OHP/Overhead Projector – Transparencies/Slide

Quick Answer: The OHP/Overhead Projector – Transparencies/Slide listing covers transparent film sheets placed on an overhead projector, so that text and diagrams on them are projected onto a wall or screen. OHP transparencies let a teacher write, draw and build up a diagram while facing the class.

Teaching with Overhead Transparencies

An overhead projector shines light up through a transparent sheet lying on its glass stage and throws an enlarged image onto a screen behind the teacher. Anything on the sheet appears on the wall, so the teacher can keep eye contact with the class while writing an equation, labelling a diagram of the heart, or adding arrows to a food web. Sheets can be kept and reused, which is why many teachers build a file of transparencies for each topic.

The listing does not say whether the sheets are blank film for writing and printing or pre-printed teaching transparencies, and film for printing must suit the machine. Laser printers and photocopiers need heat-resistant film, while inkjet film has a coated surface that holds the ink; plain writing film is used with OHP pens. State the type and sheet size you need when you enquire.

Overlays are a particular strength. A base sheet showing a leaf outline can be covered in turn with sheets adding the vascular tissue, the stomata and the labels, and the same approach works for maps, circuit diagrams and graph plotting. The sheets are grouped with projection items in the Microscope & Optics range.

Applications

• Building up labelled diagrams step by step in front of a class
• Overlay sequences, such as a leaf outline with tissue layers added in turn
• Projecting a graph grid for plotting class results from a practical
• Showing a worksheet or answer key to the whole room

Specifications

Care & Handling

• Handle OHP transparencies by the edges and store them in clear sleeves or between sheets of paper, so they do not scratch or stick together.
• Use water-soluble pens for anything you want to wipe and reuse, and permanent pens for master sheets.
• Feed only film made for your printer or copier; the wrong film can melt inside a laser printer.
• Keep sheets away from the projector’s warm lamp housing when they are not being shown.

Why Choose LabEquip

Schools and training centres that still teach with overhead projectors buy transparencies for each term. Send the film type, sheet size and quantity through the contact page; for photographic biology images, the 35mm projection slides are a related LabEquip item.

Frequently Asked Questions

What is the difference between laser and inkjet transparency film?

Laser film is made to survive the heat of a laser printer or copier fuser. Inkjet film has a coated side that absorbs ink so it dries without smudging. Inkjet film fed through a laser printer can melt and damage the printer.

Which OHP pens should I use?

Water-soluble pens wipe off with a damp cloth, so the sheet can be reused. Permanent pens resist smudging and suit master diagrams that will be shown many times, and they can still be removed with alcohol if needed.

Why does my projected image look blurred at the edges?

Adjust the focus knob on the projector head and check that the head faces the screen squarely. A tilted screen or projector causes keystone distortion, where the image is wider at the top than at the bottom.

How do I stop sheets curling on the projector?

Put a clear glass or plastic weight along one edge, or mount the sheet in a card frame. Storing sheets flat rather than rolled also prevents curling.

Can I print coloured diagrams on transparencies?

Yes, on film that suits a colour printer. Colours look paler when projected, so choose strong colours and thick lines, and test a single sheet before printing a full set.

How do I clean a transparency?

Wipe water-soluble ink off with a damp, lint-free cloth. For fingerprints, use a soft cloth moistened with water and a drop of mild detergent, then dry it. Avoid solvents on printed sheets, as they can lift the ink or toner.

Last Updated: September 2026