DE102014113147B4 - Procedure to avoid stray light on frame parts or lens edges - Google Patents

Abstract

Method for avoiding scattered light on frame parts or lens edges outside of the useful beam path transmitted by optical imaging systems, characterized in that the surfaces illuminated from the object side within the imaging system are designed so that they are not visible from the image side and those from the image side visible surfaces cannot be illuminated from the object side by - using the optical construction data of the optical imaging system to determine the free lens diameter necessary for image transmission, - using the free lens diameter to determine the envelope rays of all useful beams necessary for image transmission, - in cutting planes ( 7) perpendicular to the optical axis (8) of the optical imaging system, the critical angles (9) of all exit beam bundles are determined, which from the optical subsystem (10) lying in front of the cutting plane (7) in the direction of the light into the envelope Rahlen enclosed area can emerge, whereby to determine this critical angle (9), the angle of the beam entering the optical subsystem from the object space is enlarged with a ray tracing process until no more light passes through the subsystem (10) and for that In the light direction behind the cutting plane (7) lying optical subsystem (11), the critical angles (12) of all entrance beams are determined, which can pass through this subsystem (11) from the area enclosed by the enveloping rays, whereby this critical angle is determined (12) the angles of the 10 bundles of rays entering the optical subsystem (11) from the investigated area are enlarged using a ray tracing process until no more light enters the image space, - the angles of inclination for parts of the frame lying outside the envelope rays and Lens edges in the area in front of the cutting plane 15 (7) larger than the size nzwwinkel (12) of the entrance beam and - in the area behind the cutting plane (7) greater than the critical angle (9) of the exit beam.

Description

The invention relates to a method for avoiding scattered light on frame parts or lens edges of optical imaging systems.

Scattered light in optical imaging systems can arise when a surface within the optical system, e.g. the cylinder of an intermediate ring, is illuminated by an external light source through optical subsystems in front of this surface. This surface scatters the light falling on it more or less violently depending on the angle of incidence and the nature of the surface. The surface appears more or less bright in the optical system. The scattered light can be imaged directly through the underlying optical subsystem in the image field in the case of lenses or in the area of the exit pupil in the case of observation devices. If the light energy with which a surface is illuminated is very high, e.g. if the light is focused, then the scattered light can also illuminate other parts of the holder, which in turn scatter the light falling on them. This light can also enter the image field through the optical subsystem located behind it. Such multiple reflections at the frame parts can be neglected in most cases because of the lower residual energy. However, they must be taken into account in prism and mirror systems. If the area causing the scattered light is close to a pupil plane, e.g. in the lens of binoculars or in the aperture area of an objective, then a large area of the image field is overexposed. The image appears milky. If the surface is in the vicinity of an intermediate image, e.g. a telescope, then there are reflections in the image that tend to be punctiform or very small surfaces with more or less pronounced imaging errors.

A classic method for reducing such stray light effects is to matt black the critical frame parts or lens edges or to provide longer frame cylinders with concentric grooves. However, these flutes only act like a matt black surface, but do not completely prevent the scattered light because the flank angles of the individual flutes are so steep that they always have a rounding or a small cylinder together with their adjacent flank. Several of these ridges together then act like a normal surface.

Out US 8 764 204 B2 a lens mount for objectives is known in which sawtooth-shaped annular surfaces are arranged on the cylindrical inner surface between groups of lenses to suppress stray light. The tooth gaps are designed so that the inclination of the tooth flank facing the object side is greater than the maximum angle of the imaging rays entering the lens and the inclination of the tooth flank facing the image side is equal to or greater than the maximum angle of the imaging rays directed towards the image side. In the valley of the tooth gap there should be a flat area parallel to the optical axis of the objective. The inclinations of the tooth flanks are different depending on the distance to the entrance opening of the imaging beams.

Other methods, lens mounts and optical imaging systems for suppressing stray light are off DE 14 97 574 A , DD 284 568 A7 , DD 270 449 A3 , DD 275 535 A1 , DE 85 25 703 U1 and DE 42 06 357 C1 known.

For the development of imaging optical systems one used for many decades so. sequential ray tracing software (lens design programs). The rays hit the optical surfaces in a fixed, predetermined sequence.

Sequential ray tracers are very well suited for optimizing imaging systems, i.e. for iterative adaptation of the optical system data to a desired optimum of the imaging quality. The lens design programs, however, neglect the influences of the mechanical environment of the lenses, such as lens mounts, apertures, housings, on which light can be scattered. The sockets for the calculated optical system are designed in a separate development, so that the system can usually only be examined for the effects of stray light after a prototype is available.

In Laser + Photonik, 2007 (5), pages 18-22, a so-called. specified non-sequential ray tracing program, which should model the light propagation within the optical system in a physically correct manner and should therefore be suitable for simulating virtual prototypes. The beam path through the system is not assumed to be fixed from the start. The ray tracer constantly recalculates which physical object a ray will hit next. All mechanical parts, such as lens mounts and diaphragms, which are imported from a CAD program in most cases, are referred to as physical objects. However, it is also possible to use script to design realistic lens mounts, a simplified housing and lens rims for a virtual prototype in essential details.

A non-sequential ray tracer should take into account both reflection from surfaces and diffuse scattering. The number of resulting rays in the system increases considerably in this way, so that suitable Termination criteria must ensure that the computing time for the simulation can be completed in a reasonable and, above all, sensible time frame.

The invention was based on the object of providing instructions for the frame construction for which specific construction parameters can be determined in a targeted manner in order to avoid stray light using conventional sequential ray tracing software.

This object is achieved in a method according to the invention in that the areas illuminated from the object side within the imaging system are designed so that they are not visible from the image side and the areas visible from the image side are not visible from the object side can be illuminated by performing the method steps specified in claim 1. Advantageous refinements of this instruction result from the features of the subclaims.

This instruction is based on the knowledge that an area within the optical system can only cause direct scattered light if it is visible both from the object side and from the image side. This applies, for example, to cylindrical surfaces that are parallel to the optical axis if they are close to the space required for the transmission of useful light. For the frame designer there is therefore the teaching of arranging such surfaces as far as possible outside the useful light beam, taking into account mechanical requirements.

Whether an area within the optical system can be illuminated from the object side depends on the critical angle of a beam that can exit the optical subsystem in front of this area and reach this area. To determine this critical angle, the angles of the bundles of rays entering the optical subsystem from the object space are enlarged with the ray tracing software until no more light passes through the subsystem.

Whether an area within the optical system is visible from the image side depends on the critical angle of a beam that can enter the optical subsystem behind this area from this area and exit from this subsystem on the image side. To determine this critical angle, the angles of the bundles of rays entering the optical subsystem from the examined surface are enlarged with the ray tracing software until no more light enters the image space.

Since the ray tracing programs are designed for beam guidance from the object side to the image side, the determination of the first-mentioned critical angle can be simplified by reversing the sequence of the lenses of the subsystem.

If a surface that is illuminated from the object space has a greater angle of inclination with respect to the optical axis than the critical angle of the entrance beam for the subsequent optical subsystem, then this surface is not visible from the image side.

If a surface that is visible from the image side has a greater angle of inclination with respect to the optical axis than the critical angle of the exit beam of the preceding optical subsystem, then this surface cannot be illuminated from the object side.

As long as the surface areas mentioned lie outside the critical angles determined by the method according to the invention, they are not illuminated from the object side and are not visible from the image side. The shape of such surfaces can be designed freely.

In addition to the usual design parameters, such as free lens diameter, lens thickness and lens spacing, the frame designer can therefore also specify the angles of inclination for selected cutting planes between the lens elements. If it emerges from the frame construction that, due to mechanical stability conditions, the specified angles of inclination can only be maintained over a limited extent along the optical axis, the angle of inclination can be simply redefined in further cutting planes.

The usual design rule, according to which all mechanical mount parts are to be arranged as far apart from the imaging beam path as possible, can be optimized with regard to the necessary spacings if the required angle of inclination is observed, so that the weight and size of the mount can be minimized.

The method can also be used with advantage on the basis of a first draft of a frame construction to check and optimize the angles of inclination on frame parts and within longer glass paths, such as in prism systems.

• 1 einen Linsenschnitt für ein Objektiv zur Darstellung der freien Linsendurchmesser und Hüllstrahlen,
• 2 ein Teilsystem daraus mit Grenzwinkel der Austrittsstrah lenbündel,
• 3 ein nachfolgendes Teilsystem mit Grenzwinkel der Eintrittsstrahlen und
• 4 einen Fassungsteil mit unterschiedlichen Neigungswinkeln.

In the drawing, an exemplary embodiment to clarify the process steps is shown schematically and is explained in more detail below with reference to the figures. Show it

• 1 a lens section for a lens to show the free lens diameter and envelope rays,
• 2 a subsystem from it with the critical angle of the exit beam bundle,
• 3 a subsequent subsystem with critical angle of the entrance rays and
• 4th a socket part with different angles of inclination.

1 shows a lens section determined on the basis of optical construction data through an objective. The one in one picture plane 1 generated pixels 2 by an edge ray bundle 3 determine the necessary free lens diameter. The light entry side limitation 4th Marginal ray bundle 3 together with the marginal rays running within the lens incision 5 for a central pixel 6th result when rotating around the optical axis 8th the envelope rays for the useful rays used for image generation.

2 shows in a sectional plane 7th perpendicular to the optical axis 8th of the imaging system the critical angle 9 of the exit beam that emerges in the light direction in front of a cutting plane 7th lying first optical subsystem 10 can exit into the area enclosed by the envelope rays.

3 shows for that in the direction of light behind the cutting plane 7th second optical subsystem 11 the critical angle 12 of the entrance beam emerging from the area enclosed by the envelope beams through the second optical subsystem 11 can get through.

4th shows schematically a cutting plane lying between optical subsystems 7th and an associated frame geometry outside of the envelope rays. The angle of inclination in the direction of light in front of the cutting plane 7th lying frame area is larger than an associated limit angle 12 the entrance beam. The angle of inclination of the behind the cutting plane 7th adjacent frame area is larger than an associated critical angle 9 the exit beam.

The investigation according to the invention of a further cutting plane, e.g. in the area of the subsequent long rising flank, may also require an individual design with different angles of inclination in this area.

In the same way, frame parts for and lens edges on lens elements of the in 1 to design lens shown, which lie outside the envelope rays.

List of reference symbols

1

Image plane

2

Pixel at the edge

3

Marginal ray bundle

4th

Limitation of the marginal ray bundle

5

Edge rays for the central pixel

6th

central pixel

7th

Cutting plane

8th

optical axis

9

Critical angle exit ray bundle

10

first optical subsystem

11

second optical subsystem

12

Critical angle of the entrance beam

Claims (6)

Method for avoiding scattered light on frame parts or lens edges outside of the useful beam path transmitted by optical imaging systems, characterized in that the surfaces illuminated from the object side within the imaging system are designed so that they are not visible from the image side and those from the image side visible surfaces cannot be illuminated from the object side by - using the optical construction data of the optical imaging system to determine the free lens diameter necessary for image transmission, - using the free lens diameter to determine the envelope rays of all useful rays necessary for image transmission, - in cutting planes ( 7) perpendicular to the optical axis (8) of the optical imaging system, the critical angles (9) of all exit beam bundles are determined, which from the optical subsystem (10) lying in front of the cutting plane (7) in the direction of the hips llbeams can exit the area enclosed, whereby to determine this critical angle (9) the angle of the bundle of rays entering the optical subsystem from the object space with a ray tracing The process is enlarged until no more light passes through the subsystem (10) and - for the optical subsystem (11) located behind the cutting plane (7) in the direction of light, the critical angles (12) of all the entrance beams are determined, which are from the area enclosed by the enveloping rays can pass through this subsystem (11), whereby to determine this critical angle (12) the angles of the 10 bundles of rays entering the optical subsystem (11) from the examined surface are enlarged with a ray tracing method , until no more light enters the image space, - the angle of inclination for frame parts and lens edges lying outside the envelope rays in the area in front of the cutting plane 15 (7) is greater than the critical angle (12) of the entrance beam and - in the area behind the cutting plane ( 7) greater than the critical angle (9) of the exit beam can be selected. Procedure according to Claim 1 , characterized in that a frame construction is created taking into account the enveloping rays and, in selected cutting planes through the frame construction, the angle of inclination of the frame parts and lens edges are checked for compliance with the angle of inclination necessary to avoid stray light and, if necessary, optimized. Procedure according to Claim 1 , characterized in that, taking into account the enveloping rays, a frame construction is created and a check is made to determine whether all frame parts and lens edges are outside the angle of inclination necessary to avoid stray light and, if necessary, individual frame parts or lens edges are optimized accordingly. Procedure according to Claim 2 or 3 , characterized in that depending on the angles of inclination and mechanically necessary frame construction elements, the checking and optimization is carried out iteratively in cutting planes lying one behind the other. Procedure according to Claim 1 , characterized in that the edges of the surfaces of the mount parts and lens edges adjoining the envelope rays are formed with sharp edges. Procedure according to Claim 1 , characterized in that 15 adjacent surface elements running parallel to the optical axis, which are both illuminated from the object side and visible from the image side, are provided with a sawtooth contour whose angle of inclination corresponds to the conditions necessary to avoid stray light .

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