SECTION 6 - FOCUSING
A. General. The most accurate way to focus a classical lens is to find the exact
center and align the center of the filament to that point. The enormity of the
lens makes this task somewhat difficult. Placement of the filament lower than
desired will cause the light to shine above the horizon. Misalignment along
the optical axis (vertical centerline) will cause a reduction of intensity.
B. Method. Most lenses contain either machine screws or tapped holes inside
the frame at the center of each bull's-eye or center drum section. If screws
are not inserted, determine the tread size and install an appropriate machine
screw or threaded eyebolt into each hole. Attach string to one screw and
span across to the opposite frame. Pull tight enough so that the string will not
sag or be influenced by a string passing over it and secure. Install strings on
all frame rails to insure accurate determination of the center of the lens.
Insert the appropriate focus fixture in the lampchanger. Fixtures for the 250-
watt lamp in the CG-4P are available from Tideland Signal Corporation.
Fixtures for 1000-watt lamp for the CG-2P may be constructed in accordance
with the sketch shown in Figure 6-1:
1/"4" HOLE
1"
1/2"
3"
7/16" HOLES
4"
1/4" WOOD DOWEL
GLUE
ASSEMBLY
7/16" WOOD DOWELS
TOGETHER
1/4"
3/4"
1"
1-1/2"
CG-2P FOCUS FIXTURE
Figure 6-1. 1000 Watt Focus Fixture
Insert the focus fixture into the lampchanger and align the lampchanger so
that the tip of the fixture just touches the intersection of the strings, as shown
in Figure 6-2.
6-1