What is an Overhead Projector (OHP)

What is an Overhead Projector?

The overhead projector is probably one of the most versatile and useful visual aids that has been made available to the modern day lecturer. The overhead projector has long since replaced the traditional chalkboard as one of the main teaching aids and is used in lecture theaters and classrooms all over the world.

Even though computer-based data projectors are increasing in popularity, they are indeed very expensive and this means that they are in no way a match for the overhead projector. Therefore, it is very important for lecturers and teachers to know how to use overhead projectors effectively, so as to exploit its potential to the maximum level.

What are the Strengths of the Overhead Projector?

The overhead projector definitely has a number of advantages that would outdo most other visual teaching aids. For instance, a lecturer can use it in just the same way that he or she would use a chalkboard, but the biggest advantage would be that with the overhead projector, lecturers all over the world now get to face the whole class and maintain eye contact all times with their students instead of having to turn around and write. As a teacher, you would know that this eye contact plays a very big role in both facilitative as well as expository teaching, and serves both as a means of receiving feedback from the class on how good or bad the session is and as an outward non-verbal communication medium for the teacher.

Another very important benefit that the overhead projector has over the chalkboard is that it is multi-purpose and can be used to present pre-prepared material, which enables lecturers to build notes, tables, diagrams, and so on., and these can be used anytime, repeatedly.

If designed well and planned well, these overhead transparencies will provide all the aides and cues that are needed during a lecture, so that you don’t have to resort to the conventional note taking. These overhead transparencies are fairly compact when you compare them with some of the other types of visual aids like charts and can easily be stored in boxes, folders, files, or large envelopes.

As compared to most other projected visual aids, the overhead projector also has another big advantage, as it does not require a room to be darkened, so it allows students to take notes easily. It can also be used in any kind of room, except ones with extreme bright lights or in the direct sunlight.

The overhead projector is quiet, ‘user friendly’ and clean and requires no technical knowledge or skill on the part of the person operating it apart of course from the ability to change the lamps occasionally.

What are the Weaknesses of the Overhead Projector?

The drawbacks of the overhead projector include the basic fact that it requires a constant power supply and also requires a white flat surface on which its image can be projected. Another disadvantage is that if the surface is not suitable inclined at the correct angle, the image will suffer from a phenomenon called ‘keystoning’.

Unlike marker boards and chalkboards, overhead projectors require a small amount of maintenance. They are more likely to crack or break, so you must be very careful and always keep a spare bulb close at hand. Another disadvantage is that some teachers find the glare that is emitted from the overhead projector quite bothersome, even though this can be overcome by attaching a shade to the device.

Besides these hardware ‘glitches’, the basic problems that are associated with the overhead projectors arise from the fact that most users do not really provide enough thought or consideration to the production of their display material. The writing is generally too untidy or too small and cant be read easily, and apart from this it could also extend beyond the area of transparency. Lecturers and teachers always forget that this illuminated projection area in the overhead projector is not the same exact size as the acetate sheets that produce the transparencies. However, most overhead projectors are still of the older ‘square’ variety.

Lastly, lecturers and teachers tend to overuse these projectors only because they are so convenient. They employ it in situations where, on other occasions, other visual aids would have been more effective.

The advantages of using an OHP
Obviously the OHP, being economically and ecologically sound, can dramatically reduce the amount of paper used for photocopies: anything that can be photocopied can also be photocopied onto an OHT.

• Then again, if you want to give your students a record of the lesson, you can give them a photocopied paper version later.

• If you use an OHP you are effectively telling your students that your lesson has been well prepared and not something you thought of just before class.

• Your students can prepare visual stimuli themselves for presentations or class talks, or work together on separate strips of an OHT to put together an article or story, giving them a sense of achievement.

• You can photocopy a student’s work or a model composition onto an OHT and discuss its merits with your class. Similarly you can quickly present the answers to an exercise or a text which has been dictated for students to compare with their own, just as you can project the tape script after a listening exercise to point out anything of note such as new vocabulary to your students.

• The OHP also accommodates different learning styles and multiple intelligences as you can use colour for the text or drawings. Not only are colours and shapes attractive but they will appeal to and help your more visual learners and those who have a higher visual or spatial intelligence.

• There is lots of material that can be used for expressive speaking activities, such as photos, cartoons, maps, charts and diagrams, and of course you can make your own pro-forma game board of your favourite game or even TV quiz show.

• The OHP minimizes the time the teacher spends writing on the board, with his or her back to the class. You have, therefore, simultaneous control over your class and your materials. Materials can be prepared in advance but the teacher can also make additions. If you are bad at drawing it gives you the opportunity to prepare your picture: ‘Here’s one I made earlier’ solves your problem when your students can’t recognise what you are trying to draw. On the other hand pictures drawn spontaneously can of course be kept and used in later lessons. Again, students like this because it is something they have helped to create.

• You also have more control over the presentation of a text or an image since you can choose to modify it by masking or revealing parts of it. The OHP also allows the teacher to make a text or picture instantly available to the whole class. Finally, it offers variety and can be used to change the pace at any point in the lesson, aiding concentration and providing a useful role in discussions, role-plays and many other pair, group or whole class activities.