Projector
Introduction
A projector is an optical device that projects an image (or moving images) onto a surface, commonly a projection screen. Most projectors create an image by shining a light through a small transparent lens, but newer types of projectors can project the image directly, by using lasers. A virtual retinal display, or retinal projector, is a projector that projects an image directly on the retina instead of using an external projection screen.
History
The earliest projectors were essentially the camera obscura, a device dating back to antiquity, and the magic lantern, which used lenses and a light source to project images from glass slides onto a wall. These evolved into slide projectors and the overhead projectors popular in schools and businesses for many decades. The advent of digital technology saw the development of digital projectors, which have largely replaced their analog counterparts.
Types of Projectors
There are several types of projectors available today, each with their own advantages and disadvantages.
Slide Projector
A slide projector is an opto-mechanical device for showing photographic slides. Slide projectors were widely used in the mid-20th century in educational and other institutional settings. Personal use of slide projectors was also common in the 1950s and 1960s but declined as other technologies became more affordable and easier to use.
Overhead Projector
An overhead projector (OHP) is a variant of slide projector that is used to display images to an audience. The overhead projector was once a common feature of classrooms and business meetings, but it has been replaced by the digital projector in both of these settings.
Digital Projector
Digital projectors project a digital image by a variety of means, the most common being by the use of a metal-halide light source which reflects off of a DMD (Digital Micromirror Device) chip. The light is then reflected onto a screen, creating the image.
Laser Projector
Laser projectors use lasers as the light source to create the image. Laser projectors have advantages over traditional digital projectors: they are capable of projecting more vibrant colors, have a longer lifespan, and allow for thinner, lighter projectors.
How Projectors Work
Projectors work by using a beam of light and a lens system to project images onto a screen. The image to be projected is created either by blocking some of the light from reaching the screen (in the case of slide and overhead projectors) or by digitally creating an image and using light to project it (in the case of digital and laser projectors).
Light Source
The light source in a projector is typically a lamp, but in newer projectors, lasers are used. The light from the source is reflected off a series of mirrors and through a lens, which focuses the light onto the screen.
Image Creation
In slide and overhead projectors, the image is created by blocking some of the light. In digital projectors, the image is created digitally, either by an LCD screen or by a DMD chip. In laser projectors, the image is created by modulating the laser light.
Projection
The light from the projector is focused onto the screen by a lens. The size of the image can be adjusted by changing the distance between the projector and the screen or by adjusting the zoom on the projector.
Applications
Projectors are used in a variety of settings, from classrooms and conference rooms to home theaters and large events. They are also used in some types of scientific research and in planetariums.
Education
In educational settings, projectors are used to display images, text, or video to a large group of students. This can be more effective than having each student look at a book or a computer screen.
Business
In business settings, projectors are often used in meetings and presentations. They allow the presenter to display information to a large group of people at once.
Home Theater
Many people use projectors in their home theaters. A projector can create a much larger image than a television, providing a theater-like experience at home.
Events
Projectors are often used at events such as concerts and sporting events. They can be used to display live video of the event, or to show information or advertisements.
Scientific Research
In some types of scientific research, projectors are used to display images or data. For example, in astronomy, projectors are often used in planetariums to display images of the night sky.