Nipkow Disk
en.wikipedia.org
en.wikipedia.org
I just fell down the rabbit hole of Broadcast Mechanical Television... very interesting stuff!
I’m still not quite sure how the broadcast tech worked for the individual scan lines - I wonder if it was similar to later TV signals, or completely different?
It seemed odd not to use a rotating cylinder rather than a disc, for parallel rather than curved scan lines. The cylinder could have become a tape, which would have reduced the size of the apparatus, although not as sturdy. /end steampunk mad inventor daydream
You need to create a literal shell of LEDs: a spiral of semicircles which grow larger as you move out and around the spiral. So you start with a 1 cm diameter semicircle strip, with each end of the strip mounted on the axis. Then rotate around the axis by 1°, and add a 1.1 cm diameter strip, and repeat. You end up with a surface that looks like a shell you would find on the beach.
This shell surface, when rotated on its axis, sweeps the entire volume of a sphere, with each LED strip sweeping a fixed radius from the axis. The strips are offset along the curve of rotation to ensure that the eye can see every layer as it is lit. If there are enough LED strips to create a complete 360° spiral, then a single rotation of the shell sweeps the entire sphere. Thus for a complete shell you only need to spin at 25-60 Hz for a good persistence of vision effect.
I never built it but I would like to one day, I'm sure it would be fun, if not very expensive to make.
I notice current hardware still uses disks, so cylinders probably have disadvantages, too (possibly that they have to be either enormous or have a strongly curved surface, but I don’t see how the curved surface would be bad)
And yes, there’s current hardware (for the recording side). https://svi.nl/Spinning-Disk-Microscope:
“A Nipkow spinning disk microscope is one type of Fluorescence Microscope. A Nipkow disk is a spinning disk with a series of equally distanced circular holes of equal diameter drilled in it. It was invented by Paul Nipkow in 1885. Applied to a Fluorescence Microscope, it allows the sample to be scanned with an array of light points transmitted through these holes, participating in some of the advantages of a Confocal Microscope. Spinning disk microscopes are very good for living samples because they are fast and have relatively low phototoxicity. For fixed samples, a point-scanning Confocal Microscope is, in some cases, a better solution.
A Yokogawa Disk is a Nipkow disk with an array of microlenses in (or right after) the holes used in many commercial spinning disk microscopes.”
One manufacturer is https://www.suss-microoptics.com/en/products