system is to split the incoming image into three colored images as
efficiently as possible with minimum image distortion. In this system, as
seen in figure 3-1, the primary image from the zoom lens falls directly on
the green tube, because the image does not pass through any additional
glass. Since the wideband signal is taken entirely from the green tube, the
high peaking usually required in video processing is minimized, and signal-
to-noise ratio is minimized.
a. The green light passes through the red/blue reflective layer, which
is deposited on a 1/6-inch thick glass plate, element 1.
introduced by this glass is corrected by element 2, the astigmatic
b. The red and blue light is reflected from the front surface of
element 1, and a red and blue image is focused on the mask and field lens
Light passing through this assembly then hits element 6, the
ultraviolet/infrared stop. Visible red and blue light passes through this
(1) The blue light is reflected to the relay lens and imaged on the
The deastigmatizer, element 5, corrects the astigmatism
introduced by the astigmatic corrector, element 2.
(2) The red relay lens forms the red image on the tube via a front
surface mirror, element 4.
With this system, all of the green light gets to the green tube, all
of the blue to the blue tube, and all of the red to the red tube. Thus, the
light efficiency is as high as possible commensurate with good colorimetry.
The red and blue relay lenses are identical, and each minimizes its
image to 0.75 of the green image height and width. Thus the area covered by
the red and blue images is about one-half of the green area. This has three
very important advantages, as follows:
a. First, the dark current of the red and blue tubes is one-half of
what it would be if the full size raster were scanned.
b. Second, minification is equalization of primarily capacitive
discharge type lag. This type of lag is proportional to the target voltage
Compressing the image onto a smaller scanned area of the tube
increases the target voltage swing, and thus reduces lag.
The result is
minimal differential lag.
c. Third, minification allows normal, zone-3, tube blemishes not to be
seen, because that area is not scanned.
d. This optical system allows the use of light baffles because of its
This prevents any light outside the field of vision
striking the targets.