settings if necessary to re-make negatives. Switch off arc
indistinct, reverse switch direction and obtain a sharp image.
lamps and shutter.
(If a sharp image cannot be obtained by lensboard movement
alone, this is usually due to the copyboard being too close the
(7) Close lens diaphragm down to the stop
Move the copyboard away (increasing
required for photography (see TM 5-245).
counter numbers) a few in., and repeat the focusing
g. Vacuum Back Settings and Film Placement.
movements with the lens until a sharp image is obtained.
(1) Set the vacuum back valve handle (13, fig. 1-
(6) Check image size by scale or against the grid
markings on the focusing glass. If smaller than required,
Turn on the vacuum back toggle switch (6, fig.
move lensboard forward a short distance (away from focusing
glass, counter numbers increasing), and adjust copyboard
position until sharp focus is again obtained. Check size of
(3) Place film on the vacuum back, as shown in
image again. Then repeat operations until exact size and
figure 2-14, being certain that film
is held flat and
focus is obtained. During the final focusing, make certain that
In placing film, hold it by edges only. Align one edge with
image is square and centered with the grid on the focusing
rectangle line on the porous plate, and roll the film slightly so
glass (use the oscillating knob (3, fig. 2-4) if necessary to
that it gradually adheres across its length or width to avoid
square, and control knobs (5 and 10, fig. 1-4) to center), and
formation of wrinkles. If it is necessary to shift location,4to
that image is critically sharp when viewed through the
not attempt to slide film, but raise it almost entirely away;
focusing magnifier. Record the carriage readings on the back
relocate and lower it again into contact. Be sure that the film's
or margin of the copy or on an improvised focusing chart to
lighter colored emulsion side is facing the camera's lens. Film
enable return to the same camera
used should coincide with job requirements for continuous
tone or line copy work. (For more detailed information on
films and their characteristics see TM 5-245).