Slide Projector Product

Overview

A slide projector is a simple optical relay run by a clever mechanism. Light from the Lamp House passes through the Condenser Optics, through a mounted 35mm transparency sitting in the film gate, and out through the Projection Lens to the screen. The Tray Transport swaps slides in about one second per cycle, and the Cooling System system carries off the several hundred watts of heat that would otherwise destroy both lamp and slides.

The design described here is the rotary-tray (carousel) layout: slides ride in a removable Rotary Slide Tray of 80 compartments on top of the machine and drop into the gate by gravity. The geometry is self-protecting — a jammed or badly mounted slide simply fails to drop, rather than being forced into the gate.

Illumination path

The Halogen Lamp is a 24 V 250 W tungsten-halogen capsule whose compact filament sits at the focus of the Dichroic Reflector. The reflector is a cold mirror: its multilayer coating reflects visible wavelengths forward but transmits much of the infrared straight through the glass and out the back of the lamp house, removing a large fraction of the heat before it ever heads toward the slide.

The Condenser Optics implements Köhler-style illumination. The aspheric Rear Condenser Lens collects a wide cone from the lamp; the Front Condenser Lens images the filament into the aperture of the projection lens rather than onto the slide. Because the filament is imaged into the lens pupil, its structure never appears on screen and the slide is lit evenly corner to corner. Between the two elements sits the Heat-Absorbing Glass, a tempered heat-absorbing filter that soaks up the residual infrared — without it, a cardboard-mounted slide warps within seconds in the gate.

Slide transport

One press of the forward button runs a complete change cycle from the Lifter Cam, a single-revolution cam turned by a small Servo Motor through reduction Helical Gear Pair gearing. The sequence: the Slide Lifter Arm raises the current slide out of the gate and back into its tray slot; the tray indexes one position, registered by the Tray Detent Pawl so the next compartment lands exactly over the drop slot; the lifter lowers and the new slide falls into the gate under gravity. Reverse runs the same cycle with the index direction inverted. The tray's locking ring keeps all 80 slides captive when it is lifted off the spindle, so a loaded tray can be stored like a book.

Projection lens and autofocus

The Projection Lens slides into the front bore on a toothed Lens Barrel Rack. An 85 mm f/2.8 lens fills a 1.8 m screen from about 4 m; interchangeable barrels from 35 mm to 250 mm cover everything from tabletop rear projection to lecture halls. Focus is motorised: the Autofocus Sensor bounces an infrared beam off the slide surface onto a split photocell. When a slide heats up in the gate and "pops" — the film bowing a millimetre out of plane — the reflected spot shifts, and the control board drives the focus Servo Motor to follow it. The same motor responds to the focus rocker on the Wired Remote.

Cooling and control

The Blower Motor pulls room air through the Intake Filter and the Air Duct splits it between the lamp envelope, the heat glass, and the gate. The lamp is interlocked to airflow, and two Thermal Fuse elements — one in the lamp house, one behind the duct — open the lamp circuit if either airflow fails or the Heat Shield region overheats. After switch-off the blower keeps running until the lamp house cools, which is the main determinant of lamp life: halogen capsules fail early when cooled too fast or handled with bare fingers.

Sequencing lives on the Control Board: an Microcontroller reads the remote contacts through the DIN Connector, fires the lamp Relay, and drives the lifter and focus motors through Power MOSFET stages. The Power Supply is dominated by the lamp transformer stepping mains down to 24 V at over 10 A, with a small auxiliary winding for the logic. The Remote Button Set in the handset are plain contact closures on a 4 m Remote Cable — there is nothing in the remote to go wrong, which is one reason projectors of this pattern from the 1970s still run.

Setup

The machine sits on its Elevation Foot, a screw jack that tilts the optical axis up at the screen; keystone distortion from extreme tilt is the practical limit. The Carry Handle folds flush beside the tray well, and the housing shells (Sheet Metal Panel) lift off for lamp changes via the quick-release Lamp Socket carrier.