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First Surface Mirrors

Projection and Planetarium Applications

Your normal every day mirror is manufactured so that the reflective coating is deposited onto the rear side of a clear substrate (usually glass or plastic) and protected with a backing paint on the rear. These are 2nd surface coated mirrors. They are perfect for every day applications as the clear substrate protects the reflective coating from any damage. The rear side is also protected by the backing paint to prevent scratching and oxidising of the fragile reflective surface.

First surface mirrors, as the name implies, has the reflective coating on the first surface (top exposed surface) of the mirror. This reversal is necessary whenever a mirror is to be used to project an image onto a screen. If you use a normal mirror to project an image, the light rays must travel through the clear substrate before reflecting back through the material so as to project an image. This causes a "ghosting" effect, as the light rays will be reflected twice at slightly different angles (caused by the thickness of the substrate). When an image is projected onto a screen the observer will see the main image (from the reflective coating) and also a secondary and duller image caused by reflection from the top surface of the substrate. This makes the process unsatisfactory for projection work. By placing the reflective coating on the top of the substrate, no secondary image can occur and the result is a sharp precise reproduction.

Since the reflective coating is now exposed to the physical world, proper care and handling is absolutely essential. The surface is soft and absolute care is required at all times if the mirror is to remain in its original state. To help protect the surface we apply a polymer coating to the surface which provides an air barrier but this is not a physical barrier as such. The less the mirror is handled, the better. Treat a first surface mirror as you would a delicate instrument and a long life will be obtained.

DuraVision™ First Surface Mirrors

First surface mirrors are fragile and difficult to manufacture, they require specialist skills to achieve a true and accurate reflective image. If you are developing products requiring first surface mirrors we would like to discuss your ideas. We regularly work with other manufacturers to provide products which include mirror components. Our experience in manufacturing in this difficult field means your project will benefit from time savings, fresh ideas and and high quality final product.
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University of Western Australia

Paul Bourke from the University of WA is the designer of projection systems employing first surface mirrors of a hemispherical shape and it is through his efforts that an affordable alternative to expensive projection lenses is now a reality. We gratefully acknowledge his work in this field and refer you to him for details on methods and precise technical information. Please see the following links for additional information, more pictures and installation methods.