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A first-surface mirror or front-surface mirror (also commonly abbreviated FS mirror or FSM) is a mirror with the reflective surface being above a backing, as opposed to the conventional, second-surface mirror with the reflective surface behind a transparent substrate such as glass or acrylic.
Historically, the bronze mirror, an FSM type, was standard from ancient times until relatively recent centuries. These were simply highly polished pieces of
A first-surface mirror or front-surface mirror (also commonly abbreviated FS mirror or FSM) is a mirror with the reflective surface being above a backing, as opposed to the conventional, second-surface mirror with the reflective surface behind a transparent substrate such as glass or acrylic.
Historically, the bronze mirror, an FSM type, was standard from ancient times until relatively recent centuries. These were simply highly polished pieces of bronze
Bronze is an alloy consisting primarily of copper, commonly with about 12–12.5% tin and often with the addition of other metals (including aluminium, manganese, nickel, or zinc) and sometimes non-metals, such as phosphorus, or metalloids such ...
or other metals, usually small and round, and designed for a person to see their face.
First-surface mirrors are now made for applications requiring a strict reflection without a ''ghosting'' effect as seen with a second-surface mirror, where a faint secondary reflection could be observed, coming from the front surface of the glass. This includes most optics applications where light is being manipulated in a specific manner. Reflecting telescopes, rear-projection televisions, periscopes, non-reversing mirror
A non-reversing mirror (sometimes referred to as a flip mirror) is a mirror that presents its subject as it would be seen from the mirror. A non-reversing mirror can be made by connecting two regular mirrors at their edges at a 90 degree angle. ...
s, high-quality kaleidoscopes, and the animation process.
In cases where the mirror is subjected to extreme cold (as low as 33 K as in the James Webb Space Telescope
The James Webb Space Telescope (JWST) is a space telescope which conducts infrared astronomy. As the largest optical telescope in space, its high resolution and sensitivity allow it to view objects too old, distant, or faint for the Hubble Spa ...
), a polished pure beryllium mirror is used without a first-surface coating in order to eliminate deformations caused by differing coefficients of thermal expansion.
Silvering
The " silvering" on a front-surface mirror is usually aluminium for visible light and gold for infrared radiation.References
Mirrors {{optics-stub