Viewfinder Optics Part II

Viewfinder Information Displays

In most digital single-lens reflex cameras, the viewfinder does not only show the preview of the scene, but also additional information on current settings of the camera. Of course, all configurations can always be displayed on the main display of the camera, but these on-viewfinder screens summarize the current settings so that a photographer will not have to take his eye from the camera in order to check the configurations. For most entry-level cameras, this viewfinder information is usually limited to indicators for basic settings and therefore can be displayed with a single, horizontal display strip beneath the preview screen. Conversely, for most pro-level cameras, viewfinder information is so extensive that a second, vertical display strip is applied laterally to the preview screen. The image below illustrates the viewfinder of a Canon EOS 1Dx DSLR camera. The two displays mentioned are marked in green.

Viewfinder Screen All Info

Looking at the technical implementation of these viewfinder screens, these usually consist of Liquid Crystal Display (LCD) panels applied to the lower part of the viewfinder system. The LCD panels are translucent and therefore need to be backlit with LEDs. Although the LCDs have to be in the focal plane for a sharp projection of the information, these LCDs cannot be directly adjacent to the focusing screen for reasons of space. In order to place them in a position equivalent to the focal plane, they are applied to the pentaprism sideways with a short distance. The image below shows the position of both the vertical LCD (V-LCD) and horizontal LCD (H-LCD).

Viewfinder Information Screens

The LCD panels are optically connected to the viewfinder system by tiny prisms, deflecting light from the LCDs to the lower pentaprism surface, directed towards the eyepiece. All information on the viewfinder displays is also flipped horizontally and vertically as they get corrected automatically when travelling through the pentaprism. The figure below illustrates the projections of light from the LCD panels towards the eyepiece.

Viewfinder LCD Screens

 

Eyepiece

The eyepiece represents the optical system at the end of the viewfinder’s optical path designed for the photographer to observe the viewfinder image. It is an opening at the back of the camera where light from the viewfinder optics exits the camera to enter the photographer’s eye. To protect the sensitive eye from the solid material of the camera, an interchangeable eyecup made of soft rubber material is usually applied to the eyepiece, surrounding the opening.

The eyepiece not only consists of the visible opening at the back of the camera, but also includes lenses of various concave and convex curves. These lenses can be adjusted for nearsightedness and farsightedness of the photographer, referred to as dioptric adjustment. Furthermore, these dioptric adjustments are also often required for eyeglass wearers. Depending on the camera model, a dioptric adjustment dial is attached close to the eyepiece. Concluding it should be noted that diopter adjustments do not affect the focus circuitry of the camera as there is a separate auto-focus system. The diopter adjustment only affects how an eye perceives the image.

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