2. OHP Acetate Presentations

OHP = Overhead Projector.

OHP equipment is fairly simple. A powerful bulb is enclosed in a box with a glass lid. Its light projects directly upwards where an overhead lens bends the beam 90 degrees so that you see a projection on a wall or screen.

To make a presentation, you place a transparent acetate sheet on the glass lid. Any text or drawings on the acetate sheet is then projected on to the wall or screen.

For many years this was the normal method of making a presentation and it still has some advantages compared to the laptop / projector method


Advantages Disadvantages
Limited equipment is needed - just an OHP and a screen. Easy to get the slides out of order, especially if there are a large number and there is not a lot of space around the OHP to store the acetates.
OHPs are fairly reliable pieces of equipment and don't break down very often. The only active part is the light bulb and a spare bulb is normally available in the projector should the main one fail during a presentation More difficult to print computer generated text / drawing onto acetate so tends to be hand-written / drawn
OHPs used to be cheaper than a laptop / projector combination, although this probably isn't the case nowadays Not very effective for full colour presentations
If the organisation has an OHP, only a handful of very light acetate slides has to be carried to the presentation venue compared to the weight of a laptop. No good for huge audiences such as a convention, as the projection screen is normally only suitable for a medium sized room
The presenter can scribble directly on to the acetate and make notes whilst they are interacting with the audience Not possible to have any dynamic effects e.g. transitions, animations
Excellent for free form drawing. You can place an empty acetate over an existing one then draw directly onto it without damaging the original Cannot produce hand outs from the technology although spare prints could be carried with the presentation
  Does not look as professional as a slick electronic presentation


challenge see if you can find out one extra fact on this topic that we haven't already told you

Click on this link: OHP Presentations