Narrow-bandwidth Television Association
At the Conventions Steve Ostler is always present with his left handed optics
Nipkow type colour camera and monitor. In the past this was a two colour camera
matrixed to obtain RGB signals for the RGB monitor. But Steve wanted more
perfection, so he started work to make an RGB camera. From this work he reported
From Steve Ostler
Now I have installed the disks laser-cut from Denis Asseman's file, here are
some examples of results, taken from the screen of my mechanical colour monitor.
The signal source for most of them was Grant's eprom generator, though one
picture shows Mickey Mouse as seen through my mechanical colour NBTV camera. I
could do with a willing model! In reality the pictures look much better - some
degradation has been caused by the digital photography.
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a discussion group
Enjoyed meeting everybody at Loughborough.
I'm thinking of how I can improve things next year so the monitor can work
in brighter light, and the camera in dimmer light, making things more practical
in the environment we have.
How about this?
Strip out the 'colour' capability from my camera and use the then-unobstructed
photomultiplier to make a very sensitive b/w camera that
I could use in even dim light. A Luxeon to replace the colour mosaic in the
monitor would give brilliant b/w pictures. I'd then have a very sensitive
b/w system giving bright pictures. It would then be simple to modify the current
3D shutter disks for frame-sequential RGB colour. No electronic work necessary
at all! Stereoscopy could be included too.
But to do this I need one thing. I haven't got: a panchromatic
photomultiplier. I've heard they exist. Anyone know where I could get one?
Thanks, Steve Ostler
I've now installed the three new photomultipliers (with colour filters) and
new signal chains into my mechanical colour camera. I'm getting NBTV pictures
in full colour (ie. with all the three primaries correctly
rendered). Thanks to using a panchromatic R446 PMT on the red channel (with
931A's on the rest), red sensitivity is fine. However the old problem is back
- getting all the light evenly spread across the field into all the three
colour channels (R,G,B) at once. The result on the picture is a 'purity error'
with a pronounced yellow cast toward the left.
To pass the light to the PMTs, I'm currently using a single condenser lens
and simple light diffusers. I found this arrangement works the best but it's
also inefficient. It means the camera is insensitive and will only work in
daylight. You'll recall I was having trouble getting adequate sensitivity
and matching evenness of the colour fields with my new 3-photomultiplier camera,
which had replaced my earlier '2½ colour' arrangement seen at the convention;
this used one PMT (blue) and one club cell (red).
I'm pleased to report I've now been offered no less than two dichroic RGB
splitters (ex broadcast tv cameras) from different people, both for free.
Aren't people kind?
I now look forward to mechanically generating really high quality NBTV in
full colour and in quite dim light.
The three colour camera at work
Here are some off-screen photos taken with my new 'improved' (what - again...?
:) NBTV camera and displayed on the separate monitor. Needless to say, trying to
capture the results to do them justice with a digital camera is difficult...
Unlike at the convention, pictures are now in full RGB colour, and (as
before) are using laser-cut 30-line discs with square holes. DC restoration
has now been added (as it should have been long ago!).
The colour separations in the camera are achieved using a dichroic block (taken
from a defunct broadcast tv camera).The three parallel colour channels are all
the red channel. The R446 I am using for the red is physically identical to
the 931A's used in the green and blue, but is red-sensitive. 3D-stereo
colour pictures are still possible using plug-in adapters I made for both
camera and monitor.
Thanks to the efficient dichroic splitter and the use of PMTs, the camera is
very sensitive and indeed gives its best results in subdued room light,
meaning it's now easy to be televised and view the results on the monitor at
the same time. For use in very dark locations, the camera includes its own
auxiliary lighting, mainly consisting of little fluorescent tubes, as can be
seen in the photo.
I hope I can now lay this NBTV obsession to rest - at least until the next
convention ! ;-)