Ultrapurple
Comparison of shadow mask and beam index picture tubes
Most of the world's colour cathode ray tube (CRT) televisions and monitors used a system known as a 'shadow mask' to steer beams from three electron guns to (only) red, green or blue dots of phosphor inside the screen. (Sony's Trinitron used a different gun arrangement and vertical wires rather than a shadow mask, but the principle is comparable).
At the dawn of colour TVs in the 1950s a very few TV tubes were developed using different techniques, including the 'apple' beam index tube (also known as 'Uniray') that used a single electron gun that was switched rapidly between the red, green and blue colour signals as it traversed red, green and blue stripes on the tube face. As there was no shadowmask (which stopped roughly 2/3 of the energy) the beam index tube could be brighter for the same power and even higher resolution. The problem was working out when to switch the beam between the colours. This was generally (and ingeniously) solved by adding a fourth 'colour stripe' - one that emitted only ultraviolet light - and detecting the flashes of UV as the beam passed the UV strip. Various methods were used to detect the UV light.
The only TV sets known to have used a beam index tube are a couple of models from Sony. Then, in the mid-80s, Hitachi decided they wanted to put the world's first colour viewfinder on their camcorder. Beam index tubes were reckoned to have a better resolution and brighter picture than traditional shadow mask - particularly when you're dealing with miniature tubes about an inch and a quarter across - so that's what they went with. The camcorder was sold under various names including Hitachi, RCA (as the RCA CKC021, from which my viewfinder came) and, I think, Sears.
There is a fascinating historical and technical page on beam index tubes at visions4netjournal.com/indextron/ and it includes some photos of the insides of this type of viewfinder. The Wikipedia page en.wikipedia.org/wiki/Beam-index_tube is also worth a look.
These images are mainly for my reference. The shadow mask image was photographed from a Travelvision CT101. Although the beam index image looks dimmer and more dowdy than the shadow mask it's just down to the way the Travelvision was set up (max contrast, max colour) whereas the beam index tube is set up 'properly'.
Photographed with a Nikon D600 modified for wideband response, UV-Nikkor 105mm f/4.5. Baader IR/UV cut filter used for visible light images, Baader 'U' 320-380nm filter for UV images. The images are at the same scale - the beam index tube is smaller than the shadow mask tube. The Travelvision CT101 used a 1.5" shadow mask tube whereas the viewfinder's beam index tube was 1.25".
Oh, and in case you find this because you're looking for pinout details for the viewfinder, thank you for reading this far. The connector is a Hirose CN 508. Pin 3 (orange wire) is video, pin 4 (yellow wire) is +12V ~250mA and pin 7 (white) is ground. (Why they didn't make black ground, red +12V and yellow for video is beyond me - those colours are in the 8-core cable).
Comparison of shadow mask and beam index picture tubes
Most of the world's colour cathode ray tube (CRT) televisions and monitors used a system known as a 'shadow mask' to steer beams from three electron guns to (only) red, green or blue dots of phosphor inside the screen. (Sony's Trinitron used a different gun arrangement and vertical wires rather than a shadow mask, but the principle is comparable).
At the dawn of colour TVs in the 1950s a very few TV tubes were developed using different techniques, including the 'apple' beam index tube (also known as 'Uniray') that used a single electron gun that was switched rapidly between the red, green and blue colour signals as it traversed red, green and blue stripes on the tube face. As there was no shadowmask (which stopped roughly 2/3 of the energy) the beam index tube could be brighter for the same power and even higher resolution. The problem was working out when to switch the beam between the colours. This was generally (and ingeniously) solved by adding a fourth 'colour stripe' - one that emitted only ultraviolet light - and detecting the flashes of UV as the beam passed the UV strip. Various methods were used to detect the UV light.
The only TV sets known to have used a beam index tube are a couple of models from Sony. Then, in the mid-80s, Hitachi decided they wanted to put the world's first colour viewfinder on their camcorder. Beam index tubes were reckoned to have a better resolution and brighter picture than traditional shadow mask - particularly when you're dealing with miniature tubes about an inch and a quarter across - so that's what they went with. The camcorder was sold under various names including Hitachi, RCA (as the RCA CKC021, from which my viewfinder came) and, I think, Sears.
There is a fascinating historical and technical page on beam index tubes at visions4netjournal.com/indextron/ and it includes some photos of the insides of this type of viewfinder. The Wikipedia page en.wikipedia.org/wiki/Beam-index_tube is also worth a look.
These images are mainly for my reference. The shadow mask image was photographed from a Travelvision CT101. Although the beam index image looks dimmer and more dowdy than the shadow mask it's just down to the way the Travelvision was set up (max contrast, max colour) whereas the beam index tube is set up 'properly'.
Photographed with a Nikon D600 modified for wideband response, UV-Nikkor 105mm f/4.5. Baader IR/UV cut filter used for visible light images, Baader 'U' 320-380nm filter for UV images. The images are at the same scale - the beam index tube is smaller than the shadow mask tube. The Travelvision CT101 used a 1.5" shadow mask tube whereas the viewfinder's beam index tube was 1.25".
Oh, and in case you find this because you're looking for pinout details for the viewfinder, thank you for reading this far. The connector is a Hirose CN 508. Pin 3 (orange wire) is video, pin 4 (yellow wire) is +12V ~250mA and pin 7 (white) is ground. (Why they didn't make black ground, red +12V and yellow for video is beyond me - those colours are in the 8-core cable).