Overhead Projector, Deluxe, ABS Body (Big), with Vari-Focal Technology

Quick Answer: The Overhead Projector, Deluxe, ABS Body (Big), with Vari-Focal Technology is the vari-focal version of the deluxe big-body projector in this range: a large ABS-bodied overhead projector whose head lens has a variable focal length, so the image can be made larger or smaller without moving the projector. A vari-focal overhead projector suits rooms where the projector has a fixed place but different screen sizes or seating arrangements are used.

Specifications

What Vari-Focal Means

A fixed-focal-length head lens produces an image whose size depends only on distance, so the whole projector has to be moved to fill the screen. A vari-focal lens contains lens groups that can be moved relative to each other, changing the focal length and therefore the size of the image from the same position. Unlike a true zoom lens, a vari-focal lens does not hold focus as the focal length changes, so the routine is to set the image size first and then refocus with the focusing knob.

This helps most in rooms with a fixed projector table or trolley position, such as tiered lecture rooms or halls where the projector must sit in an aisle, and where the same projector serves a small screen one day and a large one the next. The adjustment range of the lens is not stated in the listing and should be checked against the room. The rest of the projector follows the big deluxe ABS model, with its larger moulded body.

Transparencies for use with it are listed as OHP transparencies.

Looking After the Lens

• Operate the vari-focal ring or lever gently and within its end stops.
• Keep the head lens capped or covered when not in use; dust on a multi-element lens reduces contrast.
• Clean the outer lens surfaces only with a blower and lens tissue, and do not dismantle the lens.
• Allow the lamp to cool before moving the projector, and carry it by the base.

Applications

• Tiered lecture theatres where the projector position is fixed.
• Halls used with different screen sizes for lectures, meetings and events.
• Training rooms where seating changes and the image must be resized quickly.
• Physics lessons on lenses, using the projector itself to show how changing focal length changes image size.

Why Choose LabEquip

The vari-focal model is ordered by colleges and institutions whose lecture rooms fix the projector position but vary the screen size. LabEquip lists it in the General Lab Products range; to check lens range and suitability for your room, use the contact page.

Frequently Asked Questions

What is the difference between vari-focal and zoom lenses?

Both change focal length to alter image size. A true zoom lens keeps the image in focus while the size changes, whereas a vari-focal lens needs refocusing after each size adjustment.

Why use a vari-focal lens on an overhead projector?

It lets the image be enlarged or reduced without moving the projector, which is useful where the trolley or table position is fixed, as in tiered lecture rooms or aisles.

Do I still need to focus after changing the image size?

Yes. Set the image size with the vari-focal control first, then turn the focusing knob until writing is sharp across the screen.

Does changing the image size affect brightness?

Yes. A larger image spreads the same light over a bigger area, so it appears dimmer. Choose the smallest image that the back row can read comfortably.

Can this projector help teach lenses in physics?

It can. Students can see how moving lens elements changes image size, and the head shows how a lens and mirror form an image on a screen. Keep hands away from hot parts during demonstrations.

How does it differ from the big deluxe model without vari-focal?

Both share the larger ABS body and deluxe grade. The model without vari-focal has a fixed-focal-length head lens, so its image size is changed by moving the projector instead.

Last Updated: September 2026