
Eidophor - foo42
https://en.wikipedia.org/wiki/Eidophor
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baobrien
Mike Harrison of mikeselectricstuff gave a talk at the 2016 Hackaday Belgrade
conference on how insanely complex these things were.

[https://www.youtube.com/watch?v=3-BvMcqEc98](https://www.youtube.com/watch?v=3-BvMcqEc98)

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beautifulfreak
He mentions the Eidophor's only competitor, the GE Talaria, which is also
interesting:

[https://en.wikipedia.org/wiki/Talaria_projector](https://en.wikipedia.org/wiki/Talaria_projector)

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avinash
I am quite impressed by the image quality and the sharpness for something that
was used in the 60s. Of course, digital screens are better now but whoever
invented the Eidophor at that time did extremely well.

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acqq
I remember "live" projections of a TV video signal used in BBC programmes in
late seventies, where you see on the stage a huge screen and seemed that it's
not a film projection, and at that time I just couldn't imagine how they
managed to do that, knowing only how the CRTs worked -- and big projections
simply "didn't fit" that model. I considered that a pure magic.

And now searching the internet, they really did have this technology (see the
comments):

[https://hackaday.com/2016/03/15/retrotechtacular-eidophor-
an...](https://hackaday.com/2016/03/15/retrotechtacular-eidophor-an-unknown-
widely-used-projector/)

"When I worked at the BBC West London studios in the 70’s we regularly used
Eidophors for back projection"

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yborg
Fascinating. I always wondered what was used in the 1960s to project the huge
screens in NASA Mission Control.

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amelius
Since it uses a "slowly rotating disk" for the projection, what was the
latency of the technology?

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avian
The rotating disk is only there to replenish and renew the oil surface on
which the electron beam is drawing the image. The speed of disk rotation has
no effect on the latency.

It does have an effect on persistence of the image, but my understanding is
that the disk was slow enough that movement was negligible compared to how
fast the oil deformations faded.

Eidophor has practically zero latency, same as a CRT - whatever the electron
beam draws is immediately visible.

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plutonorm
I wonder if you could do digital holography with this?

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trhway
not sure about holography, i think one can imagine how an electron beam
modulated surface (or may be volume) can say change laser direction thus
providing kind of non-mechanical scanning in a lidar for example. Though it
sounds like a last century approach. These days i'd bet on something like
nanotube channeling the beam and say flexing in response to the field.

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taffer
I wonder what the advantages / disadvantages were compared to CRT projectors
that came out in the 1950s.

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mannykannot
From the article: the Eidophor was 80 times brighter than CRT projectors of
the time.

Presumably because it was a modulator of an independent light source, rather
than the source itself.

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pmcjones
Doug Engelbart's famous 1968 demo used an Eidophor.

