Front Surface Mirror Vs Back Surface Mirror

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 in cases where the mirror is subjected to extreme cold as low as 33 k as in the james webb space.

Front surface mirror vs back surface mirror.

Because left and right are defined relative to front back and top bottom the flipping of front and back results in the perception of a left right reversal in the image. In most cases the substrate is glass and the aluminum based coating has a protective coating over it that helps to protect it from damage it might receive during transport or installation. Each mirror ships with a protected film over the coated surface. A mirror s substrate surface should be flat and smooth.

A mirror typically reverses the forward backward axis. To be precise it reverses the object in the direction perpendicular to the mirror surface the normal. We can make front surface mirrors out of several ultra pure metals see here for specification which is evaporated under carefully controlled conditions in a high vacuum chamber which contains the selected substrate to be coated. An important part of mirror technology is providing a durable front surface mirror that is stable and can be cleaned.

Usually first surface mirrors also have a very thin often under 1 micron thick protective clear coating on top of the metal layer. First surface mirrors are reflective on the front. The flatness is usually specified in terms of how many wavelengths of light the surface deviates from being a perfect plane. The reflectivity of the front surface mirror is much higher than for the rear surface mirror thus greatly improving the efficiency of the system.

These mirrors use glass as a protective surface and have the mirror coating commonly referred to as silvering on the back side or second surface. A good example of a first surface mirror is polished stainless steel. A back surface mirror has the reflective coating on the surface opposite the viewing surface so it s imperative that the substrate be transparent. How are they made.

Rectangular first surface mirrors are ideal for applications requiring the mirror to be mounted at 45 in order to produce a 90 bend in the light path. The exposed glass helps protect the mirror coating underneath from scratching or degradation due to environmental factors such as weather fingerprints and dust. The mirrors are available in circular square and rectangular dimensions.