Pentaprismajärjestelmä

Pentaprismajärjestelmä refers to a specific optical system that utilizes a pentaprism. A pentaprism is a type of optical prism that contains five reflecting surfaces. Its primary function is to deviate a beam of light by a fixed angle, typically 90 degrees, while also producing a reflected image that is erect and laterally reversed compared to the original object. This unique characteristic makes pentaprisms highly valuable in optical instruments where precise image orientation is crucial.

In a pentaprismajärjestelmä, the pentaprism is integrated into a larger optical path. This system is commonly found in single-lens reflex (SLR) cameras. In an SLR camera, light enters the lens and is reflected upwards by a mirror onto a focusing screen. The pentaprism then takes the image from the focusing screen and redirects it, inverted and reversed, through the viewfinder eyepiece to the photographer's eye. This allows the photographer to see an erect and correctly oriented image of what the lens is capturing, despite the initial inversion and reversal caused by the mirror and focusing screen. The pentaprism effectively corrects these inversions, providing a direct view of the scene.

The geometry of the pentaprism is such that it achieves this image correction through a series of internal reflections. Light entering the prism strikes multiple surfaces, with each reflection contributing to the final orientation of the image. The accuracy and stability of the pentaprism's performance are critical for the usability of optical instruments like SLR cameras, ensuring that the photographer's view accurately represents the final photograph. While other prisms can deviate light, the pentaprism's ability to simultaneously correct for both vertical and horizontal reversal is its defining feature.