Notes on use
The use of the OHP or data projector sends a message:
“This has been prepared.” This is in contrast to using the whiteboard or
flip-chart, which sends “This is spontaneous,” or, "I am reacting to you". There is a case for both kinds of
message, of course, under different circumstances.
Data projectors are becoming increasingly
popular and more frequently built in to classrooms. If you have to choose, consider
|Not much to go wrong: and if it does, you can
often fix it yourself
||Requires a computer as well, and a link: there's
a lot of temperamental hardware.
|Restricted in the range of media it can use:
OHTs and a few transparent or silhouetted objects
||Can use static or animated graphics, sound and
even movie clips, with a sufficiently powerful machine
|Can easily take OHTs out of sequence, to re-cap
or jump ahead to respond to a question.
||Needs a dual-monitor set up, if students are not
to see the nuts and bolts of the set-up when you want to select a slide out of order (learn to blank the screen while you do it)
|OHTs are bulky and rather fragile
||You can put an entire lecture sequence's
material on one floppy—your entire teaching career's output on CD or DVD.
|Temptation to use badly-designed OHTs: pages of
books copied onto transparencies, for example.
||Your presentation package makes it harder to
produce a bad show than a good one.
|You can write on and otherwise amend OHTs on the
the whole you are stuck with what you have prepared.
|Students can use write-on OHTs for reporting
back from groups, etc.
||Not really practicable, except with a smart-board
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
- 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.
- Are they parallel? Do the two channels carry
the same information, with the one reinforcing the other? That may be useful on occasion,
but if you are reduced to reading out verbatim the contents of the OHT (except when it is
for the benefit of students with difficulties), the redundancy level may be too high. That is the root of "death by PowerPoint".
- Are they complementary? Do the two channels
carry different information? This is often the case when the OHT is used for graphics.
More visually-oriented students may find it difficult to pay attention to what is being
said when concentrating on the screen: more aurally-oriented students may find their
natural tendency to listen to the voice hinders their ability to make sense of the image.
Give the students a few moments to digest what they are seeing before commenting on it.
You are requiring the students to look:
when they are looking at the screen, most of them will not be able to make notes, so a
lecture or class which uses a lot of OHTs may also require handouts, if it is the kind of
session which calls for notes. Remember, too, that copying diagrams or charts from a
screen takes much longer than making text notes. Keep graphics simple. Be explicit about
what is worth noting and what not. However, if leaving time for copying breaks up the
session too much, think again about providing the information in other ways, too. If your
material was prepared in one of the standard presentation packages, it could be exported
directly to an intranet or Virtual Learning Environment (VLE), for example, for consultation after the session.
(Presentation packages may
provide an automatic "Export
as Web Page" facility).
Tips for use
It's sucking eggs time again! Get the OHP
set up for optimum image size, focused, etc. before the class starts. Make sure
everyone can see.
- Once you are sure of the above, you have
no need to look at the screen. You can concentrate on the class. Needless
(?) to say, don't get in their way.
- So do not point to material on the
screen itself. Use a pen or other pointer on the stage of the OHP. If your hand is at
all shaky, lay the pointer down on the OHP stage. Standing in front of the screen to point
out salient topics:
- means that you are tempted to talk to the screen and not the
- means that some of the image is projected onto you, and there
is a large obscuring shadow on the screen
- The only exception is when you are projecting
onto a whiteboard, and writing/drawing on the board to elaborate on the image. (This is
also the only occasion when you should project onto a whiteboard, which will also reflect
back the light source, and may well form a "hot-spot" obscuring the image for
some students.) Even this can usually be dealt with more effectively by writing on an
overlaid transparency on the OHP stage.
- Do not leave an old OHT showing when you have
moved on to talk
else. Switch off between OHTs, or at
least between sequences.
When I started using the OHP years ago, this was not advocated,
because it shortened the life of the bulbs, and a blank screen was a small price to pay to
avoid the risk of a bulb blowing and the disruption that caused. Modern halogen lamps are
less sensitive (although it is still not advisable to move an OHP until it has thoroughly