by An overhead projector (OHP), like a film or slide projector, uses light to project an enlarged image on a screen, allowing the view of a small document or picture to be shared with a large audience.
You may consider overhead projectors to be yesterday’s technology, but when you know you’ll be making a presentation in a facility that relies on them, you can set up an effective set of projection materials that work just as well as digitally projected output. Instead of carrying your presentation on a thumb drive or CD, plan on toting along a box of transparencies, as well as a few extras tools to add depth to your talk.
In the overhead projector, the source of the image is a page-sized sheet of transparent plastic film (also known as ‘foils’) with the image to be projected either printed or hand-written/drawn. These are placed on the glass platen of the projector, which has a light source below it and a projecting mirror and lens assembly above it (hence, ‘overhead’). They were widely used in education and business before the advent of video projectors.
Use in education
Overhead projectors were widely used in education and business before the advent of computer-based projection.
The overhead projector facilitates an easy low-cost interactive environment for educators. Teaching materials can be pre-printed on plastic sheets, upon which the educator can directly write using a non-permanent, washable color marking pen. This saves time, since the transparency can be pre-printed and used repetitively, rather than having materials written manually before each class.
The overhead is typically placed at a comfortable writing height for the educator and allows the educator to face the class, facilitating better communication between the students and teacher. The enlarging features of the projector allow the educator to write in a comfortable small script in a natural writing position rather than writing in an overly large script on a blackboard and having to constantly hold their arm out in midair to write on the blackboard.
When the transparency sheet is full of written or drawn material, it can simply be replaced with a new, fresh sheet with more pre-printed material, again saving class time vs a blackboard that would need to be erased and teaching materials rewritten by the educator. Following the class period, the transparencies are easily restored to their original unused state by washing off with soap and water.
Page Size
When you design a presentation for an overhead projector, you’ll want to set up your working document to match the size of the medium on which you’ll print it out. Regardless of whether you’re targeting a networked colour copier, laser or inkjet printer, the transparency film you buy comes in one size: 8.5 inches by 11 inches. Although you won’t want to crowd each sheet of film with more content than you can project legibly, you also don’t want to work on a document that doesn’t match your output dimensions.
Page Coverage
Especially if you plan to attach your transparencies to cardboard frames for easier handling, leave generous margins around your content to enhance its effectiveness when you project it. Just as you’d set up PowerPoint slides following the 7×7 rule no more than seven lines of type, each with no more than seven words add type sparingly to each page you prepare for overhead projection. Avoid simply summarizing your talk in a series of unedited bullet-point pages that add nothing to your message.
Blanks and Writing Tools
Because overhead transparencies accept hand-written annotations in grease pencil, you can plan ahead for those portions of your talk in which you ask your audience for comments. Adding blank sheets of film to your stack of printouts enables you to ask questions and record the replies. If you bring extra blanks with you, you can accommodate long sets of suggestions without resorting to too-small handwriting to write down all the input. Bring spare grease pencils so you don’t have to stop if your point wears down, as well as a paper towel to use as an eraser.
Paper Copies
To give yourself a convenient reference to what you’re projecting, print your entire set of overheads once on transparency film and again on plain bond paper. If you store your overheads in a box, you can interleave the paper copies with the transparencies. When you want to check what you’re about to project, or refer back to a previous transparency, you can look at your paper printouts instead of fumbling through a stack of plastic sheets in a darkened room. The paper copies also help protect your transparencies from static cling.
Advantages
Whether you prepare support materials for in-house or client presentations in Microsoft PowerPoint or pull together the equivalent of PowerPoint slides from a variety of applications, you want a projector solution that fits your budget and accommodates your needs. Overhead projectors may lack the high-tech appeal of LCD-based digital projectors, but they offer advantages that may make their time-tested design a good fit for your office.
Simple Technology
An overhead projector relies on a bright lamp that sends an image through a lens-and-mirror assembly onto a screen. With the exception of the fan that cools the lamp, these devices contain no moving parts. If you want to project movies and sound, an overhead projector won’t meet your needs, but it also doesn’t require cables and software troubleshooting, or force you to reboot a misbehaving computer to complete a presentation. Compared to computer-connected LCD projectors, overhead projectors provide uncomplicated service based on reliable low-tech components, and don’t require you to learn new technologies or skills.
Equipment Costs
Overhead projectors carry a price tag that can run from 10 percent to 50 percent of the cost of their LCD-based cousins. Both device types use specialized lamps, but the price differential continues when you evaluate their parts head-to-head. In some cases, you can buy a new overhead projector for the cost of an LCD projector lamp. If you present materials that don’t require computer projection of A/V content, an overhead projector will save you money, both when you buy it and over its functional life.
Transparencies
Transparency film may cost more than regular office paper, but it’s available at virtually any office-supply store, local or on the Web. If you prefer to purchase environmentally friendly materials, look for transparencies with recycled content. Regardless of whether you use a laser or inkjet printer, or direct your output to a networked colour copier, you’ll find a film product formulated for your device. You can prepare your transparencies well in advance of your presentation and reuse them each time you give the same talk. If parts of your message change, replace the outdated transparencies with new ones.
Annotations
Because overhead projectors display anything you print onto sheets of clear plastic material, their transparencies make it easy to annotate your presentation pages with comments you elicit from your audience or points of emphasis related to your data. With an inexpensive wax or grease pencil, you can write or draw on your transparencies during your talk and wipe the notes away with a tissue or paper towel. Overhead projectors can’t display anything through opaque materials, so you can cover parts of a transparency with a piece of cardboard and reveal your talking points one at a time, focusing audience attention.
Advantages of overhead transparencies
- Transparencies are easy to make. Simply prepare your visual aid on paper and then copy it on a copier. But instead of copying onto blank paper, copy onto a transparency. This way you can make transparencies quickly, revise them quickly, and revise them often. You can also make them yourself, without waiting for a professional staff to produce them for you. This convenience often translates into whether people update their presentations or let them go stale.
- They’re cheap. They cost only pennies a copy.
- They ‘re portable. For most presentations, you can easily fit your transparencies in your briefcase with room to spare. This is no small matter if you travel often. If you use cardboard frames around your transparencies, you increase the bulk somewhat, but they’re still quite portable.
- They let you be flexible. You can rearrange your presentation on the fly with the audience staring at you to meet new needs. For example, occasionally someone needs an answer now for something you planned to cover later. No problem: just reach for the appropriate transparency and press ahead.
- You can write on them. Sometimes you don’t want the audience to see a static visual aid (like a ready-made equation); instead, you want to create it, step by step, as the audience watches. With a transparency, you can do that easily. Some pens are designed for that purpose. An added advantage is that you can easily erase your writing later with a damp paper towel (if you’re like me, however, you may walk around for a day or so with red or green or blue fingers).
- You can see what’s next. Since most speakers handle their own transparencies, they can glance at the label on the next one and see what the next topic is. That’s a really important advantage; otherwise, part of your mind is constantly trying to remember what’s next. Sneak glances are no problem with overheads.
- They can look extremely professional. Color printers and copiers can enhance your message by drawing attention to key features and providing a visually interesting (yet still unobtrusive) background. You can also reproduce colorful photographs on a transparency and have good resolution.
- They can be informal if necessary. For an impromptu meeting with colleagues, you can simply hand print or hand draw your transparencies.
Disadvantages of using overhead transparencies
- The projector may not be very good. Because overhead transparencies are the most popular visual aid, the equipment takes a beating. You’ll often find projectors that don’t focus well, have dim bulbs, or have no bulbs at all. That’s why I carry my own projector for local presentations. When I travel, I insist in advance on a good projector. Then, when I arrive at the place for my presentation, I go immediately to the projector and try it out. If it’s not good, I try to get another one.
- The bulb can burn out. Many of today’s projectors have a spare bulb built in, but sometimes the spare is burned out, too. Presenters who have a bulb burn out switch to the spare and go on. They usually forget to tell the visual aids people that the overhead is now down to only one good bulb. If that one burns out, you’re left with none.
Many speakers consider the overhead transparency their first choice of visual aid unless they have a good reason not to use it. But there are many good reasons to use other visual aids, either separately or in conjunction with overhead transparencies.
