OVERHEAD PROJECTOR PRICE IN PAKISTAN IN KARACHI

overhead projector

2000 lumens
2 lamp
new projector

The essence of the OHP and the Data Projector

In order to put the following tips into context, consider a few points about the OHP in the classroom:

The OHP is usually under the control of the teacher: this means that it is by default an instrument of teacher-centred instruction. This is not necessarily a bad thing, and teachers can develop its use as a tool of session management. Switching it on, for example, is likely to send the message, "Now get ready for some input from me", and can be used to curtail discussions which are veering off the point. Similarly, switching it off when a discussion starts is a way of acknowledging that the class group is making the running.
One teacher I observed recently worked mainly on a flip-chart: she just used the data projector to project single key words about the topic the class was working on. It was very effective in helping the students to keep track.

It presents a series of images in sequence: the timing and ordering is again controlled by the teacher. Indeed, having a series of OHTs can readily substitute for the teacher having to have her own notes, and free her up to pay more attention to the class, and to expound the material more spontaneously.
But the fact that each image is shown for a limited period of time means that its content needs to be digestible within that period. So apart from sheer legibility issues, there should not be too much on any one OHT.
It is, of course, a visual medium: this requires attention to the needs of students who may not find it accessible. These include not only students with visual impairments, but also dyslexic students. There is some evidence to suggest that the high contrast of the screen, which is a help to many students, can hinder the reading of those who have some forms of dyslexia. Students with hearing impairment may find it difficult to follow the lips of a lecturer and look at the screen at the same time.
Conventional text is linear: we all know it takes time to read. Graphics, including some non-conventional text such as mind-maps, and labelled diagrams, are perceived at once as a whole, and then "read" in unpredictable orders by different students. This comes more naturally to some students than others. You have two channels of communication going at the same time, assuming that you are talking at the same time. You need to consider how they interact.