GB2122385A

GB2122385A - Brightness-control apparatus for a system for reflecting images into a microscope

Info

Publication number: GB2122385A
Application number: GB08315354A
Authority: GB
Inventors: Dr Georg Nyman; Peter Rojatz
Original assignee: C Reichert Optische Werke AG
Current assignee: C Reichert Optische Werke AG
Priority date: 1982-06-18
Filing date: 1983-06-03
Publication date: 1984-01-11
Also published as: GB8315354D0; GB2122385B; FR2528988A1; JPS595219A; DE3222915C1

Abstract

An automatic brightness-control apparatus e.g. for a system for reflecting images into a microscope, maintains the same relationship between the brightness of a reticle or marking which is reflected-in and the microscopic image, in the observation plane, over the entire range of brightness values of the microscopic image.

Description

SPECIFICATION Brightness apparatus for a system for reflecting images into a microscope This invention relates to an apparatus for matching the brightness of markings which are reflected into the beam path of a microscope to the brightness of the microscopic image.

The technique of reflecting-in various symbols, grids, scales, etc., into the image-forming beam path of a microscope is known. The images are usually reflected-in by means of dividing mirrors or dividing prisms. The symbols or markings are transparent areas on otherwise opaque plates, which are back-illuminated by means of a light source. They accordingly appear as bright features in the image, on a background which may be light or dark, depending on the microscopy technique being used. The background is light if the bright-field method is used, being of midtone if the phase contrast or fringe contrast methods are used, and being dark, at least in part, if the polarization method, dark-field method, or fluorescence method is used.

Since the background can vary from very light to very dark, either in an eyepiece, or on a photograph on which the microscopic image is preserved, it is desirable to match the brightness of the reflected-in markings to the background, in order, on the one hand, to see the markings clearly, as a result of adequate brightness, and, on the other hand, to avoid the occurrence of glare and disturbances in the visibility of the microscopic image which accompany glare.

In the past, this brightness-matching has been carried out by manual control of the intensity of the light from the light source illuminating the markings to be reflected-in, for example with the aid of a potentiometer.

Since the brightness of the background can often change, it is inconvenient to have to continuously reajust the intensity of the light from the light source.

An object of the invention is to provide a solution to this problem, and to provide an apparatus, in which the brightness of an image which is reflected into the microscope is automatically matched to the brightness of the microscopic image.

According to the present invention we provide apparatus for matching the brightness of markings which are reflected-in a microscope to the brightness of the microscopic image, comprising a marking light source, a marking element and means to project an image from said marking element into the optical path of a microscope, control means for controlling the intensity of light from said marking light source, said control means comprising a photocell for measuring the brightness of the microscopic image, and as control circuit for controlling the supply of electric current to said marking light source as a function of the measured brightness, whereby the brightness ratio can be arraged to remain constant over the entire control range.

The control circuit preferably incorporates a nonlinear amplifier unit, a matching stage, and a power output stage for the marking light source. It is possible to provide, in the matching stage, a setting device for the purpose of setting a value which is constant over the entire control range and is to be added to the brightness of the light source, this brightness depending on the measured brightness value. It is also possible to provide a setting device for the purpose of setting a factor which is constant over the entire control range, which factor is multiplied by the brightness, this brightness depending on the measured brightness value. In both cases the setting device can be operated externally.

In the first case, care is taken to ensure that the markings which are reflected-in become visible even if the image is completely dark, while in the second case it is possible to adjust the ratio of the brightness of the reflected-in markings to the brightness of the background.

The circuit may also incorporate a microprocessor with a conversion program to achieve a similar result.

Further advantages, details and features of the invention will be evident from the following description, of a preferred illustrative embodiment, taken with reference to the drawings in which: Figure 1 is a diagrammatic representation of an arrangement for reflecting markings into the beam path of a microscope, for focussing for photography, and Figure 2 is a block diagram of a circuit which is used in conjunction with the apparatus shown in Fig. 1.

In Fig. 1, an object light beam 10, from the object 12, is split into a beam path 1 6 for direct viewing, and a beam path 1 8 for photography, by means of a beam-dividing surface 14. The direct viewing beam path 16, undergoes total reflection at the lower horizontal surface 20 of the prism 22, which also provides the beam-dividing surface 1 4.

The path of a marking beam is designated 24, this path leading from a marking light source 26 to the beam divider 14, via a collector lens 28, a grid 30 (or other reticle) and an image-forming lens 32. A camera 34 is provided with a lens 36. This arrangement is described in German Patent 2,361,692.

The film plane of the camera 34 is arranged in a plane which is conjugated with respect to the grid 30, of which images are formed simultaneously in the viewing and film planes by means of the image-forming lens and the beam divider. This makes it possible to use the back-illuminated grid for the purpose of focussing for photography. At the same time, as described in German Patent 2,361,692, the brightness of the light source is set manually, and matched to the background, with the aid of a potentiometer.

The microscopic image and the image of the grid are reflected by means of a mirror 38 which can be swung into, and out of, the beam path 1 8 used for photography. When the mirror is in the position shown in the drawing it reflects the beam into a photocell (not shown). The grid has virtually no disturbing effect on the measurement, since although it is brighter than the microscopic image, it nevertheless covers only a very small area.

The photocell, designated 40 in Fig. 2, emits an output signal to a matching stage 42, this signal corresponding to the measured brightness. The matching stage 42 emits, in turn, an output signal to a nonlinear amplifier unit 44, in which the output signal from the photocell 40 is converted in accordance with a defined function (for example, raised to the fourth power), in order to control power stage 46 which directly controls the brightness of the light source 26. The control is such that the brightness of the light source 26 changes in a way which, in subjective terms, is approximately proportional to the brightness of the microscopic image, it being possible to set both the brightness ratio and the reference brightness of the light source 26 in the matching stage 42, the brightness ratio being constant over the entire control range.The matching stage 42 could include a conventional comparator, such as a differential amplifier or other conventional comparator. Nonlinear amplifier 44 could include conventional devices such as log-antilog amplifiers, multiplying amplifiers, or even be converted to a digital signal which is then transformed by a power function and reconverted to an analog signal.

The invention can also be applied to other arrangements for combining images, for example systems for combining images in eyepieces, for measurement purposes, or in systems for combining images onto photographs, for documentation purposes. Furthermore, it is also possible to use a microprocessor, with a conversion program, instead of the nonlinear ampliier unit.

In the case described above, the mirror 38 and the photocell 40 are, for example, also used for controlling the exposure-setting of the camera. In other cases, particularly in cases which do not involve the use of a camera, a separate photocell would then have to be provided.

Claims

1. Apparatus for matching the brightness of markings which are superimposed on a microscope image to the brightness of the microscopic image, comprising a reticle light source, a reticle and means to project an image from said reticle into the optical path of a microscope, control means for controlling the intensity of light from said reticle light source, said control means comprising a photocell for generating a signal representative of the measure the brightness of the microscopic image and a circuit means for regulating the electrical source of current to said reticle light source in response to said signal, whereby the relative brightness of the reticle remains constant.

2. Apparatus according to Claim 1, in which said circuit means includes a nonlinear amplifier unit, a matching stage, and a power output stage for the marking light source.

3. Apparatus according to Claim 2, in which an adjustment device is provided in the matching stage to set a chosen value which is constant over the entire control range and is to be added to the brightness of the marking light source, this brightness depending on the brightness value as measured by the photocell.

4. Apparatus according to Claim 2, in which a adjustment device is provided, in the latching stage to set a factor which is constant over the entire control range and is to be multiplied by the brightness of the marking light source, this brightness depending on the brightness value as measured by the photocell.

5. Apparatus according to Claim 1, in which the control circuit includes a microprocessor with a conversion program.

6. Apparatus for matching the brightness of markings substantially as herein described with reference to the accompanying drawings.