DE2152790C2 - Optically effective reflective setting screen for a single lens reflex camera - Google Patents

Description

; The invention relates to an optically effective reflective adjustment screen for a Mirror reflex camera of the type specified in the preamble of claim 1. With one through the DE-PS 9 33 132 known SLR camera of this type is the reflector of the steps

_Ί spherical active flanks formed, between which in section vertical, ring-shaped circumferential interference flanks lie. This step mirror accordingly forms a flat approximation of a spherical hollow mirror and it acts like a field lens and increases the brightness of the viewfinder image as a result of the pupil imaging. Due to the mirror arrangement of such a reflex camera, however, the pupil imaging cannot take place in the optical axis of the objective or of the adjustment screen formed by the active flanks of the step reflector. Rather, the pupil imaging must take place from a point which is laterally adjacent to the optical axis to a point which is just as far away from the optical axis on the opposite side. This inevitably results in the known optical imaging errors of oblique bundles, and these imaging errors inevitably lead to brightness losses. In the known case, the distortion of the viewfinder image should be avoided by means of an eccentric design of the mirror. The brightness of the viewfinder image, ie the pupil image, however, remains unaffected by this. The invention is therefore based on the object, the viewfinder image using a simple structure. th, flat reflector adjustment screen thereby to be uniformly bright that the errors of oblique bundles are largely eliminated when the pupils are mapped onto one another.

The problem posed is achieved by the features specified in the characterizing part of claim 1. This arrangement ensures that two focal points are created which are located on both sides of the optical axis of the objective at the point of the pupil to be imaged or imaged, so that an optically perfect pupil image can be achieved in the manner of an ellipsoidal reflector with practically no loss of brightness.
Reflectors in the form of parts of ellipsoids of revolution and their properties have been known for centuries. They found and are used to transmit optical but also acoustic signals from one focus to the other. The invention is based on the knowledge that this reflection principle, which has long been known, can be used with particular advantage for pupil imaging in single-lens reflex cameras of the specified type, in order to give the viewfinder image maximum brightness. The production of the adjustment screen designed according to the invention can, however, be carried out in a simple and inexpensive manner by conventional techniques in the Matrizenpreßverfahran.

The fact that the active surfaces run in the shape of a circular ring results in a geometric shape Completely new structure in which the focal points of the circular active surfaces are relatively far from the Axis can be distferm and distributed over the surface result in even reflections that create a Ensure optimal viewing of the viewfinder image.

The features of claim 3 achieve

that there is a certain light scattering that the

Let transitions between active flanks and interference flanks of the Fresnel surface disappear, with an optimal Focusing of the viewfinder image is guaranteed.

DE-PS 9 68 653 roughening the active flanks of a spherical setting screen already known for photographic cameras.

Exemplary embodiments of the invention are described below with reference to the drawing. In the Drawing shows

F i g. 1 is a schematic sectional view of a reflex camera;

F i g. 2 is a perspective view of a concave mirror for point-by-point reflection, which represents the state of the art;

F i g. 3 is a perspective view of a spherical Fresnel mirror, which works in principle like the concave mirror according to Fig.2 and also the state of Technology represents-,

F i g. 4 is a perspective view of an ellipsoidal shell structure; how the principles of the invention are to be explained;

F i g. 5 shows an adjustment screen designed according to the invention with concentric elliptical active flanks;

6 shows a perspective, partially sectioned view of an adjustment screen designed according to the invention with concentric circular active flanks;

FIG. 7 is a plan view of the setting screen according to FIG. 5;

FIG. 8 is a plan view of the setting screen according to FIG. 6;

9 shows a perspective, partially sectioned view of the known Fresnel mirror according to FIG. 3;

Fi g. Figure 10 is a partial perspective view of the surface the effective flanks of the setting screens according to Fig. 5 and 6.

F i g. 1 shows a reflex camera 10, the lens 14 with shutter in a front housing part 12 16 and cover 15 upwards, and a trigger 18 carries. There are two finer in this housing part Squeeze rollers 20 and 22, which are used in this camera, which is designed as a self-development camera of the exposed film units.

The reflex camera 10 has a carrier 24 for a film cassette 26. The camera body will completed by a sloping rear top wall 28 which supports a viewfinder mirror 30 inside and a front wall 32 connected to the rear wall 28 and supporting the viewfinder 34 therewith. the The film cartridge 26 disposed within the carrier has an integrally formed lip 40. The on The furthest forward-facing end of the film cassette 26 has a withdrawal slot 42 which faces the inlet the two nip rollers 20 and 22 are aligned.

The uppermost film unit 46 of the cassette 26 is located in the exposure plane 44. Each film unit 46 has a photosensitive sheet 48 adjacent to a transparent sheet 50.

At one end of the laminate consisting of sheets 48 and 50 is a tearable container 52 attached with treatment liquid

According to FIG. 1 are the individual components the reflex camera 10 in the viewfinder. When the exposure is a cover plate 60 to a Axis pivoted into a position in which it rests tightly against the upper wall 28, as shown in FIG. 1 is shown in phantom

During the adjustment, the exposure plane 44 is covered by the cover plate 60, and this prevents light from impinging on the film unit 46. The cover plate 60 has on its underside Ribs 62 which fit over lip 40 of film cassette 26 to provide a light tight connection. The top surface of the cover plate 60 carries a reflective adjustment screen 64.

The setting screen 64 is the surface on which the lens 14 images the viewfinder image. A spring 65 acts against the top of the cover plate 60 and the underside of the top wall 28, whereby the cover plate 60 is pressed down and lies over the opening of the film cassette 26.

The reflex camera 10 is transferred to the exposure position by the cover plate 60 upwards is pivoted into the position shown in phantom. A magnet 67 fixed to the top wall 28 detects an anchor 69 fixed to the cover plate 60, whereby the cover plate 60 is in the exposure position is magnetically locked against the biasing force of the spring 65. A cover plate, not shown lies above the entrance opening 66 of the viewfinder 34 to prevent stray light from passing through to the film unit 46 the viewfinder 34 occurs when the exposure plane 44 is not covered by the cover plate 60.

The exposure mirror 68 is located on the underside of the cover plate 60. By pivoting the Plate 60 upwards, the exposure mirror 68 is brought into a position in which it is next to the viewfinder mirror 30 If the cover plate 60 is in the exposure position is locked, the exposure mirror 68 can light rays designed by the lens 14, reflect after the film 46, since the exposure plane 44 is no longer shielded

In the distance and image adjustment, the lens 14 is adjusted so that a real image of the The subject is focused on the setting screen 64. All the light that makes up the real picture generated, is reflected upwardly by the screen 64 and forwardly by the viewfinder mirror 30 and passes over

-, an entry opening 66 in the viewfinder 34. The light entering the viewfinder 34 is passed through a concave Reflects mirror 70, which provides an upright and laterally correct image of the subject. the Sharpness of the image generated in the viewfinder 34 is a

im direct indication of the sharpness of the photographic Image.

For purposes of illustration, it should be assumed that the lens 14 and the aperture 15 a middle distance setting

ι j form the optical path that passes through the optical axis 78 is characterized.

After reflection at the viewfinder mirror 30 the optical axis 78 runs in accordance with the setting screen 64. The light rays reflected from the setting screen 64, characterized by an optical axis 80 and they are the finder 34 via the same viewing mirror 30 and the immersion riffs opening 66 and a

'Prism 72 supplied and hit the concave mirror 70 on. The concave mirror 70 generates a real erect, laterally correct image of the subject and an eyepiece 74 enlarges the image viewed with the eye 82.

The lens 14 defines an exit pupil 84, the infoige of the viewfinder mirror 30 and the length of the

jo optical axis 78 with its pupil point at the point 86 appears to lie opposite the setting screen 64.

The adjustment screen 64 consists of a plurality of concentric reflective graded surfaces, which are described in detail below and occupy such a position that when the Exit pupil 84 lies with its pupil point at point 86, essentially all of the light that from the exit pupil 84 to the screen 64, via the viewfinder mirror 30 through the entrance opening

-to 66 and reflected after the entrance pupil of the viewfinder will.

The exit pupil 84 is imaged at the entrance opening 66. It can be seen that a bright image of the The focused image on the viewing screen 64 can be presented to the eye at the entrance opening 66 since the image reflected from the screen 64 is concentrated at the entrance opening 66. Instead, you can such a real image in the same way at a distant place, namely at the viewing point station 82, can be viewed through a viewfinder 34 which defines a new exit pupil by imaging the entrance opening 66 in the eye station 82. It can also be seen that light is reflected from the adjustment screen 64 to the entrance opening 66 without introduce a comatic error or an astigmatic error into the image of the exit pupil 84.

In the following, reference is made to FIG. Reference is made to Figure 2 of the drawing, which represents a prior art. Here, a spherically shaped concave mirror 88 is shown, the reflective surface 90 of which is opens upwards. This mirror is symmetrical about an axis 92, which acts as the optical axis for the mirror 88 A point light source 94 is located outside the reflection surface 90 and offset from the optical axis 92. In practice, this point light source 94 can be real or apparent Be source and it can e.g. B. correspond to an extended light source that is at the focal point of the

Lens is imaged.

A plurality of light rays 96 are shown exiting the point light source 94 and on the reflective surface 90 hit. As a result of the formation of the reflective surface 90 and the location of the Point light source 94 both in relation to this surface 90 and in relation to the optical axis 92 the light rays 96 impinging on the mirror surface 90 are reflected from here and in the vicinity of a point 98 collected. The position of the point 98 is therefore that of the point light source 94 with respect to the reflection surface and the optical axis 92 as well as by the properties of the surface 90 determined.

However, the focusing of the light beams does not happen exactly at point 98, since this causes the optical aberrations of oblique bundles result.

In addition, as a result of its geometry, the concave mirror 88 leads not only to the imaging errors, but also to komatic and astigmatic errors when the point light source 94 is imaged at location 98. These aberrations depend on the perpendicular distance between the point light source 94 and the optical axis 92.

In the following, reference is made to FIG. 3 of the drawing taken where the spherical concave mirror according to DE-PS 9 33 132 as a spherical Fresnel mirror 100, which is arranged symmetrically about an optical axis 102. With the Fresnel mirror 100, the imaging characteristics of the mirror 88 are obtained fairly accurately. If a real or Apparent point light source 104 is considered, which is squat outside of the mirror 100 to the optical Axis 102 lies, then light rays 106 emanating from the point light source 104 hit the reflective Surfaces of the mirror 100 and are imaged in the vicinity of a point 108. As with that spherical concave mirror 80 according to FIG. 2 becomes a comatic and an astigmatic aberration in the am Point 108 introduced image designed to an extent that is the perpendicular distance from the Point light source 104 depends on the optical axis 102.

In Fig. 4 are three mutually perpendicular axes with XX. YY and ZZ shown. A plurality of concentrically arranged ellipsoids 110, 112 and 114 have common focal points 116 and 118.

Ellipsoids 110, 112 and 114 have major axes that coincide with the YY axis and they have common minor axes that coincide with the X-X and ZZ axes.

One characteristic of an ellipsoid is that a line passing at any point on the surface in Normal direction, bisects the angle enclosed by those lines drawn by the Go out focal points of the ellipsoid and extend to the point of intersection of the line mentioned. If the concave surface of the ellipsoid is reflective, then all light coming from you will be Focal point hits the surface, reflected after the other focal point of the ellipsoid.

For example, if a point light source is viewed at focus 116 and it is assumed that the inner surfaces of ellipsoids 110, 112 and 114 are reflective, then it is clear that any Light impinging on the inner surface of one of the ellipsoids 110, 112 and 114 from point 116, after Focus 118 is reflected. This reflection is one perfect regardless of the point at which that

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b5 light emanating from the focal point 116 on the inner surface of the ellipsoids 110, 112 and 114 hits.

Consider now two pairs of parallel planes 120 and 122 that are sufficiently close to one another to approximate a single plane defined by the XX axis and the YY axis, respectively. If such a plane passes through the ellipsoids 110, 112 and 114, as shown in Figure 4, their intersections would form concentric ellipsoidal segments 124, 126 and 128, respectively. Because planes 120 and 122 are so closely spaced, ellipsoidal segments 124, 126 and 128 also lie in a single plane and appear as concentric ellipses when brought normal to the XXYY plane. If the planes 120 and 122 are sufficiently close to one another, then the ellipsoidal segments 124, 126 and 128 are sufficiently thin that they can be viewed as a straight cross-section.

As can be seen from Figure 4, the slope is this Cross-section compared to the Z-Z axis in contrast to the slope in a spherical segment non-uniform, d. H. the angle of attack of the Fresnel effective flanks thus formed changes over the circumference of each ellipsoidal segment 124, 126 and 128.

If the inner surfaces of ellipsoids 124, 126, and 128 are reflective, then a light source will be which is placed e.g. at the focal point 116, and its light at any point of the ellipsoidal segments 124, 126 and 128 can impinge, reflected after the focal point 188. Because of the geometric properties of an ellipsoid, such a reflection occurs without introducing comatic and astigmatic aberration errors in the image of the light source focused at point 118.

If now a large number of ellipsoids, e.g. B. the ellipsoids 110, 112 and 114 is considered, which the Intersecting planes 120 and 122, it becomes clear that a large number of concentric ellipsoidal segments 124, 126, 128 is formed, thereby causing a light source to be placed in one of the focal points is reflected towards the other focal point. If a large number of ellipsoidal segments 124, 126, 128 are used, one can be relatively flat Reflective surface are created, whereby essentially all light from a light source, which is arranged at one focal point of the ellipsoids, after the other focal point of these ellipsoids is judged. This is the principle according to which the novel setting screen 64 according to FIG. 1 constructed where one of the focal points corresponds to the pupil point 86 and the other from the apparent position of the The center point of the inlet opening 66 is defined.

Reference is made to the "apparent" location of the center point of the inlet opening 66 because the optical path 80 (Fig. 1) from adjustment screen 64 to the entrance opening 66 first after the viewfinder mirror 30 runs so that the inlet opening 66 closes opposite the setting screen 64 behind the viewfinder mirror 30 seems to lie. When the setup screen 64 is constructed in accordance with the above teachings, it follows that im essentially the entire amount of light entering through the camera 10 through the lens 14, which is passed through the Finder mirror 30 is reflected after the setting screen 64, from this screen 64 through the entrance opening 66 (via the upper part of the viewfinder mirror 30) after the viewfinder 34 is reflected.

In the following, on F ί g. 5 referred to. The in F ί g. The setting screen 64 shown in FIG. 1 is constructed here according to an embodiment of the invention. In Fig. 5 the screen is shown partially in section and aligned in the manner shown in FIG. 4 with respect to the axes XX, Y-Y and ZZ. The screen 64 according to FIG. 5 consists of a large number of concentric, staggered surfaces 130 which form the effective Fresnel flanks and which, as best shown in FIG. 7 can be seen, in the plane defined by the XX and YY axes, have an elliptical shape. As can be seen from FIG. 5, the staggered surfaces 130 change in their angle of attack over the circumference. The angle of attack changes along the XX axis compared to that of the YY axis. This change is a result of the fact that the effective flanks 130 approach segments of ellipsoids, the major and minor axes being of different lengths.

Typically, the adjustment screen 64 is made of plastics such as acrylic or vinyl based and the like Active flanks 130 are provided with a reflective coating made of aluminum. It is on it, however to point out that the surfaces 130 are not completely smooth, but by smooth bumps or others Irregularities are marked.

As a result of these bumps or the like, the light incident on any of the surfaces 130 is in randomly distributed within a predetermined fixed angle, causing the adjustment screen 64 to still all of the incident light originating from the exit pupil 84 through the entrance aperture 66 can direct, but with a certain static scattering of light. Through these increases or the like it becomes possible that the operator need only determine whether an image is in focus Screen 64 is shown in order to then make the distance adjustment of the lens 14.

The possibility of adjustment on the screen 64 is obtained as a result of the random dispersion, while the Brightness of the image is ensured by having substantially all of the image covering the screen 64 of reaches the exit pupil 84, through which the entrance opening 66 can pass to the viewfinder 34.

It has been found that a cheaper, and also more satisfactory, viewing screen 64 can be obtained by making staggered surfaces 130 which provide a first approximation of a series of ellipsoidal segments. Such a first order approximation can be effected in that a screen 64 'is generated in which the cross-sectional inclinations of the surfaces 132 with respect to the ZZ axis coincide with those of the ellipsoidal segments, as they are in the case of the surfaces 130 according to FIG. 5, but with the difference that each surface is circular in the plane defined by the axes XX and YY. Such a first order approximation can be seen from FIGS. 6 and 8 can be seen.

As shown in FIG. 6, the setting screen 64 'consists of several concentrically arranged active flanks 132. If the single-skin screen 64' according to FIG. 6 compares with the setting screen 64 according to FIG. Likewise, the cross-sectional slope of surfaces 132 along the Y-Y axis can be shown to approximate that of surfaces 130.

Reference is made to FIG. 8 below. It can be seen from this that the surfaces 132 differ markedly from the surfaces 130 according to FIG. 7, namely in that the active flanks 132 are circular in the plane defined by the axes XX and YY. Although certain inaccuracies in this embodiment according to FIG. 8 compared to the exemplary embodiment according to FIG. 7 adhere, these inaccuracies can be reduced to a minimum by arranging the active flanks 132 in such a way that their common center 134 does not coincide with the center of the screen 64 '. The position of the center 134 relative to the center of the screen 64 'is determined with reference to the exit pupil 84 and the entrance pupil, which is determined by the entrance opening 66, as when using a conventional Fresnel mirror according to FIG Axis.

Although the setting screen 64 'according to FIG. 8 seems to be similar to the known Fresnel mirror according to FIG. 3, the difference becomes clear by referring to FIG. 9 in comparison with FIG. 6. The Fresnel mirror 100 according to FIG. 9 is oriented in the same way with respect to the axes XX, YY and ZZ , ie the screen 64 'according to FIG. 6. It can be clearly seen, however, that the effective flanks 136 differ significantly in their cross-sectional inclination with respect to the Z-axis from the effective flanks 132 of the screen 64 '. This difference in the cross-sectional inclination leads to the noticeably improved brightness at the viewing station 82 of the camera 10 according to FIG. 1, if the screen 64 'according to FIG. 6 is used instead of a known Fresnel mirror, as shown in FIG. 3 and 9 is shown.

For this purpose 4 sheets of drawings

Claims (3)

Patent claims: 1. Optically effective, reflective setting screen for a reflex camera, on which the camera lens generates a real image via a viewfinder mirror, which is reflected in the viewfinder, whereby the setting screen is designed as a stepped reflector of the Fresnel design, in which the angle of attack of the concentric effective flanks are change from step to step in order to form a concave mirror which images the exit pupil of the camera lens in the viewfinder area in the form of a viewfinder pupil, characterized in that the angle of incidence of each active flank (130; 132; 140) changes within a step over the circumference in such a way that that the active flanks result in a flat approximation of an ellipsoidal reflector whose two focal points (116, 118) essentially coincide with a point of the exit pupil (84) of the camera lens (14) or a point of the viewfinder pupil (66). 2. Optically effective setting screen for a single lens reflex camera according to claim 1, characterized in that the active flanks (132; 140) are circular. 3. Optically effective setting screen for a reflex camera according to Claims 1 and 2, characterized in that the active flanks (131; 140) have a structured surface (130) in a manner known per se.