Quick Answer: The Overhead Projector, Regular, Sheet Metal is a transmissive overhead projector (OHP) with a housing of formed sheet metal: a lamp in the base shines up through a glass stage and a transparency, and a head above turns the image onto a screen. A sheet metal overhead projector of this regular grade is the conventional classroom pattern for teachers who write or draw on transparencies while facing the class.
From Lamp to Screen: The Optical Path
Inside the base, a lamp with a reflector sends light upward through a large, flat Fresnel lens set just beneath the glass stage. The Fresnel lens, a disc of fine concentric ridges, acts as a condenser, bending the light so that it converges on the projection head. Anything placed on the stage, whether a written transparency or a transparent object, interrupts that light. In the head, a lens focuses the image and a mirror turns it through roughly a right angle towards the screen behind the teacher. Raising or lowering the head on its arm brings the picture into focus.
The regular sheet metal version is the conventional form of this design: the body is formed from metal sheet, usually painted or powder coated, which gives a rigid base that resists knocks and conducts heat away from the lamp housing. Metal bodies can dent if dropped and should be kept dry to protect the finish. How the regular grade differs from the economy and deluxe models in this range, and the lamp type, are not specified in the listing.
Blank or printed OHP transparencies are needed for writing, and the picture is shown on a wall-hung screen such as the manual projection screen.
Specifications
| Type | Transmissive overhead projector (OHP) |
| Body | Sheet metal housing |
| Grade | Regular |
| Optics | Fresnel condenser under the stage; lens and mirror in the head |
| Focusing | Head moved up or down on its arm |
| Lamp type, stage size and power rating | Confirm at enquiry |
Classroom and Laboratory Uses
- Writing notes, equations and worked examples on transparency film while facing the class.
- Showing magnetic field patterns: iron filings sprinkled on a transparent sheet over a bar magnet on the stage.
- Projecting transparent rulers and protractors for whole-class measurement practice.
- Presenting printed diagrams and exam questions from prepared transparencies.
Care of the Projector
- Let the cooling fan run until the lamp has cooled before moving the projector; jolting a hot lamp shortens its life.
- Clean the stage glass with a soft cloth and glass cleaner; wipe the head lens and mirror only with a lens cloth.
- Do not place liquids directly on the stage glass; use a transparent tray or dish.
- Carry the projector by its base, not the head arm, and store it covered to keep dust off the Fresnel lens.
Why Choose LabEquip
Sheet metal overhead projectors are still ordered by schools, coaching centres and training institutes where transparency teaching is routine and a sturdy housing is wanted. LabEquip lists this model in its General Lab Products range; ask about lamp type and spares on the contact page.
Frequently Asked Questions
How does an overhead projector work?
A lamp in the base shines light upward through a Fresnel lens and the transparency on the glass stage. A lens in the head focuses the image, and a mirror turns it towards the screen behind the presenter.
What is the Fresnel lens under the stage for?
It is a flat lens made of fine concentric ridges that acts as a condenser. It bends the light from the lamp so that it passes through the whole transparency and converges on the projection head, giving an evenly lit image.
Why choose a sheet metal body over ABS?
A sheet metal housing is rigid, resists cracking from knocks and conducts heat away from the lamp. ABS bodies are lighter and cannot rust, but can crack if dropped. The choice depends on how often the projector is moved and the room conditions.
How do I focus the image?
Turn the focusing knob to move the head up or down the arm until the edges of the writing are sharp. If the image is too large or small, move the whole projector nearer to or further from the screen first, then refocus.
Can I show experiments on the stage?
Yes, transparent experiments work well. Iron filings over a magnet show field lines, and shallow dishes of coloured solutions show reactions. Keep liquids in a tray or dish, never loose on the glass, and keep hot objects off the stage.
Why are the corners of the image dark or coloured?
Dark corners or coloured fringes usually mean the head is not square to the stage, the Fresnel lens or mirror is dirty, or the lamp is ageing. Check that the head sits squarely, clean the optics and replace a blackened lamp.
Last Updated: September 2026
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