What is a Slide Projector?

A slide projector is a device, which is used to view photographic slides. It consists of four main parts, which are as follows:

• A fan-cooled electric light bulb or other light source
• A reflector and "condensing" lens to direct the light to the slide.
• A holder that would support the slide.
• A focusing lens.

Often a flat piece of heat absorbing glass is put in the light path between the condensing lens and the slide so that the slide is not damaged. The glass transmits visible wavelengths but it certainly absorbs infrared. Light passes through the transparent slide and lenses as a result of which the visible image is enlarged and projected onto a perpendicular flat screen and the audience can view its reflection. The other way of doing it would be to project the image onto a translucent "rear projection" screen, which is often used for continuous automatic display for close viewing. This form of projection also helps in avoiding the audience's interrupting the light stream or bumping into the projector. In the 1950s and 1960s the slide projectors were a common form of entertainment. It was time when family members and friends would gather to view slide shows. Low cost paper prints, digital cameras, DVD media, video display monitors and digital projectors have replaced the In-home photographic slides and slide projectors to a large extent.

Types of Slide projectors and their Operating Tips
There are many kinds of slide projectors and each one uses a different technology.

• The Carousel slide projectors have circular trays, which consist of 20 to 140 slide holders. A stepper motor rotates these trays, and another corresponding system drops each slide in front of the light bulb to be projected. The trays can be horizontal or upright, though horizontal trays are more frequently seen.
• In case of Dual slide projectors, these have a number of holder trays that are made up of an inner and outer ring. Every ring can be advanced and can be put in independently and they can also be locked together. Two or more slides can be put in and they can be projected simultaneously.
• Unlike Dual slide projectors, Single slide projectors have only one holder slot that is built into a compact case, which also contains the bulb and lenses. These projectors can project only one slide at a time. Every time the slide has to be removed and loaded manually. The slides are generally compact and can be carried conveniently to any place. They are often more in tune with larger slide formats.
• Viewer slide projectors display slide images on built-in viewing screens and the holders along with the projection mechanism are contained in a case behind the screen. The screen can be used for previewing images before they are projected onto a bigger screen.
• Slide cube projectors are called so as they have cube-shaped holders where slides are stacked in uniformly one on top of the other. Each slide is put into a circular plate and projected onto a preview screen before it is enlarged and one might include up to 40 cubes, each holding 36 to 44 slides.
• The other type of projector is the Stereo Slide projector which can project two images at a time and that can be from single holders or separate holders. There is a polarizing lens in front of the slides, which projects every image with a different polarization. As a result of which the image that comes up is three-dimensional and we get a more detailed picture than a single slide image.

Tips to follow when buying a Slide Projector
When buying a slide projector there are two things that have to be considered.

• Slide Projector Lamp or light bulbs- Always one such projector should be chosen that has a halogen or LED light bulb so that they don’t burn out very soon. One thing that has to be made sure is that these bulbs should not get overheated when used for long. If you can buy one, which also has the cooling fans to regulate the bulb temperature, then that is the best option.
• Focus-The other important thing is the Focusing ring or button so always a projector with a simple focusing ring or button should be chosen that would allow you to adjust the image and would not require repositioning of the entire projector. Amongst features, look for one that allows adjustments in size, sharpness, color and contrast.

So if you still interested in this piece of the old world charm, buy it but keep these simple guidelines in mind so that you can buy a good slide projector which is low cost and also has lower maintenance charges.