DE3819828A1 - Beam-splitting for optoelectronic image recording - Google Patents

Abstract

The invention relates to a device for optoelectronic image recording, preferably with line sensors according to the so-called "push-broom" method. For high geometric resolution, line sensors having a sufficiently high number of discreet individual detectors are required. Under specific circumstances, e.g. for infrared exposures, line sensors are, however, only available with a limited number of individual detectors. The invention presently described shows one way how, by the arrangement of a plurality of reflection surfaces in the focal plane of only one optical main system, the image can be divided into a plurality of partial images and these can be fed without significant beam losses, via corresponding relay optics, to corresponding line sensors of a limited number of detectors and can be scanned. <IMAGE>

Description

The invention relates to a device for the opto-electronic imaging preferably with linear line sensors according to the so-called "push-broom" - scan the object line by line or "Whisk-broom" method.. The line sensors often consist of individual detectors, which are arranged in a row.

There is a need for high geometric resolutions a correspondingly large number of discrete detector elements. For various reasons that are not to be discussed further here However, there are no sensors for certain tasks sufficiently large number of detectors available. This problem can be solved in various ways according to the prior art.

One way is in the beam path of the shot Arrange objective semi-transparent beam splitter and in to arrange several detectors in the resulting image planes, who scan the picture (see O. Hofmann: digital recording technology, image measurement and aerial photography 50 (1982) Issue 1, Pp. 22, 23). The disadvantage of this solution is that at least 50% of the radiation power through the beam splitter get lost.

A second option is to have two or more lenses to be used with parallel optical axes in their Image planes generate identical images that are created with several sen sensors can be scanned (see German patent specification No. DE 27 29 291 C2, photoelectric image converter).

The radiation loss occurring in the first example is avoided here. But the second lens creates additional effort, larger device dimensions and higher weight, which is particularly disadvantageous in the case of complex and large optical systems.

Therefore, there is a need with only one main optical system and with little or no radiation loss through use several sensors with a limited number of detectors grope, the basic requirement being that this happens without gaps and without overlap.

According to the invention, this object is achieved in that Image plane of the optical recording system or in the immediate close proximity of this image plane two or more reflections are arranged surfaces that ent in this image plane divides the still image into partial images and assigned accordingly ordered relay optics generated corresponding drawing files that be sensed by appropriate sensors.

For the technical implementation of this basic idea, it is necessary that the reflection surfaces are arranged and designed so that they can be produced technically and that a clean separation of the partial beam paths takes place without mutual interference and no or only slight radiation losses arise through pupil clipping. This solution works only strictly and without pupil cropping if the image is scanned line-by-line according to the "push-broom" or "whisk-broom" methods and consequently only one image line is to be scanned in the image plane. The greater the extent of the image to be scanned across this line, the more the rays forming the image are clipped by the adjacent reflection surfaces, which results in a corresponding loss of radiation or light in the peripheral zones of the partial images, but this may be due to radiometric calibration - and corrective measures can be compensated.

Fig. 1 to 3 explain the functional principles. Fig. 1 shows a system with two sections of a system with line-shaped scanning according to the push-broom principle in plan, elevation and side elevation, with the mirrors normal of the reflecting surfaces always perpendicular to the sensor lines shown in the reflecting surfaces.

Fig. 2 shows a three-part beam splitter in a variant of the system shown in Fig. 1.

Fig. 3 also shows a system with two sections with line-shaped scanning according to the push-broom principle, with the mirror normals of the reflecting surfaces with the sensor lines or their images depicted in the image plane of the taking lens lying in one plane.

In Fig. 1, the main optical system ( 1 ) produces an image in the main image plane or in the focal point ( 6 ), which is reflected on two reflection surfaces ( 5 ) and ( 7 ). These reflection surfaces intersect at a certain angle (in the present example in FIG. 1, this angle is 90 °), the mirror normals of the reflection surfaces lying in one plane. The straight line formed by the intersection of the reflection surfaces and lying in the reflection surfaces contains the focal point ( 6 ) and is perpendicular to the optical axis of the main optical system ( 1 ).

The partial images divided by the two reflection surfaces are each imaged via the two relay lenses ( 4 ) and ( 8 ) in their image planes ( 3 ) and ( 9 ), where they are scanned by sensors ( 3 ) and ( 9 ) will. The corresponding sensor carriers ( 2 ) or ( 10 ) can be, for example, heat sinks (dewars) for cooling infrared detectors.

These sensors ( 3 ) or ( 9 ) can consist, for example, of linear line sensors, each of which contains a certain number of individual detectors which scan the pixels depicted in this sensor line. The line sensors ( 3 ) and ( 9 ) are each aligned and focused so that their images via the relay optics in the reflection surfaces ( 5 ) or ( 7 ) images ( 11 ) or ( 12 ) with the through the intersection or Focal point ( 6 ) intersecting line of the reflection surfaces coincide and thus the overall image line in its individual sections can be scanned by the assigned sensors.

In Fig. 1, the reflection surfaces ( 5 ) and ( 7 ) of the beam splitter are shown as mirrored prism surfaces.

This formation of the beam splitter can possibly lead to that impurities on the in the main image plane Reflective surfaces lead to image disturbances.

To avoid this disadvantage, the beam splitter can be designed as shown in Fig. 2. The prism surfaces ( 14 ) and ( 16 ) of the prisms ( 19 ) and ( 23 ) are covered there by prisms ( 22 ) and ( 21 ) and supplemented into cubes. By lining up several such reflection cubes, the main image line can be extended and broken down into partial image sections as the image angle of the optical system ( 1 ) allows.

In Fig. 2 3 such cubes are put together, the middle cube ( 20 ) has no reflective surface and allows the direct, unreflected beam passage for the middle image section, the image of which lies behind the beam in the direction ( 17 ) (not shown) Sensor) is scanned.

This beam splitter, into which the rays from the main optical system are incident from direction ( 13 ), divides the image line into 3 partial images, the reflection surfaces ( 14 ) and ( 16 ) assigning the rays in directions ( 18 ) and ( 15 ) distract appropriate sensors.

The individual neighboring parts and cubes of the rays leaders have to stick to each other by putty or wringing be joined that an unimpeded flow of rays over the Dividing surfaces is possible. It becomes a pupil cut avoided.

The width b of the two outer prism cubes must be correspondingly larger in order to avoid this pupil trimming.

Fig. 3 shows a further embodiment of the beam splitter. In this case, a beam splitter prism ( 25 ) is arranged so that its roof edge is at the focal point ( 6 ) of the main optical system ( 1 ) and perpendicular to its optical axis. This roof edge divides the image into two sections ( 11 ) and ( 12 ) and the reflection surfaces ( 24 ) and ( 26 ) reflect these two partial images, each from the relay optics ( 4 ) and ( 8 ) on the line sensors ( 3 ) and ( 9 ) are mapped and scanned by them. These line sensors are aligned and focused so that their respective image is perpendicular to the roof edge of the beam splitter prism ( 25 ) and coincides with the focus point ( 6 ) or the roof edge.

While the first solution shown in Figs. 1 and 2 allows the main image line to be divided into more than two sections, the solution shown in Fig. 3 allows the division into only two sections. However, this solution has the advantage that the partial images ( 11 ) and ( 12 ) do not lie on the reflecting surfaces ( 24 ) and ( 26 ) and since there can be no image disturbances due to contamination.

Even with the solution shown in Fig. 3, it is possible to omit one of the two reflection surfaces ( 24 ) or ( 26 ) and to image the corresponding partial image with the continuous unreflected beams on the line sensor via the relay optics that are now to be arranged behind the beam splitter prism. In order to avoid pupil clipping, it is advisable, as shown in Fig. 2, to guide both the reflected and the rays that are just passing through prism cubes.

The solutions of the division of the main described here image in drawing files gives another advantage. In the The rule for such scanning systems are large opening ver ratios desired, even for large object distances, e.g. for military reconnaissance with infrared Detectors, a sufficiently large signal / noise ratio to attain a relationship.

The enlargement of the aperture with the same focal length of the main system ( 1 ) and unchanged, usually predetermined detector size may lead to unacceptable large imaging errors in the main image plane. To avoid this problem, you can with a constant opening ratio

increase the absolute values of the original aperture D to D ' and the original focal length F of the main system ( 1 ) to F' proportionally and this enlargement by a corresponding reduction in the magnification β of the relay optics back to the original value

F = β F ′

to reduce. While maintaining the enlarged opening D ', the overall system thus receives the enlarged opening ratio

while maintaining the specified focal length F and detector size.

These image sharing solutions described above have the following advantages:

• a. With a single main optical system, insofar as its angle of view permits, its image in divide several sections and from ent speaking sensor assigned to each section scan the limited number of detectors.
• b. The image or beam splitting takes place without or only with relatively little radiation loss.
• c. The sensors for scanning the partial images can be in outer dimensions can be practically any size without hindering each other. It is special important when scanning with infrared detectors that for cooling in a cooling device (Dewar) are bedded.

Claims (6)

1. Device for opto-electronic image recording by scanning, preferably with line sensors according to the so-called push-broom principle, characterized in that

• - That an optical main system generates an image, which is divided by two or more reflection surfaces arranged in or in the immediate vicinity of the image plane and generates corresponding partial images via correspondingly assigned relay optics, which are scanned by appropriate sensors.

2. Device according to claim 1, characterized in

• - That the reflection surfaces intersect at a certain, preferably right angle, the mirrors are normal in one plane and the straight line formed by the intersection and lying in the reflection surfaces contains the focal point ( 6 ) of the main optical system ( 1 ) and perpendicular to it optical axis stands and
• - That the image scanning of the partial images is carried out with a preferably line-shaped sensor according to the push-broom principle, which is oriented such that the image of the sensor line generated via the relay optics coincides with the intersection line of intersection of the reflection surfaces and the corresponding line section is scanned .

3. Device according to claims 1 and 2 characterized thereby records that the reflection forming the beam splitter surfaces each formed by mirrored diagonal surfaces and the individual neighboring prism cubes optical putty or wring are joined together so that the passage of rays from one to the other prism cube without significant loss of radiation. 4. Device according to claims 1, 2 and 3 characterized thereby records that a prism cube has no reflective surface and the corresponding section in the direct beam passage is mapped onto a corresponding sensor without reflection. 5. The device according to claim 1, characterized in that a Beam splitter prism is arranged so that its roof edge at the focal point of the main optical system and at right angles to its optical axis and that the line sensors are arranged and focused so that their respective image is perpendicular to the roof edge of the beam splitter prism and their drawing files in one plane with the roof edge of the Main image plane containing beam splitter prism. 6. The device according to claim 1, characterized in that by reducing the magnification β of the relay optics with a simultaneous proportional increase in the focal length from F to F ' and the opening from D to D' of the main optical system, the opening ratio of the overall system can be enlarged, the total focal length F and thus the detector size keeping the original, predetermined value.