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414 AYLING October
A masking shutter is provided for stripping a spot horizontally when desired. The shutter blades are adjustable to compensate for offnormal projection that might occur. In the closed position the shutter can also serve as a dowser. Both the aperture and masking shutter are constructed of Vs-mch brass with a nickel plating to withstand the intense heat to which they are subjected.
The optical-system housing can be removed with very little effort, simply by loosening the three knurled screws holding the housing to the lamphouse, and the single knurled screw, securing the forward end. A lens-access hole is located conveniently to allow cleaning of the lenses without disassembling.
COLOR BOOMERANG
The boomerang is equipped with six color filter slides and a special track for inserting an ultraviolet (black-light-type) filter.
The operation of the individual color filter is accomplished by manually lifting the desired handle to the uppermost position. A permanent magnet located in the top of the boomerang holds the filter securely in position. The color is released by gently pushing the handle downward until it disengages from the magnet, and letting it fall in place. The color slides are easily removable for inserting new colors.
OPTICAL-SYSTEM CALCULATIONS The basis for the optical system calculations is the lens formula1
= + (l)
/ w V
f = focal length of lens
where u = object distance
V = image distance.
Substituting in (1) for the small lens we find that as HI is smaller than /i, for this case, FI is a virtual image, so the sign becomes negative. Therefore,
l-l _JL
/i Mi"1" -Fi
To calculate the large lens position, we know that u2 is tn"e object distance (Fig. 5). So from (1)
L ._ I . J_
f* uz T V,
or m = ~^j. (3)