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Overhead Projector

Optics
by

Kiera Kaminski

on 1 November 2012

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Transcript of Overhead Projector

Overhead Projector Benefits of the overhead in classrooms The overhead projector is an easy low-cost interactive environment for teachers and students. Teaching materials can be pre-printed on plastic sheets, which then they can directly write using a non-permanent, washable color marker. This saves time, since the transparency can be pre-printed and used many times, rather than having materials written before each class. The overhead is is usually positioned at a comfortable writing height for the teacher and allows them to face the class, providing better communication between the students and teacher. The enlarging features of the projector allow the teacher to write in a comfortable font size and in a natural writing position rather than writing in an overly large font on a blackboard and having to constantly hold their arm out in the air to write on the blackboard. Light and Projector Sheets:
- main component of the overhead projector is the base
- contains a clear glass top, an interior light, a small fan and a vent
- the fan on the back of the unit removes the heat that is produced by the light and out through the vent, this prevents the projector from overheating
- when the light is turned on the only light escaping is through the glass top, this illuminates the glass top and anything placed on top of it
- the clear plastic sheets let light shine through the sheet to project an image Adjustable Arm and Head:
- an adjustable arm and head is attached to the base of the projector
- head of the unit contains a mirror and two lenses on the front and side
- the mirror is positioned so that it can reflect light coming in through the bottom lens
- when the light in the base is turned on it projects the image off the mirror and onto screen Mirror Positioning:
- moving the arm up or down will affect both the focus and the size of the image projected
- the angle of the projector head allows the projected image to be moved as needed
- it needs a few moments after adjustment to get the projected image to focus on the screen Lights : Most overhead projectors use a high-powered halogen lamp that may consume up to 750 watts yet produces a fairly dim, yellow image.
- The light is an important part to the function of the head
- The light necessary for the lens to detect the transparencies and darker print Mirrors:
-The mirrors in the head of the unit work together to reflect light and project an image onto a screen
- The 1st mirror works to capture the light from the base of the projector. The light from the mirror is then reflected to the 2nd mirror
- The 2nd mirror reflects the light through a magnifying lens for a larger projection Magnifying Lens:
- First the mirrors have to reflect the light towards the screen, the image would be small without the magnifying lens
- The lens captures the image reflected by the mirror and shines it on the screen so that it is longer and more legible
- The clarity of the image depends on how close the lens is to the transparent sheet and how close the projector is to the screen Breaking It Down: How It Works: By Kiera Kaminski and Jenna Van Huisstede October 2012 Light Source Lens Mirror Surface P Disadvantages: - for a large classroom of people to see items clearly the projector must be at the right distance and angle
- overhead projector light bulbs are costly, and average cost of $300
- overheads are very large and bulky and can be difficult to move around to other classrooms
- outdated technology, today we have more advanced, better quality overhead projectors
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