[QuadList] was Cronkite's first half-hour newscast..now camera exposures..now IO tubes

[Dave Sieg]

Been seeing way more than the usual amount of Image Orthicon video with
Cronkite's passing.
Image Orthicons always had a strange look to them. They were much more
light-sensitive than vidicons or plumbicons, due to the way they used
photomultiplier-like secondary emission to amplify the return electrons.
 This gave them a much more logarithmic response, which was hard to tame
with no decent gamma circuits.  As a result,  bright areas easily
overwhelmed the picture.  This also gave them the "dark halo" effect, where
bright areas produced so many electrons they could not all be collected and
"splashed back" onto the target.  Oddly enough, this tended to enhance
perceived sharpness.  You can see this effect on the close-ups of Kennedy's
face in the clip.   Wikipedia says NASA  continued to use IOs to track the
Apollo/Saturn launches for years after the broadcasters abandoned them
because they could pick out details as the rockets neared orbit when nothing
else could.(Excellent writeup on IO theory:
http://en.wikipedia.org/wiki/Image_orthicon_tube#Image_orthicon )

I just remember that they had so many different electrode voltages that had
to be tweaked, each effecting the focus and gamma and even the geometry of
the image, it was infuriating - you could never get it right, just close.
 In the TK-41, focus and deflection coils ran so hot they had to have fans
cooling the tubes. I found this picture in my collection from a 'telethon'
at WKPT in the late sixties, where the lights had been on continuously for
days and the cameras were run with their doors open to keep the tubes from
overheating. You can see the cooling air-hose and one of the IO assemblies.


And we remember these as the good ole days?

-- 
Dave Sieg
http://www.zfx.com
http://www.davesieg.com
http://www.scanimate.net
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