Page 6 - pm_1950_08

Your Laboratory Manager says-

Last month I covered the First Stage of our Reversal Process and left your
film as a negative after the first Development Bath. This negative is, of course,
not fixed out in the hypo bath (this function being carried out at the very end
of Reversal Processing). Thus in the negative the maximum exposed area of
the image is black and the minimum white.
To continue the .process the film is then immersed in a reversal bath which
dissolves the black or exposed particles of silver on the negative image and
leaves a brownish positive image. The next stage is the bleaching bath which
removes this brownish tinge. I should explain that directly after each chemical
bath the film passes through a wash tank which thoroughly washes and removes
surplus traces of chemical.
Next comes the automatic compensation-a controlled fogging-which is
dependent upon the overall density of the image. Simply this means that a very
dim red light is shone through the film on to a photo-electric cell and naturally
the degree of blackness or density of image holds back a certain amount of
light, falling on the cell, in ratio. This cell in turn controls the brilliance of the
fogging lamp, which is situated directly beside the cell. Thus, the less the density
of the image the more the fogging, and vice versa. If your film is correctly
exposed in the camera there is no change in the intensity of this compensating
exposu"re lamp, but if you yourself could stand beside one of our reversal pro-
cessing machines and note the changes that occur to this fogging lamp between
films, · and even between scenes on the same film , you would realise that the
standard of amateur exposure is very variable.
After the compensated exposure comes the Second Development which
blackens the remaining silver halide grains on the positive image. The degree
of development required is dependent upon the amount of the second exposure
which is in turn controlled by the original exposure in the customer's camera. A
well exposed film in the camera will have a fairly high second exposure, and
conversely for an under exposed film. In this latter case only a proportion of
the grains will be developed and the remainder dissolved in the last stage, i.e.
the fixing bath.
Another function of this bath is to harden the emulsion on the film. The
film is finally washed and dried, and is now a complete direct positive.
Before leaving the subject of emulsions, I should explain that the treatment
of SS stock is different from that of VF film. For your own sakes therefore do
not load VF film in SS chargers or vice versa. Quite a few customers have made
this mistake with dire results to their films.
Finally, I would like to say a few words about cameras. So many customers
realising that they have a "movie" camera in their hands insist on moving it
about. I see so many films where the cameraman has literally "sprayed" the
scene with his camera, after the fashion of a hosepipe. Next time you view an
old comedy, or any well made film for that matter, note the minimum amount of
camera action. Keep your camera still until you wish to move it for a definite
purpose. If you desire to "pan" round then do so very slowly and steadily.
T 0 be able to produce good camera work one must be able to appreciate good
camera work, but more will be said about this in my next article.
Page Six