitive Materials-or, more generally
"Your Camera Film". This is not intended to be a complete and thorough
article on this subject, but merely a few points which may prove of interest to
all amateur cinematographers. .
LiClht Sensitive Materials - that is a simple description of your charger of
cine film. It is now generally known that all camera film, at present issued by
these laboratories, is of the reversal type. This means that the .positive film
which you eventually project upon the screen is exactly the same film as exposed
by you in your camera. Let us now analyse this cinematographic medium.
Cine film consists of a non inflammable transparent safety b>ase made of
cellulose acetate. Upon this base is sprayed the emulsion, which is a solution
of silver bromide and iodide particles suspended (or contained) in gelatine. At
this point I should say that there is an anti-halation backing between the base
and the emulsion, but more will be said about this later. Before spraying is
commenced, the emulsion or solution is subjected to control by the manufacturers'
trade processes. This controlling has a direct bearing on the speed of the
emulsion-speed being defined as the degree of ability of the emulsion to record
physically the presence of a standard light source. When the light sensitive
emulsion is subjected to light or, alternativelv, exposed in vour camera. a physical
reaction takes place in the minute silver halide grains. The resultant effect -
known as the latent image - is primarily invisible until the film is immersed in a
developing solution. This solution converts the areas of the latent image, which
have reacted under the exposure to lit:1ht, into black formations. The degree of
blackness is entirely dependent upon the degree of liqht falling on the emulsion.
Thus you obtain tones and gradations of light and shade.
The image, in its present form, is now defined as a negative, that is to say,
the points or a,reas reflecting light in the subject photographed are now points
or areas of blackness upon your film and vice versa. This state represents Stage
I of the Reversal Process. Details of Stage 2 in the process will be given in
next month's Pathescope Monthly.
Let us return now to the question of film emulsions. On all emulsions the
silver particles, or "grain", are of crysfal structure and vary in diameter from
0.1 u to Su (I u being a thousandth part of a millimetre). When a fast film (e.g.
V.F. Panchromatic) is required the size of the individual silver particles is
increased. The antihalation backing, referred to earlier, consists of a soluble
material which, during one stage of reversal processinQ, is rendered' transparent.
The function of this backing is to eliminate halation or, the spreading of light from
a liaht area of the image to a darker area due to reflection from the film ba•e.
The foreqoing notes, I feel, are sufficient for the oresent, but more will be
said upon this very important subject in future issues of this magazine.
Club Notes
A cordial welcome will be extended to all visitors to Germany at the Deutscher
Q.Smm. Schmallfilm Club, Bre'men, 8, Zwinglistrasse 76.
The Cameo 9.5mm. Cine Club is a new organisation which has already had
some successful meetings. Anyone interested who is resident in the district is
invited to write to :-
Mr. T. A. Siddons, Stanlev House, 34 Mary Street,
Harpurhey, Manchester, 9.
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