How does a Front Surface Mirror help a Rear Projection System?

Rear projection systems ideally use a front surface mirror (or first surface mirror) instead of a second surface mirror for image clarity.

Image clarity is often determined by taking into account two primary indicators. Amount of ghosting is the first and is a condition where an image is displayed two or more times with the secondary images being offset on the display. The secondary images typically have a decreased intensity. In the case of the use of a second surface mirror the ghosting images are at about one tenth of the intensity of the primary image when the angle of incidence is around 65 degrees.

The second indicator is contrast. This is measured as the minimum light intensity level in the image subtracted from the maximum light intensity level. This is then divided by the maximum light intensity level added to the minimum light intensity level. In essence this means that a projected image with an effective minimum light intensity level of zero and a maximum light intensity level higher than zero will have a contrast ratio of one. As the minimum intensity level becomes brighter, the image’s contrast level decreases and the overall picture quality decreases. If the minimum and maximum levels are the same value, then the contrast is zero and the image will look washed out.

With a first surface mirror, only the aluminum surface on the front of the mirror reflects the incident light. This means that any ghosting produced by the mirror is entirely eliminated and the contrast ratio of the incident light is unaffected by the reflecting surface.

For more information about first surface mirrors and their benefits in rear projection systems please call 800.426.2864 or email us.

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This entry was posted by ZC&R, on Monday, June 22nd, 2009 at 5:00 am and is filed under Optical Applications, Optical Coatings. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response below.