DD146509A1 - OPTICAL ARRANGEMENT FOR AUTOMATIC OR SEMIAUTOMATIC SHARPENING FOR MIRROR REFLECTION CAMERAS - Google Patents

Abstract

The invention relates to an optical arrangement for automatic or semi-automatic focus adjustment for SLR cameras with Pentadachkantprisma and arranged in the viewfinder beam path in the Schaerfeebene Meszkeilen. The object of the invention is to provide an optical arrangement for automatic or semi-automatic focusing, which operates on the Auslektungsprinzip and avoids complicated special receivers and partially transparent optical means. According to the invention, behind the image-elevating mirror surface of the roof prism, there are two optical imaging systems with widely advanced main planes, with the aid of which an image plane lying in front of and behind the actual plane of the plane can be imaged. The image is taken on two out of the mirrored area arranged Fotoempfaenger, for example, photoresistors, which are arranged in bridge circuit and whose non-linear characteristic is used for automatic focusing. In the balanced state, a picture with gleichmaesziger blurs on both Empfaengern.

Description

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Title of the invention

Optical arrangement for automatic or semi-automatic focusing for SLR cameras

Field of application of the invention

The invention relates to an optical arrangement for automatic or semi-automatic focus adjustment for SLR cameras with Pentadachkantprisma and two iia viewfinder beam path in the focus plane arranged Meßkeilen, which are adjacent with opposite slope.

Characteristic of the known technical solution e n

For focusing photographic SLRs, it is known to arrange two receiver areas with a plurality of adjoining photoelements in the beam path of the objective, namely in an equivalent focal plane to the film plane or viewfinder plane generated by optical means. The image splitting on the two areas is carried out with two measuring wedges arranged opposite to each other. For focusing, the brightness levels are opposite. gender of each other associated photo elements compared. If the brightness is the same, then the lens is in focus. The setting is fully automatic or semi-automatic to an extreme signal ₀

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Another known device has a Zwischenabbildurigsoptik with strip - double wedge, which splits the imaging beam path into two aperture areas and separately arranged, strip-shaped subdivided photoreceptors feeding, with a brightness comparison of the stripes on the photoreceptors done in pairs. Again, the setting is made to extreme value when equality prevails on the Streifenpaa.ren.

In both cases, optical arrangements are used in which the beam path for focusing by the reflecting mirror is directed downwards via an auxiliary mirror articulated to the latter to the camera base. In a further embodiment of the first known principle, the bildaufrichtende surface of the Pentadachkantprismas is designed to be partially transparent, with a direct mapping of arranged in the viewfinder image wedges on the receiver areas.

In the known arrangements described herein, the image plane is sharply imaged over two opposite aperture areas of the objective by suitable optical means on the receivers. As a receiver strip-like subdivided arrangements or several closely juxtaposed photo elements on receiver areas are required. Such receivers are usually expensive special designs, which also require a relatively high circuit complexity. In addition, for the Ausspiegelung of the beam path for focusing partially transparent surfaces in the recording or viewfinder beam path are arranged, which cause a reduction in the viewfinder Bright ·

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Object of the invention

The present invention is intended to avoid the mentioned disadvantages, namely the use of complicated special receivers and the reduction of the viewfinder brightness by partially permeable coatings. "

Explanation of the essence of the invention

The invention has for its object to provide an optical arrangement for automatic or semi-automatic focus, which operates on the Auslektungsprinzip.

According to the invention, the object is achieved in that behind the bildaufrichtenden mirror surface of the roof prism two optical imaging systems are provided, with the aid of one before and one behind the actual focus plane image plane is mapped »Conveniently, the image is on two outside the mirrored region of the mirror surface arranged receiver , which are preferably effective to the right and left of the: mirror surface. An essential feature of the invention further consists in that the resulting in the measuring wedges viewfinder sectional image is imaged in the balanced state with uniform blurring. In a further embodiment of the invention are as a receiver photoresistors, which are arranged in bridge circuit, provided, in which the non-linear characteristic is utilized for automatic focusing.

Embodiment . ,

The invention will be explained in more detail below using an exemplary embodiment.

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Show it:

Pig, 1 the characteristics of the potoresistors E ₁ and E _?

Pig. 2 a) Side view of the Pentadachkantprismas and to order the Ausspiegelung

b) Front view of the pentachragon prism with arrangement of the imaging systems and receiver

According to Pig. 2, two photoreceivers E 1, E _{2 are arranged} separately to the right and left of the mirror surface 4, viewed in the light direction, behind the image-revolving surface of the pentadach prism 3. The len of the individual Meßkei of Meßkeilpaares 5 beam paths are directed to the front of the respective photoreceptor E-, Ep optical imaging system 1, 2. The imaging systems are arranged in such a way that imaging planes, which lie in front of and behind the wedge crossing point, ie the exact viewfinder image plane, are displayed sharply. This results in coincidence setting on the photoreceptors E ₁ , Ep uniformly blurred images that lead to the same signal displays. Using . of photoresistors as a photoreceiver in bridge circuit resulting in focus setting same resistance values, so that the control circuit is de-energized. If one uses the photoreceivers E ₁ , Ep in a parallel circuit, then the same signal currents result as a criterion for the completed Objektiwerstellung,

The focus is thus completed when the images shown are imaged with uniform blur and have no signal difference.

If, for example, according to FIG. 1, a sharp image of the image plane, which lies before -4s ^{1 in} front of the exact viewfinder image plane, on which photo receiver E ₁ , then flows

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a photocurrent I ^. On the Potoempfanger E ₂ takes place with this setting a completely blurred image of the image plane, which is + Δβ * behind the exact viewfinder image plane. It flows here the photocurrent Ip. With the Pot © current difference ΔΙ- »I« - I * the control process for the automatic focusing takes place with the corresponding gain. With exact adjustment of the sharpness elevation in s', images of the image planes shifted by -Äs * appear on the photoreceptors E., and Ep equal blurred images. In this case, the photocurrent difference JI = 0, ie I ₁ = I ₂ ' for the photocurrents .

With manual adjustment of the lens for semi-automatic focusing, this photocurrent difference can also be used for a light indication of the setting state.

Due to the constructively defined positional difference of the image planes to the exact viewfinder image plane, a clearly defined directional dependence results for the automatic lens adjustment. The optical reflection principle according to the invention has the advantage that no light losses and impairments in the viewfinder image due to geometric or physical beam splitting occur. In addition, the automatic focus can be observed or checked directly in the viewfinder image. Since the image to be assessed is transmitted from the viewfinder plane to the photoreceivers and fed to an electrical evaluation unit, the method is independent of the lens focal length and aperture used.

Claims (1)

21 1 219 invention claim 1) Optical arrangement for automatic or semi-automatic focus adjustment for SLR cameras with Pentadachkant prism and arranged in the viewfinder beam in the focal plane Meßkeilpaar whose Meßkeile with opposite slope next to each other, characterized in that behind the Bildaufrichtenden mirror surface (4) of the Pentadachkantprismas (3) two optical imaging systems (1; 2) are provided, with the aid of which a lying before and one behind the actual focus plane BiId * level is mapped. 2) Optical arrangement according to item 1, characterized in that the optical imaging systems (1, 2) have far advanced main planes. 3) Optical arrangement according to item 2, characterized in that the images on two outside the mirrored region of the mirror surface (4) arranged Potoempfangern (S ₁ , E ₂ ) take place, which are preferably attached to the right and left of the mirror surface (4). 4) Optical arrangement according to point 2, characterized in that in the Meßkeilpaar (5) resulting Sucherschnittbild in the balanced state with uniform blurring on the photo receivers (E .., Ep) is displayed » 5) Optical arrangement according to item 4, characterized in that as a photoreceiver (E ₁ * E ₂ ) potoresistors 217 219 are provided in bridge circuit, in which the non-linear characteristic is used for automatic focusing. For this ... 2 pages drawings- '