Movie theaters c.1940 - using 'electronic' projectors [repost]

Just for fun.
http://groups.google.com/group/alt.t...dd4812 2054f3

Anyone out there still using their venerable 1946 RCA RPTV? ;-)

"David" wrote in message
...
Just for fun.
http://groups.google.com/group/alt.t...dd4812 2054f3

Anyone out there still using their venerable 1946 RCA RPTV? ;-)

Pretty amazing technologies mentioned in that thread. But with that RCA one
(the first one linked)... wouldn't there be a spot left in the centre of the
screen, where the CRT gets in the way? Or could the lens and mirror get
around it, so to speak?

LH

"Luke Hooft" wrote in message
...
"David" wrote in message
...
Just for fun.
http://groups.google.com/group/alt.t...dd4812 2054f3

Anyone out there still using their venerable 1946 RCA RPTV? ;-)

Pretty amazing technologies mentioned in that thread. But with that RCA
one (the first one linked)... wouldn't there be a spot left in the centre
of the screen, where the CRT gets in the way? Or could the lens and mirror
get around it, so to speak?

I thought those kind of TV projector things used mirrors which rotated.


LH

"Agamemnon" wrote in message
...

I thought those kind of TV projector things used mirrors which rotated.

The one I'm talking about doesn't seem to (this one:
http://www.earlytelevision.org/rca_theater.html)

The mirror reflects the image ofn the CRT back through the lens, but the CRT
is poking through a hole in the centre of the lens, and I'm not sure if it
would create some kind of "blind spot".

Some of the other links in that thread talk about projectors with rotating
mirrors and films of oil over glass plates and all kinds of stuff.

LH

Luke Hooft wrote:
"Agamemnon" wrote in message
...

The one I'm talking about doesn't seem to (this one:
http://www.earlytelevision.org/rca_theater.html)

The mirror reflects the image ofn the CRT back through the lens, but the CRT
is poking through a hole in the centre of the lens, and I'm not sure if it
would create some kind of "blind spot".

Take a look at a Celestron telescope. It has a mirror in the center of
the objective lens to fold the optical path back along the optical
axis. The mirror is so far from the focal plane of the lens (out in
space) that it is invisibile when looking through the eyepiece. The
same principle applies here. The CRT is so far from the focal plane in
the field, at the projection screen, that it does not interfere with
the image.

In article ,
Luke Hooft wrote:
Some of the other links in that thread talk about projectors with
rotating mirrors and films of oil over glass plates and all kinds of
stuff.

The oil over glass thingies were (are?) eidophors and the results stunning.
I remember being most impressed with a cinema sized projection of HDTV at
an IBC in Brighton some 20 years ago. But their cost was horrendous.

--
*Artificial Intelligence is no match for Natural Stupidity *

Dave Plowman London SW
To e-mail, change noise into sound.

The message
from "Luke Hooft" contains these words:

"Agamemnon" wrote in message
...

I thought those kind of TV projector things used mirrors which rotated.

The one I'm talking about doesn't seem to (this one:
http://www.earlytelevision.org/rca_theater.html)

The mirror reflects the image ofn the CRT back through the lens, but
the CRT
is poking through a hole in the centre of the lens, and I'm not sure if it
would create some kind of "blind spot".

It won't. All that happens is that the obstruction increases the F stop
number slightly giving a slightly reduced brightness over all of the
projected image.

Some of the other links in that thread talk about projectors with rotating
mirrors and films of oil over glass plates and all kinds of stuff.

LH

--
Regards, John.

Please remove the "ohggcyht" before replying.
The address has been munged to reject Spam-bots.

Johnny B Good wrote:
The message
from "Luke Hooft" contains these words:

The mirror reflects the image ofn the CRT back through the lens, but
the CRT
is poking through a hole in the centre of the lens, and I'm not sure if it
would create some kind of "blind spot".

It won't. All that happens is that the obstruction increases the F stop
number slightly giving a slightly reduced brightness over all of the
projected image.

Ah, thanks, that makes sense. It had to have some negative impact.

As an aside, do you know of anywhere on the web which has info on optics
which explains the science without being overly simplistic?

--
Michael
m r o z a t u k g a t e w a y d o t n e t

"Luke Hooft" wrote in message
...
"David" wrote in message
...
Just for fun.
http://groups.google.com/group/alt.t...dd4812 2054f3

Anyone out there still using their venerable 1946 RCA RPTV? ;-)

Pretty amazing technologies mentioned in that thread. But with that RCA
one (the first one linked)... wouldn't there be a spot left in the centre
of the screen, where the CRT gets in the way? Or could the lens and mirror
get around it, so to speak?

LH

Yup, See the picture of the old "Test pattern on 15 x 20 foot screen". The
black spot in the middle!

j/k.... good question though, it does look to be an issue.

David wrote:
"Luke Hooft" wrote in message
...
"David" wrote in message
...
Just for fun.
http://groups.google.com/group/alt.t...dd4812 2054f3

Anyone out there still using their venerable 1946 RCA RPTV? ;-)

Pretty amazing technologies mentioned in that thread. But with that RCA
one (the first one linked)... wouldn't there be a spot left in the centre
of the screen, where the CRT gets in the way? Or could the lens and mirror
get around it, so to speak?

LH

Yup, See the picture of the old "Test pattern on 15 x 20 foot screen". The
black spot in the middle!

j/k.... good question though, it does look to be an issue.

Take a look at a Celestron telescope. It has a mirror in the center of
the objective lens to fold the optical path back along the optical
axis. The mirror is so far from the focal plane of the lens (out in
space) that it is invisibile when looking through the eyepiece. The
same principle applies here. The CRT is so far from the focal plane in
the field, at the projection screen, that it does not interfere with
the image.

A lens of this type is called "catadioptric".

As a side issue, a German lens company made view camera lenses back in
the forties that had a threaded socket in them, on the optical axis, to
receive a black disk. For female portraiture the disk was screwed in,
providing a flattering diffusion, not unlike a fog filter today.