SU932341A1 - Method of determination of focal length and rear focus position of an optical system - Google Patents

Description

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The invention relates to optical instrument making and can be used to determine the focal distance and the position of the back focus of a predominantly long focal onTHHedKoft system. The most important area of application is optical heterodyning, where high accuracy of installation in the back focus of the system (in the plane of the Erie circle) of the heterodyne photodetector is required.

A goniometric method for measuring focal lengths of optical systems is known, which is most commonly used for long-focus systems.

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The closest to the present invention is a method for determining the focal distance and the position of the back focus of the optical system, which consists in obtaining a sharp autoplimaion image of a light source during a double passage of a light beam through the test system when it is reflected from one of the two surfaces of the auxiliary optical element, fixing of this image and measurement of the equivalent optical power of the system under test n the auxiliary element f2j.

However, this method does not allow simultaneously determining the position of the back focus of the optical system to determine the value of its focal distance 10. In addition, the accuracy of determining the position of the back focus depends on the accuracy of manufacturing the flat surface of the mirror, which is especially difficult for high-aperture systems.

15 technological challenge. In practice, flat surfaces are made of spheres with curvature radii, tens of meters and kilometers in the air. This increase in the accuracy of fixing the position of the autoclipped glare and the statistical processing of measurements cannot eliminate the systematic error caused by the curvature of the mirror surface.

The circuit of the invention is to increase the measurement accuracy when monitoring various types of optical systems.

This goal is achieved by fixing a sharp auto-image from the second reflecting surface of the auxiliary optical element while nudging the same test system, measuring the distance between the sharp auto-improper images obtained with the participation of each of the surfaces of the auxiliary optical element, and then the focal length and the back focus position of the optical system under test are calculated.

The drawing shows one of the variants of the optical device that implements this method.

The radiation from the illuminator 1 illuminates the auto-plasma grid 2, is reflected from the beam-splitting surface of the light-splitting device 3, passes the optical system under test 4, reflects from one of the surfaces of the auxiliary lens 5 and returns through the optical system 4 and the beam-splitting device 3, builds the image of the autoplimation grid 2 near the plane of the grid 6 of the autocollimation block 7. The analyzing device 8 determines the degree of sharpness of the image in the plane of the grid 6. Index 9 of the reading device 10 gesture connected to the grid 6. Moving the autocollimation unit 7 along the axis using an analyzing device 8, find the position of the sharp image of the grid -2 in the plane of the grid 6 and register it with a reading device that allows determining the movement of the grid 6 along the optical axis.

The advantage of the proposed method in comparison with the known ones can be seen from the following example of measuring the parameters of a lens with a focus of 17.7 m. The standard error of the angle measurements by a theodolite is 0, 5, which leads to an error in calculating the focal length of 7.6 mm.

To find the position of the back focus of the system using a known autoplimation method, we used a reflective glass surface of glass paste with a distance of 0.08 rings over a diameter of 1-20 mm, which corresponds to a radius of curvature of 8 km. As a result of the influence of the spherical surface of the plate, the position of the back focus is obtained with an error of 4 mm. When measuring the method of the proposed method, two plane-parallel glass plates were used, which, due to the sphericity of the surfaces, are long-focus lenses. | The following deviations from the fglandity are given: 1 plate -1.3 rings and 0, O8 rings; 2 plate - 0,13 rings and 0,22 rings.

The measurements are carried out on the proposed method using the device (Fig. 1). For the calculations, we used the formulas given below that make up the system

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de D is the difference of the readings of the first and each of the subsequent readings;

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Csg-g values are inversely proportional to the distance from the rear main point of the lens to the axial point of the autoplimation image corresponding to the first dimension; F is the optical power of the lens; R IR - the radii of curvature | s of the first and second surfaces of the first lens;

Claims (2)

R nR.- radii of curvature of the first and second surfaces;) of the second lens; db.judfe is the distance between the front main point of the lens and the surfaces of the first and second pi facing the lens; the tops of the first and second, are indications of the precomposition of the materials of the first and second piné for the working wavelength. The advantage of the proposed method is to reduce the laboriousness of work on measuring the magnitude of the focal distance and recording the back focus. The invention of the method for determining the magnitude of the focal distance and the position of the back focus of the optical system, which consists in obtaining a sharp autocollimation image of the light source when the light beam passes twice through the test system when reflected from one of the two surfaces of the auxiliary optical element fixing this image and measuring equivalent optical power of the tested system and auxiliary element, differ. In order to increase the accuracy of measurements when monitoring various types of optical systems, they fix a sharp autoplimation image from the second reflecting surface of the auxiliary optical element in the presence of the same test system, measure the distance between the sharp auto-optic images obtained with the participation of each of the surfaces of the auxiliary optical element and then calculate the magnitude of the focal distance and the position of the back focus of the optical system under test. Sources of information taken into account in the examination 1. Krivov and L. M., et al. Practice of the Optical Measuring Laboratory, M., Mashchinostroenie, 1974. 2. Afanasyev V, A. Optical changes, M, Nedra, 1968 (prototype). M