680 
III. PHOTOGRAPHIC RECORDING 
The camera has the function of recording permanently the movement of 
the spot on the cathode-ray tube. In some cases the spot movement contains 
the time base as well as the desired signal, For this type of record a 
camera with cut film or 35-mm film may be used in the conventional manner. 
In other types of recording, the time base is supplied by the movement of 
the film, and a rotating-drum or streak-film camera is used. 
The operation of all cameras involves the following components: a 
hood to keep out stray light, a lens and shutter combination, a film back, 
film, and lastly a means of viewing the object photographed. The units used 
on a DuMont type 208 oscillograph are shown in Figs. 19 and 20, 
For recording several channels on a single film special camera hoods 
are constructed to take the standard camera backs and film holders, 
The standard hood is hinged at both front and rear for inspection of 
the cathode-ray tube screen. Inside the hood is a manually operated shutter 
and on top is a viewing hole with prism. The section that swings open holds 
a lens (f/2.0, focal length 50 mm), a Wollensak shutter, and clamps to hold 
any of the three standard film backs, The cut-film back takes a standard 
6s x 9 cm film holder, and gives four exposures as the back is removed and 
rotated, The roll-film back contains a rebuilt Argus camera which gives ex-~ 
posures on 35-mm film. The rotating-drum back carrics approximately 10 
in, of 35~mm film and may be driven from a constant-speed motor, either by 
a flexible-shaft drive or by a pully drive. 
The film used is not extremely critical, but the best records have been 
obtained with Eastman Fluorographic film. A typical development uses D-19 
for 6 min at 18°C, It has been found that an increase in time or temperature 
will raise the background fog more than would normally be expected. Other 
fast films and contrasty developers have been used with almost equivalent 
results, 
Using this equipment, it has been routine to photograph with good reada- 
bility a single trace in the form of an exponential pulse with a time con- 
stant of 50 msec, which crosses a 5-in, cathode-ray tube sercen, in 1 msec. 
7 ————_———- 
—‘Accelerating potential and intensifier electrode potentials each 
1100 volts. 
shia 
