In setting the copyboard counters to the principal lens, it is only
c. Copyboard Setting. The copyboard, like the lensboard, is
necessary to determine accurately the distance between the
positioned to counter readings calculated to the principal lens,
focusing glass. and the copyboard, as shown in figure 5-2, and
and requires a corrective constant for the secondary lens. This
then set the counters to agree with this distance plus the nodal
constant has been added or subtracted to all copyboard
correction for the lens. This nodal correction is approximately 3
readings on the focusing chart of the secondary lens. The
/ 2 the nodal separation, and can be used to add to the
constant is a difference of the nodal separations between the
measured distance to set the counters. If a long trammel rod is
two lenses and can be positive or negative depending on
not available, double trammeling with a shorter rod can be used
whether that of a secondary lens is a greater or lesser distance
to determine the overall distance, by adding the focusing glass-
than that of the principal one. The copyboard readings for the
to-lens-board distance (plus the nodal correction) to obtain the
principal lens on the focusing chart (to which the counters are to
copyboard counter readings for the principal lens.
agree) represent the overall optical distance from the inside
surface of the focusing glass to the surface of thecopyboard.
Figure 5-2. Trammeling focusing glass and copyboard.
lamps, switch on copyboard turbo-compressor, and obtain the
d. Optical Check of Accuracy of Counter. After adjusting the
test chart, a drop cloth (to block out extraneous light if the
counters to agree with lensboard and copyboard readings on
camera is to be tested in the open instead of the darkroom),
the focusing chart (for the principal lens), the camera must be
and a focusing magnifier provided with material and supplies
checked optically to ascertain that the use of the chart will
accompanying the camera issue. The camera is checked as
provide exact reproduction size and focus. For this purpose a
follows:
test chart is furnished with the camera, and consists of a grid of
lines printed onto a white lacquered metal plate, this grid being
(1) Measure overall thickness of copy. Then mount
identical to that on the focusing glass. By choosing appropriate
copy on copyboard, centrally and square.
rectangles on this grid, such as the 10,000 inch square and
(2) Position copyboard to same-size counter
20,000 inch square, and projecting their image on to the
reading on chart plus copy thickness in hundreds of an inch.
focusing glass, a means for accurately determining the
correctness of ratio counter readings, as well as sharpness of
(3) Mount lens, open diaphragm up to f:16, and
focus and parallelism between the copyboard and focusing
position lensboard to same-size (focusing chart) counter
glass throughout its range of movement, is available. To
reading.
perform the optical tests, put camera into operating condition,
making electrical connections, trim carbons and position arc
5-5
