Projecting a Kaleidoscope: Lantern, Solar Microscope and Camera Obscura

3 days ago

7 min read

By Rocco (Roi) Ramon - licensed architect, founder of Studio Yabaye

A kaleidoscope is built for one eye. The pattern exists only for a viewer placed at the narrow end of the mirrors. Two years after his 1817 patent, Sir David Brewster described how to remove that limit and throw the pattern on a wall.

I work here from Brewster's "A Treatise on the Kaleidoscope" (Edinburgh, 1819), referred to below as the Treatise. The projection chapter is Chapter XIII in that edition and Chapter XV in his enlarged 1858 book. This article reports what the chapter says, then lists later instruments in museum collections.

Three projection devices of Brewster's day

Chapter XIII adapts the kaleidoscope to three existing instruments:

The projection lantern. A lamp, a condensing lens, a transparent painted slide and a projecting lens, used to throw an enlarged picture on a wall in a dark room. Brewster refers to its "sliders", which slide through a groove.
The solar microscope. A projection microscope mounted in an opening in a window shutter. Sunlight replaces the lamp, and the enlarged image of a small object is thrown into the darkened room.
The camera obscura. A dark room or box in which a lens forms an image of the outside scene on a white surface or a ground glass.

Brewster's proposal is to place the mirrors between the object and the projecting lens.

Brewster's arrangement: lamp, object cell, mirrors, lens, wall

The chapter opens with the limit it sets out to remove. In every form described up to that point, the pictures are "visible only to one person at a time". Brewster states that it is not difficult to exhibit them on a wall "to any number of spectators".

The apparatus, in the order the light passes through it:

Light source. A lamp or candle. Behind it sits a mirror that returns part of the light.

Condensing lens. A lens concentrates the direct and the reflected light on the objects.

Object cell. The objects sit in a cell at the far end of the mirrors, as in a hand-held kaleidoscope. The cell either rotates about the axis of the tube or slides through a groove like a lantern slide.

Reflectors. The tube with its mirrors.

Projecting lens. A lens is placed at the eye end, close to the ends of the reflectors, with its centre on the centre of the eye aperture. It takes the place of the eye.

Screen. A wall covered with white paper or another white ground, so that the colours show.

The focal length rule

Brewster gives a design rule for the projecting lens. Its focal length must be less than the length of the reflectors.

He then narrows the range. At half the length of the reflectors, the image forms at a distance equal to the length of the reflectors and is no larger than the circular field seen in the instrument. That is too small. His recommendation is a focal length of two-thirds or three-fourths of the reflector length. Longer than that, the image forms too far from the instrument.

Sunlight, oxygen lamp and a lecture hall

Solar microscope. In daylight the objects are lit by the rays of the sun, and the mirror behind the lamp is not needed. The kaleidoscope is attached to the part of the solar microscope frame that enters the opening in the window shutter.

Safety note. This is a historical description, not an instruction. Sunlight concentrated by a lens can start a fire and can cause permanent eye damage. Do not aim a lens or a kaleidoscope at the sun.

Oxygen lamp. Brewster names the brightest source available to him: a lamp burning in oxygen. He reports that one of Mr Bate's polycentral kaleidoscopes was fitted with such a lamp for the lectures on natural philosophy given at Guy's Hospital by the chemist William Allen.

Projecting real scenes: the camera obscura version

The second half of the chapter applies the same idea to the compound kaleidoscope, the form that takes its pattern from outside objects through a lens. The present-day relative of that form is described in what is a teleidoscope.

Two rooms. The object plate is removed. A lens is placed at the object end and adjusted until the image of the outside objects falls exactly on the ends of the reflectors. Brewster lists flowers, statues, human figures and large pictures as subjects, strongly lit in one room, at six inches to twelve feet from the lens. The pattern is shown on the wall of the next room.

Outdoor subjects. For trees and shrubs, the kaleidoscope with its two lenses is fixed in the circular opening of a window shutter. The picture is received on white paper, as in a camera obscura.

Portable camera obscura. The assembly can also be placed in the movable drawer of a portable camera obscura. If the lens forms its image inside the box, the pattern appears on the ground glass and can be copied.

The problems Brewster identifies

Small aperture. The opening at the eye end has to be small, and all the light for the wall passes through it. He writes that this is hostile to exhibition, because it "requires a very intense light".

A larger aperture does not help. Opening the aperture to gain light has two penalties. The light of the reflected images is diminished, and "the picture loses its symmetry at the centre".

Longer mirrors, with a drawback. His only remedy is to lengthen the reflectors and widen them in proportion. If mirrors five inches long allow an aperture of a quarter of an inch, mirrors ten inches long allow half an inch with the same symmetry. Longer mirrors then need a projecting lens of longer focal length, so the image must be received far from the instrument.

Mirror angle and objects. For brightness he names inclinations of 30, 36 and 45 degrees. Objects should be as thin as possible, and none with dark tints should be used.

Chapter V of the Treatise treats the intensity of light in different parts of the field. It reports that at an inclination of about 30 degrees, with the eye near the angular point, the light is close to uniform across the sectors, and that at 18 or 22 degrees the difference between sectors is obvious.

After Brewster: projection instruments in museum collections

Projection kaleidoscopes. Instrument makers did build the device. The Science Museum Group holds "Darker's Projection kaleidoscope", dated about 1877 and made in Lambeth: two mirrors in a V arrangement at 60 degrees in a brass tube, between two lens elements with adjustable separation, giving a six-fold image. It was fitted to a lantern by a screw flange. The same collection holds two kaleidoscope lantern slides with mahogany sliders, one marked Newton & Co., 3 Fleet Street, London, dated 1820-1870.

The chromatrope is a different mechanism. Lantern shows also used the chromatrope slide. It has no mirrors. Two painted glass discs turn in opposite directions, driven by a handle with rackwork or by a double string and pulley. The symmetry is painted on the discs, not produced by reflection.

Checklist: reading a kaleidoscope projection

Light source strong enough for the image size.
Room dark, screen white.
Sectors compared for brightness, first to last.
Centre of the pattern checked for loss of symmetry.
Joints between sectors checked at full enlargement.
Mirrors present, or painted discs.

FAQ

Can a kaleidoscope be used as a projector?

Yes, with added optics. Brewster's 1819 Treatise, Chapter XIII, places a strongly lit object cell at one end of the mirrors and a lens at the eye end, which throws an enlarged image on a white wall. An ordinary hand-held kaleidoscope has no projecting lens and no light source of its own.

Who first described projecting kaleidoscope patterns?

Sir David Brewster described it in Chapter XIII of "A Treatise on the Kaleidoscope", published in Edinburgh in 1819. He reports that one of Bate's polycentral kaleidoscopes was fitted with an oxygen lamp and shown at William Allen's lectures on natural philosophy at Guy's Hospital.

What lens did Brewster specify for projection?

A lens at the eye end, close to the reflectors, with a focal length shorter than the reflectors and longer than half their length. He recommends two-thirds or three-fourths of the reflector length. At half the length the image is too small, and above three-fourths it forms too far away.

Why is a projected kaleidoscope image dim?

All the light must pass the small aperture at the eye end of the mirrors. Brewster writes in 1819 that this requires a very intense light. Enlarging the aperture weakens the reflected images and breaks the symmetry at the centre, so his remedy is longer and proportionally wider mirrors.

Is a chromatrope a kaleidoscope?

No. A chromatrope is a lantern slide with two painted glass discs that rotate in opposite directions, driven by a handle with rackwork or a double string and pulley. It contains no mirrors. The radial pattern is painted on the glass, while a kaleidoscope produces its symmetry by reflection between inclined mirrors.

What is the difference between projecting and looking through a kaleidoscope?

In the instrument, one eye sits near the angular point of the mirrors, where the sectors join, and the viewer turns the object cell. In a projection, a lens replaces the eye, the image is spread over a screen for many viewers, and it needs far stronger light and a dark room.

About Studio Yabaye

Studio Yabaye builds kaleidoscopes and teleidoscopes with front-surface mirror systems in several configurations, in a brass tube, cut, fitted and hand-finished in the studio. The instruments are built for one viewer at the eyepiece. The studio is based in Israel and ships worldwide. The current range is at all products, and questions can be sent through the contact page.