First Surface Mirrors - For Projection & 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. These mirrors are tough, robust, simple to clean and last many years. They make up nearly 100% of all mirrors manufactured.

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 major problem 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.

How to Purchase

As a specialised product, this item is not available through our on-line store and is only available by direct order from Acril Convex. As we deal with many international inquiries, we need your location including, country, city and or zip code. We also need to know how many you wish to purchase as this will alter the freight charges involved. Please contact us by email with your inquiry.

Product model: 20534 60cm First Surface Half Dome Mirror with Polymer Coating.

Cleaning & Maintenance

Handle the mirror only with plastic gloves to prevent fingerprints or marks. Remove surface dust with compressed air; photographic suppliers have pressure cans for cleaning of camera parts & lenses; these are ideal. Air supplied from motorised compressors may contain oil & contaminants. Never use paper towel or any abrasive on the mirror and definitely never rub/wipe any cloth or material onto the surface with any pressure. Marks may look unattractive but if they are not disturbing the projected image then you are better leaving the mirror as is. We have found the best way to clean is by 'flood cleaning' with a mild liquid detergent and warm water. The same solution that you would use to do the household dishes is fine - do not use anything that contains caustic or baking soda. Completely wet the surface with the solution and use a soft open weave cloth and very gently (use no pressure on the mirror at all) wipe the surface keeping a film of detergent between the mirror and the cloth. Let the solution dissolve and wash away the marks but don't rub or bear down on the mirror. Complete the process with warm clean water to rinse & remove traces of detergent. (Distilled water is best and will dry clear) Most of the water will bead off the mirror but give the mirror a shake to assist removal. Finally use compressed air or a hair dryer to dry out any remaining droplets. Some water marks may appear but usually these can be removed by a second clean or by very carefully and gently dabbing the spots with a micro fine cloth before they dry. Never rub or wipe the mirror surface using physical pressure.

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.

http://paulbourke.net/

http://paulbourke.net/exhibition/domeinstall/