4. DEFINITION
Overhead projector is a device for projecting
a matter, which is written or drawn on
transparent sheet of acetate on to a screen.
6. It projects tranperancies with brilliant
screen images suited for use in lighted
room
The teacher can draw diagrams on the
transperancy while he teaches, these are
projected simultaneously on the screen of
the over head projector
7. Purposes of Overhead Projector
To develop concepts and sequences in a subject matter area.
each component part can be presented as the teacher senses
the students’ readiness for the next step use
To test students’ performances, while others classmates
observe.
To show relationships by means of transparent overlays in
contrasting color.
8. Purposes of Overhead Projector
To make marginal notes on the transparencies for the use of
the teacher that can be carried without exposing them to the
class, when projected.
As a recording device for presenting minutes of a group
discussion visually.
To give illusion of motion in the transparency
To show statistics and other graphs of mortality and
morbidity rates of various diseases.
9. USING AN OHP
Place the OHP on a stable table with the objective lens facing the screen behind the
teacher
Put the cord plug into a power wall-socket. Switch on the blower first and then the
bulb
Place the acetate or cellophane transparency on the glass top
Move the objective lens and mirror assembly up and down to get the image in focus
on the screen
Explain about the material on the transparency sitting behind the overhead
projector with a small pointer.
11. OHP Transperancies
Transparencies are simple to easy to prepare.
10x10 inch sheet with printed written or drawn material is
placed on the platform of the projector and a large image is
projected on screen.
The projector is used from rear to the front of the room with
the teacher standing beside the projector.
13. Articles Required for preparing Transparency
Acetate sheet
single/roll
Washed X-ray plate.
Best are acetate –
Cellophane paper
pens:
• Spirit based inks permanent use
• Water based ink (temporary use)
• Spirit based can be erased with methylated spirit and water based with clamp cloth
• Lined paper or grid sheet.
A Paper/frame and
Masking Tape
14. Have one main
idea for each
transparency
Include only
related figures
and diagrams
Ensure that all
transparencies
are as simple as
possible & easy to
read
Avoid too much
information on any
single
transparency
Use a simple letter
style
Do not use all
capital letters
Do not overcrowd
it.
Use diagram in
proportionate to its
lettering
Use colour and
words with
discretion
Guidelines for making effective transparencies
15. Preparation of OHP Transparencies
Use a standard size of acetate sheet measuring 18 cm -22.5 cm.
OHP markers are available in two types; temporary and permanent.
Temporary markers have soluble ink and written matter can be wiped off with the help of a damp cloth.
Permanent markers are oil, spirit or wax based and their writing is preserved for long time. One may prepare
reusable transparencies with permanent OHP markers. Additions and alteration during teaching should be made
with water soluble OHP markers so that the same are wiped off after use. If you want to reuse the transparency
sheet later for another purpose, be sure to use a marker with soluble ink.
Transparencies must be clearly written with at least 8 mm size letters either free hand or by transfer letters or
template, etc. A transparency which can be clearly read from a distance of 2 m should project well for a
classroom 6 m deep. Transparencies should be patiently prepared with bright harmonizing or contrasting colors,
legibly and systematically. There should be no more than six words in each line and no more than eight lines in
each transparency. Put margins appropriately. Of the various types of visuals, diagrams, schematics, cue words,
cartoons and graphs make better visual for the OHP.
16. Preparation of OHP Transparencies
The best colors to use to write on transparencies are black, blue and green. Use red sparingly. It is not a color that
project well.
Whether you are drawing the image on the transparency or copying it from a printed page, keep the amount of
information on the sheet to a minimum and make the image large enough so that students in the back of the room
will be able to see it.
Avoid copying information from a printed book or journal page or a type written sheet. Such pages present too
much information for the students to take in and the print is usually too small for them to see easily. If you want
to type some information on to a transparency, type it on paper first, enlarge the type on a copier with an
enlarging function and then make a transparency by taking photocopy of The material.
Transparencies can be very creative, especially if you have artistic help. If you have produced a transparency
worth saving for future classes you may want to mount it in a cardboard frame that gives it some protection,
enables you to handle it without touching the acetates and reduces glare around the image.
17. Method of Preparing
Placed lined paper or 6 mm lined grid sheet beneath acetate sheet before
writing the material
Use simple lettering style 6 mm for text and 9 mm for titles. Use capital letters
for titles. Limit the written material to six lines in each transparency. Use only
one lettering style and space it for regular and even look.
Use thick chart paper or readymade frame for framing the transparencies for
better and neat looks. Use masking tape rather than cellulose tape to prevent
from brittleness from heat.
Store from flat, clean and interlocked with paper.
18. Masking and Overlay Techniques
Spot masks
Sliding
masks
Pleated or
folding
masks
Circular
masks
Overlays
19. Specific Techniques Used in OHP
Progressive
Disclosure
Silhouetting Overlays
Using
Detached
Movable
Parts
20. Points to remember during OHP Presentation
Keep the screen above participants head
Keep the screen in full view of participants
Darken the room
Turn off the screen if you are going to talk for more than two minutes
Switch off the bulb of OHP to save electricity but fan must be running to keep it cool
Do not move the OHP during use
21. Advantages of Overhead Projector
Projects large amount of
materials including pictures &
diagrams
Cheap and can be reused
Attractive, easy to prepare,
requires limited planning and
time saving
Progressive disclosure of
content increases attention
span
Permits face to face
interaction
Easily available & Easy to
operate & handle
22. Disadvantages of Overhead Projector
Cannot be used
in situations of
power supply
interruptions.
Its not possible to
use outside the
classroom
Its difficult to
transport
Good handwriting
is essential to
prepare good
transparencies
