Prism finder
A prism viewfinder is an optical component that is usually used in a ( single -lens) reflex camera . It allows that through the lens upside-down and through the oscillating mirror laterally reversed image through a parallel arranged to the optical axis of the lens eyepiece on the focusing screen to look laterally correct and upright. This makes the intuitive selection of the image section easier than with the light shaft finder . In addition, a higher image brightness can be achieved with the prism viewfinder.
history
Jenő Dulovits patented the first SLR viewfinder for viewing at eye level with a laterally correct, upright image in Hungary on August 23, 1943 - with the Duflex, he also designed the first 35mm SLR camera for this viewfinder, which is common today - however He did not yet use a roof prism, but individual prisms / mirrors. The introduction of the prism finder was decisive for the worldwide success of the single lens reflex camera concept.
The prism viewfinder consists of the following components
Note: In most SLR cameras, the prism viewfinder is an integral part of the camera and built into the camera housing . In cameras with an interchangeable viewfinder, the focusing screen is either part of the prism viewfinder or part of the camera, depending on the camera model, so in this case it cannot be removed together with the viewfinder.
functionality
In a single-lens reflex camera, the viewfinder image is generated by the light falling through the lens into the camera. There it is projected from a deflecting mirror at a 45-degree angle onto a ground glass, which is arranged horizontally above the deflecting mirror. The roof prism sits above the ground glass and mirrors the viewfinder image along the vertical axis (i.e. swapped left for right) and tilts it from the horizontal to the vertical. On the back of the camera, i.e. behind the prism , sits the viewfinder eyepiece, a lens system that ensures that the viewer can see the viewfinder image clearly.
Special designs
AE (Auto Exposure) viewfinder
A prism viewfinder with a built-in light meter . It allows an SLR camera to be upgraded with a TTL exposure meter. Often used with medium format cameras . With some camera models, an AE viewfinder extends the basic housing not only with the function of exposure metering, but also with automatic exposure.
Sports seeker
A prism viewfinder with a particularly large eyepiece that allows you to focus on the subject even if you do not hold your eye directly to the eyepiece. Some sports viewfinders allow you to look either from behind or from above by rotating the eyepiece. A subspecies of the sports viewfinder is the high-eyepoint viewfinder , which is tuned in such a way that even people who wear glasses can see the entire field of view, although their eyes cannot reach the eyepiece through the glasses. The Nikon F3-HP is a typical example of a camera with a high-eyepoint viewfinder .
Porro prism finder
With a pentaprism viewfinder, the viewfinder eyepiece sits directly behind the prism in the optical longitudinal axis of the camera. A Porro prism viewfinder deflects the viewfinder image from the focusing screen via a series of optical prism elements to an eyepiece that is located on the left edge of the rear of the camera. The advantage of this type of construction is a more compact camera housing and greater freedom of design. The camera manufacturer Olympus has installed the Porro prism viewfinder in the digital SLRs E-300 and E-330 . Porro prism finders are always built into the camera housing.
Penta mirror viewfinder
Unlike the pentaprism viewfinder of Penta mirror viewfinder uses a prism of glass, but with an array of mirrored surfaces. The functionality is otherwise the same. In comparison, the penta mirror viewfinder produces a somewhat darker viewfinder image than a pentaprism viewfinder. It is lighter and significantly cheaper to manufacture. It is often installed in inexpensive SLR cameras.