The SC4020's speed came from the charactron tube developed by Convair in 1948. Wide charactron tubes were the main interactive displays in the US SAGE system air defense system. A mask is placed in the charactron tube, usually shaped like the characters of the alphabet. The beam is extruded through the mask, taking on the appearance of the character, on its way to the tube face. In consequence, characters can be displayed at high speed. The most accurate part of the display is in the centre of the tube. So the version used in the SC4020 has only a 5in diameter and the tube length is several feet.
Charactron Tube
The contents of the charactron mask are:
0 1 2 3 4 5 6 7
8 9 ∂ = " ' δ α
+ A B C D E F G
H I π • ) β ± ?
- J K L M N O P
Q R . $ * γ ∼ d
/ S T U V W X
Y Z ° , ( ∫ Σ □
The quality and the speed of the display were the upsides for animation. The downsides were:
- The original camera was a 35mm one and most organisations only had 16mm projectors unless they visited a cinema
- The character sizes were ideal for microfilm use but almost useless for animation as being too small
- The maximum length of a vector was 64 address points in the X and Y directions out of the 1024 available
- The bluish white phosphor of the tube gave excellent fine lines for black and white film production but emitted little light in the red/green part of the spectrum so colour production was impossible
Charactron Pioneers