DE29724381U1 - Data exposure unit for a camera - Google Patents

Description

Data recording unit for a camera

The invention relates to a data exposure unit used in a camera to expose data such as date and/or time onto a film.

A known data exposure unit contains a light-emitting unit and an optical imaging system. The light-emitting unit contains several light-emitting diodes (LEDs) that are aligned along a straight line perpendicular to the film travel direction. The optical imaging system generates light points on the film in accordance with the light-emitting diodes. The light-emitting diodes are controlled synchronously with the film transport in order to expose data, such as the date, as an image with pixels arranged in a matrix.

In the known data exposure unit, the LEDs are arranged independently of each other on a circuit board, and thus the distance between adjacent LEDs must be relatively small due to the size of the LEDs.

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large. For example, the distance between light-emitting elements of adjacent LEDs is generally more than 0.5 mm. If the data recording unit has seven LEDs, the distance between the outer light-emitting elements is at least 3.3 mm.

However, the size of the characters (letters) of the printed data should be limited to a range of about 0.4 to 0.7 mm in a direction perpendicular to the film running direction so that the exposed data does not overlap with the image of a developed photograph. Thus, the imaging optical system of the known unit is a reducing optical system in which an imaging magnification is in the range of about 0.1 to 0.2.

One problem is that the exposure position on the film may vary depending on errors in the optical imaging system, such as a positioning or manufacturing error. Furthermore, the displacement of the exposure position due to a given error increases as the imaging scale becomes smaller. Thus, the error tolerance of the conventional data exposure unit is small. Therefore, the optical imaging system of a conventional data exposure unit must be manufactured and positioned with great precision to guarantee a constant printing position; however, the measurements required for this increase the cost of assembly and manufacturing.

Since many parts of the camera are now made of plastic, errors in the positioning of the optical imaging system are mainly caused by molding errors generated by temperature changes of the plastic parts during molding and forming.

It is the object of the invention to provide a data exposure unit for a camera in which the error tolerance in the optical imaging system is relatively large, i.e. that the

Shift of the exposure position due to errors is small.

This object is achieved by a data exposure unit having the features of claim 1. Advantageous embodiments are specified in the subclaims.

In order to achieve the object of the invention, the data exposure unit includes a light-emitting unit with a plurality of light-emitting elements and an optical imaging system for generating light spots on the film corresponding to the light-emitting elements. The optical imaging system satisfies the following condition:

where m is the magnification of the optical imaging system

In one embodiment of the data exposure unit according to the invention, the light-emitting elements are aligned on a straight line that runs perpendicular to the film travel direction.

In a further embodiment of the data recording unit according to the invention, the light emitting unit includes a light emitting diode having a plurality of light emitting elements on a single substrate.

The optical imaging system in the data exposure unit according to the invention has a single imaging lens or several lenses. If the optical imaging system contains only a single lens, this is constructed in one embodiment in such a way that light incident on the imaging lens is not reflected at all or is only reflected in the edge areas of the imaging lens. Advantageously, at least

At least one of the lens surfaces of the imaging lens has an aspherical surface.

If the optical imaging system contains a first and a second imaging lens, in a further embodiment an entrance surface and an exit surface of the first imaging lens are offset from one another in the film running direction or against the film running direction. In this case, the first imaging lens has two reflective surfaces on the edge surfaces between the entrance surface and the exit surface. Furthermore, an entrance surface and an exit surface of the second imaging lens can be offset from one another in the film running direction or against the film running direction. In this case, the second imaging lens also has two reflective surfaces on the edge surfaces between the entrance surface and the exit surface.

If the first and second imaging lenses each have two reflective surfaces, the entrance surface of the first imaging lens and the exit surface of the second imaging lens are advantageously aligned with respect to the film travel direction and the exit surface of the first imaging lens and the entrance surface of the second imaging lens are aligned with respect to each other with respect to the film travel direction.

In the following, embodiments of the invention are explained with reference to the drawings.

Figure 1 is a sectional view of a camera with a data exposure unit,

Figure 2 is a schematic view of the arrangement of the light-emitting elements on a light-emitting unit,

Figure 3 shows an optical imaging system according to a first embodiment,

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Figure 4 shows an optical imaging system according to a second embodiment, and

Figure 5 shows an optical imaging system according to a third embodiment.

Figure 1 shows the structure of a compact camera. For the following description, the front side F is defined as the side facing an object (right side in Figure 1) and the back side R is defined as the side facing away from the front side F (left side in Figure 1).

The camera has a camera housing 10 and a camera back 15 which is rotatable about a rotation axis 15a to close an opening on the back R of the camera housing 10.

The camera body 10 contains a lens compartment 11 (shown as a rectangular area in Figure 1) in which a zoom lens barrel (not shown) is arranged, a film chamber 12 in which a film cartridge is mounted, and a winding chamber 14. In the winding chamber 14, a film take-up spool 13 is arranged for winding the film (not shown) drawn out from the film cartridge. The film chamber 12 and the winding chamber 14 are arranged on the sides of the lens compartment 11 so that the film is moved in a film running direction D which is perpendicular to the direction from the front side F to the rear side R of the camera. Furthermore, a diaphragm (not shown) is arranged on the side of the lens compartment 11 facing the rear side R to define an exposure area of the film.

A pressure plate 16 is held on the inside of the camera back 15 by a leaf spring (not shown). A pair of film guide rails 17a, which extend from the film chamber 12 to the spool chamber 14, are formed on a chassis 17 in the area blocked by the diaphragm, and the pressure plate 16 is

pressure plate 16 (i.e. on the side of the lens compartment 11 facing the rear side R). The film is pressed against the film guide rails 17a by the pressure plate. After an image portion of the film located on the side of the aperture facing the rear side R is exposed, the film runs in the film running direction D as the film take-up spool 13 rotates.

A data recording unit 20 is arranged between the lens room 11 and the winding chamber 14. The data recording unit 20 includes a light emitting unit 21 fixed to the front of the chassis 17 and an imaging lens 22 as an imaging optical system. The light emitting unit 21 includes a light emitting diode 21a. The light emitting diode 21a includes a plurality of light emitting elements on a single substrate and a cover glass 21b covering the light emitting surface of the light emitting diode 21a.

The light from each light emitting element 21c is imaged by the imaging lens 22 onto the film to form light spots on the film surface corresponding to the light emitting elements 21c. The light emitting diode 21a in this example includes seven light emitting elements 21c, as shown in Figure 2. The light emitting elements 21c are aligned on a straight line, and the direction of the straight line is the same as that of the corresponding light spots on the film. The straight lines are perpendicular to the film running direction D, i.e. perpendicular to the sheet in Figure 1.

The light emitting unit 21 is controlled so that each of the light emitting elements 21c emits light in synchronism with the film running movement to print character data as pixels arranged in a matrix on the film.

The printing position P is located between the aperture and the winding chamber 14 at a point where a viewed image section passes after it has been at the exposure position

(photographing position) in the direction of film travel. The data, e.g. the date, is recorded on the already exposed image section after exposure (photographing), while the film continues to run after the shutter is released.

The position of the data recording unit 20 of the embodiment is based on the assumption that the film is drawn out of the film cartridge after exposure of each frame. However, the data recording unit 20 of the embodiment is also used in a "preload" camera in which the film is wound onto a film take-up spool after it is loaded and the film is then drawn into the film cartridge after exposure of each frame. In such a "preload" camera, the data recording unit 20 is arranged between the lens compartment 11 and the film chamber 12. In this specification, the term "film travel" means the movement of the film by one frame after each exposure (photo capture).

When the imaging optical system consists of a single imaging lens 22 without reflective lens surfaces, both the light emitting unit 21 and the printing position P are located on the optical axis of the imaging lens 22, as shown in Figure 1.

For the magnification m of the optical imaging system

An upright image is formed on the film when m has a positive value (m > 0); an upside down image is formed when m has a negative value (m < 0). If the absolute value of the magnification IτηI is less than 0.6, the distance between adjacent light-emitting elements (i.e., an element offset)

is too large for a given character size (similar to the problem in the well-known data exposure unit). Therefore, the camera cannot be made compact, and the error tolerance for the positioning error of the imaging optical system becomes smaller. On the other hand, when the absolute value of the imaging magnification ImI is larger than 1.5, the required manufacturing accuracy of the imaging optical system becomes higher because the distance between the adjacent light-emitting elements is too small and thus high resolution is required for the imaging optical system.

In the embodiment, the distance between the adjacent light-emitting elements 21c is 0.09 mm, and the distance between the outer light-emitting elements is 0.6 mm, as shown in Figure 2. As already explained, the size of the characters (letters) of the exposed data is limited to a range of approximately 0.4 to 0.7 mm in the direction perpendicular to the film running direction D, thus limiting the magnification of the imaging optical system to a range of approximately 0.67 < |m| < 1.17 when the light-emitting diode 21a is used. That is, the imaging optical system produces an approximately scaled image of the lined-up light-emitting elements 21c on the film. Thus, a shift in the exposure position due to a manufacturing error or assembly error of the imaging lens 22 is reduced compared to the known unit which has an imaging magnification of 0.1 or 0.2.

Three embodiments are explained below, which are numerical examples of the optical imaging system used in the data exposure unit. Figures 3 to 5 show the structure of the optical imaging system as a first, second and third embodiment. The drawings show a film 18 on which an image is to be produced.

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In the first embodiment, the imaging optical system includes the single imaging lens 22 as shown in Figs. 1 and 3. The imaging lens 22 has an entrance surface 22a through which the light from the light emitting unit 21 enters and an exit surface 22b through which the light exits toward the film 18. The light is not reflected in the imaging lens 22.

The optical imaging system of the second embodiment shown in Figure 4 contains a single imaging lens 23, the entrance surface 23a and exit surface 23b of which are offset from one another against the film running direction D. Alternatively, and depending on the design of the camera, the exit surface 23b can also be offset in the film running direction D. In the second embodiment, light from the light-emitting unit 21 enters the entrance surface 23a of the imaging lens 23 and is reflected twice at total reflection surfaces 23c and 23d. The reflected light then exits through the exit surface 23b to the film 18.

The optical imaging system of the third embodiment shown in Figure 5 includes a first imaging lens 24 and a second imaging lens 25 which are constructed similarly to the imaging lens 23 of the second embodiment. The first imaging lens 24 includes two total reflection surfaces 24c and 24d between the entrance surface 24a and the exit surface 24b to offset the light path in a direction opposite to the film running direction D. The second imaging lens 25 includes two total reflection surfaces 25c and 25d between the entrance surface 25a and the exit surface 25b to offset the light path in the film running direction D. In an alternative arrangement, the first imaging lens 24 is arranged so that it offsets the light path in the film running direction D. The second imaging lens is arranged in the alternative arrangement so that it

away in the direction opposite to the film running direction D.

In the third embodiment, the exit surface 24b of the first imaging lens 24 and the entrance surface 25a of the second imaging lens 25 are aligned with each other with respect to the film running direction D.

In the second and third embodiments, the exposure position can be set more freely without being tied to the position of the light-emitting unit 21. The arrangement of the third embodiment is used in particular when the free space between the lens chamber 11 and the winding chamber 14 is smaller than in the arrangement of Figure 1.

The numerical values for the first, second and third embodiments are given below in Tables 1, 2 and 3.

In the tables, r denotes the radius of curvature of a surface (the value at the vertex for an aspherical surface), d a distance between surfaces along the optical axis, nd the refractive index at a wavelength of 588 nm and vd the Abbe number.

In the tables, the surface number 1 represents the light-emitting surface of the light-emitting unit 21. The surface number 2 represents the side of the cover glass 21b facing the rear side R, so that the distance between the surface with the surface number 1 and the surface with the surface number 2 indicates the thickness of the cover glass 21b. In Tables 1 and 2, the surface number 3 represents the entrance surface 22a or 23a of the imaging lens 22 or 23. The surface number 4 represents the exit surface 22b or 23b of the imaging lens 22 or 23. The surface number 5 represents the film 18. In Table 3, the surface numbers 3 or 4 represent the

Entrance surface 24a and exit surface 24b of the first imaging lens 24; the surface numbers 5 and 6 respectively designate the entrance surface 25a and exit surface 25b of the second imaging lens 25, and the surface number 7 stands for the film 18.

The optical imaging system of each embodiment includes at least one aspherical surface in order to achieve sufficient imaging performance (e.g. low aberration) even when only a few lenses are used. The exit surface 22b of the imaging lens 22 in the first embodiment (fourth surface in Table 1), the entrance surface 23a and the exit surface 23b of the imaging lens 23 in the second embodiment (third and fourth surfaces in Table 2) and the exit surface 24b of the first imaging lens 24 in the third embodiment (fourth surface in Table 3) are rotationally symmetrical aspherical surfaces.

An aspherical surface is represented by the following equation:

^CY2

(K+l)Y ² C ²

where X is the distance of a curve from a plane at a point where the height from the optical axis is Y. The plane is located at the optical axis tangent to the curve. C is the curvature (l/r) at the vertex of the surface, K is a conic constant, and A4 is a fourth-order aspherical area coefficient. The constant K and the area coefficient A4 are given below each table.

8th, r 0 Table 1 1 nd vd m = -0.75 -3 OO 9 ,49176 57.4 Area number 00 5 d 1 1 673 8th .62 ,49176 57.4 2 ,208 ,64 3 00 ,00 4 ,63 5

Aspherical data for the fourth surface: K=-l A ₄ =2.76-10~ ³

4, r 0 Table 1 2 nd vd m = -1.00 -4 00 8th ,49176 57.4 Area number 00 6 d 1 1 500 9 .62 ,49176 57.4 2 ,500 ,74 3 00 ,50 4 ,15 5

Aspherical data for the third surface Aspherical data for the fourth surface:

K=-2.23 A ₄ =OK=-2.23 A ₄ =O

4, r Table 1 3 nd Vd m = -1.15 -5 00 ,49176 57.4 Area number 4, OO d 1 - ^: 1". 799 0.62 ,49176 57.4 2 ,469 4.87 1 3 865 6.80 ,49176 57.4 4 00 3.92 5 OO 6.80 6 3.00 7

Aspherical data for the fourth surface: K=-l A ₄ =I, 90-10" ³

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In each embodiment, the image formed on the film 18 is an inverted image because the magnification m has a negative value (m < 0). However, an upright image can also be formed by using an image inversion element in the optical imaging system. To increase the error tolerance of the optical imaging system, only the absolute value of the magnification needs to be considered, and the sign (plus or minus) of the magnification can be optionally set.

Since the magnification of the optical imaging system in the present invention is in a range between 0.6 and 1.5, the misalignment of the light spots on the film due to manufacturing and positioning errors of the optical imaging system can be reduced compared to the known data exposure unit. Thus, the error tolerance for a manufacturing error in a lens, a manufacturing error in a reflecting surface or a positioning error of an element is larger when the required positioning accuracy for the light spots on the film is the same as that of conventional devices. If the elements are manufactured and assembled with the same accuracy as for a conventional device, the light elements can thus be positioned more accurately on the film.

Claims (13)

1. Data exposure unit ( 20 ) for a camera ( 10 ) for exposing data patterns on a film ( 18 ) synchronously with the transport movement (D) of the film ( 18 ), with a light-emitting unit ( 21 ) which contains a plurality of light-emitting elements ( 21 c), and with an optical imaging system ( 22 ) for generating light points on the film ( 18 ) corresponding to the light-emitting elements ( 21 c), characterized in that the optical imaging system ( 22 ) satisfies the following condition:

0.6 < |m| < 1.5,

where m is the imaging scale of the optical imaging system ( 22 ). 2. Data exposure unit ( 20 ) according to claim 1, characterized in that the light-emitting elements ( 21 c) are aligned along a straight line. 3. Data exposure unit ( 20 ) according to one of the preceding claims, characterized in that the light-emitting unit ( 21 ) contains a light-emitting diode ( 21a ) in which the light-emitting elements ( 21c ) are arranged on a single substrate. 4. Data exposure unit ( 20 ) according to one of the preceding claims, characterized in that the light spots are arranged along a straight line perpendicular to the film running direction (D). 5. Data exposure unit ( 20 ) according to one of the preceding claims, characterized in that the optical imaging system ( 22 ) contains a single lens, through whose entrance surface ( 22a ) the light from the light-emitting unit ( 21 ) enters and through whose exit surface ( 22b ) the light exits in the direction of the film ( 18 ). 6. Data exposure unit ( 20 ) according to claim 5, characterized in that the light entering the imaging lens ( 22 ) exits without being reflected in the imaging lens ( 22 ). 7. Data exposure unit ( 20 ) according to claim 5, characterized in that the entrance surface ( 23 a) and the exit surface ( 23 b) are offset from one another in the film running direction (D) or against the film running direction (D), and that the imaging lens ( 23 ) contains two reflecting surfaces ( 23 c, 23 d) on edge surfaces between the entrance surface ( 23 a) and the exit surface ( 23 b). 8. Data exposure unit ( 20 ) according to one of claims 1 to 4, characterized in that the optical imaging system ( 24 , 25 ) contains a first and a second imaging lens ( 24 , 25 ). 9. Data exposure unit ( 20 ) according to claim 8, characterized in that an entrance surface ( 24a ) and an exit surface ( 24b ) of the first imaging lens ( 24 ) are offset from one another in the film running direction (D) or against the film running direction (D), and that the first imaging lens ( 24 ) contains two reflecting surfaces ( 24c , 24d ) on the edge surfaces between the entrance surface ( 24a ) and the exit surface ( 24b ). 10. Data exposure unit ( 20 ) according to claim 9, characterized in that an entrance surface ( 25 a) and an exit surface ( 25 b) of the second imaging lens ( 25 ) are offset from one another in the film running direction (D) or against the film running direction (D), and that the second imaging lens ( 25 ) contains two reflecting surfaces ( 25 c, 25 d) on the edge surfaces between the entrance surface ( 25 a) and the exit surface ( 25 b). 11. Data exposure unit ( 20 ) according to claim 10, characterized in that the entrance surface ( 24a ) of the first imaging lens ( 24 ) and the exit surface ( 25b ) of the second imaging lens ( 25 ) are aligned with each other in the film travel direction (D), and that the exit surface ( 24b ) of the first imaging lens ( 24 ) and the entrance surface ( 25a ) of the second imaging lens ( 25 ) are aligned with each other in the film travel direction (D). 12. Data exposure unit ( 20 ) according to one of the preceding claims, characterized in that at least one imaging lens ( 23 ) has at least one aspherical surface ( 23a ). 13. Data exposure unit ( 20 ) according to one of the preceding claims, characterized in that the optical imaging system ( 22 ) produces the light spots as an approximately scaled image of the light-emitting elements ( 21c ) on the film ( 18 ).