Pentamirror

A pentamirror is an optical component used in some single-lens reflex cameras to form the viewfinder image. It consists of a set of five flat mirrors arranged to fold and direct light from the camera’s focusing screen up to the eyepiece, producing an erect, laterally correct image for the photographer.

In an SLR, light from the lens is reflected by the reflex mirror into the focusing screen. The image on the screen is then reflected through the pentamirror assembly, which uses multiple flat mirrors to guide the light to the viewfinder. The design is compact and lightweight, making it a cost-effective alternative to a traditional solid pentaprism.

Advantages of the pentamirror include lower production cost, reduced weight, and a smaller overall camera size, which suits entry-level and compact SLR designs. It enables viewfinder systems in consumer-focused cameras without the expense of a full pentaprism assembly. Disadvantages include reduced brightness and contrast in the viewfinder, due to additional reflections and less efficient light transmission, as well as tighter tolerances required for alignment and cleaner optics.

Compared with a pentaprism, a pentamirror typically offers a dimmer viewfinder and sometimes less uniform illumination, but it remains a common choice in budget-friendly DSLRs and some bridge cameras where affordability and weight are prioritized over maximum viewfinder brightness. While not as widely used in professional-grade bodies, pentamirror technology continues to balance performance with cost in lower- and mid-range cameras.