DE2229761A1 - PROCEDURE FOR DETERMINING THE PLANE OF FOC - Google Patents

Description

ERNST LKITZ QMBH

Our reference: A 1863 / B 2731 633 Wetelar, den. ' _T.

Pat Se / GG HMmkmim ¹ ^ * ^June

Procedure for defining the plane of focus

The invention relates to a method for defining the focal plane of a system designed by an imaging system Image with photoelectric means and devices for carrying out the method.

There are automatic focusing devices for optical systems are known in which an image through an optical System is designed on an observation field that is movable relative to it. Connected to the optical system is a shifting device with which the image is focused on the moving observation field. These Displacement device is controlled by the output signals of two on the same side of the observation field spaced photoelectric receiver, in such a way that these receivers point to different from the optical system even during a relative movement The beam components designed between the image and the system respond after the output signals of the receiver have a Have passed through the comparison stage. This comparison level only emits a maximum output signal when the optical system is optimally focused. The focus isn't optimally, the correspondingly smaller signal controls the displacement device, preferably in terms of signal optimization. In the moving observation field there is a one that can be moved in a defined manner and is provided with apertures Component.

The present invention is based on the object of the known To improve facilities so that through

309862/0768

A 186-3 / B 2731

June 15, 1972.

optimal adaptation to the characteristics of what is available as an object Image structures and the almost complete utilization of the light involved in image generation are both the area of application for the focusing device as well as its accuracy of the focal plane capture increased.

The invention accordingly relates to a method of the type mentioned at the beginning, which is characterized in that, about components of all azimuths and spatial frequencies of image structures to make it usable for the evaluation in the plane of a measuring field, in the measuring field scattering structures of such widths and lengths are arranged so that the spectrum of spatial frequencies of the scattering structure present in the measuring field is almost contains only spatial frequencies that are to be optimized during focusing, by pupil sections correspond to the spatial frequency range represented from the imaging aperture, and that the distance between the imaging System and the measuring field level is changed according to amount and direction until the amount is reached in the image field level Modulation transfer function of the imaging system in the measuring field level, averaged over the by the Scatter structures given spatial frequency range, maximum values for the image field section involved in the measurement accepts.

Advantageous refinements of the method and devices for carrying it out are set out in the subclaims marked «

The invention is explained below with reference to a schematic drawing »

An imaging optical system 1 to be focused can be moved by a servo member 2 for focusing on scattering structures 3 along its optical axis, that of

3Ü9882 / 0768

_ Q

A I863 / B 2 / T1

^{1S 6 1972} 2229761

Light incident on the left and carrying the information from the desired object plane passes through the system 1 onto the scattering structure 3, which can be moved by means of a drive 3 ^f, preferably perpendicular to the optical axis of the system 1. This scattering structure 3 is assigned two photoelectric receivers 4, 5 which are symmetrical to the optical axis and to which radiation components from only incompletely overlapping surface elements of the pupil of the system 1 are fed separately. The output signals of the receivers 4, 5 are fed to separate inputs of a comparison stage 6 after appropriate amplification.

In the comparison stage 6, the two signals are as Difference or quotient combined in such a way that one is dependent on the difference in focus between the image and the scattered structure Output signal results in «The sign of the output signal is due to the modulation of the interlinked signals of the receivers 4 and 5 with a reference signal obtained which phase-locked to the movement of the carrier of the scattering structures 3, preferably from the control signal for the drive 3 * is obtained. This output signal is used in a known manner to control the distance between the system 1 and the spreading structure 3 by means of the servo element 2 used.

The function of the device described so far is as follows: the image structure to be focused and the measuring field structure 3 are set in relative movement to one another parallel to their planes by means of the drive 3 '. the The resulting amplitude and phase relative to the movement phase of the scatter structure 3 of the from the signals of two receivers 4, 5 formed signal is a measure of the amount and sign of the distance between the image plane and Auxiliary structure level. If both levels coincide, then it takes the signal in the comparison stage shows an extreme value.

309882/0768

A 1863 / B 2731

Even blaze effects caused only by phase objects and different intensities in the pupil parts can result in the Finding extreme values largely through the drive 3 'caused modulation in the alternating signals in the Separation of the constant light current component eliminated.

Instead of the structural plane moved in a coordinate direction parallel to it, an arrangement can also be provided be, in which this plane is moved in two preferably mutually perpendicular coordinate directions. In this case, further photoelectric receivers and a comparison stage must be available. Such an arrangement makes sense if the object has structures that are parallel to the first-mentioned coordinate direction.

It goes without saying that devices for carrying out the method according to the invention can be used in various ways use in practice. So the output signal of the comparison stage 6, for example, control the focusing or the distance measurement with the lens 1, or it can When searching in the room, ensure that with a fixed Focus of the system 1 on the measuring field only images of object elements are thrown, all on a curve the same distance.

The scatter structure is for optimal use of the image light flow preferably a non-absorbing phase structure with a phase deviation of - for the spectral focus of the imaging light. The sum of the area proportions that influence the radiation in terms of a phase advance, is preferably chosen to be equal to the sum of the surface fractions which the radiation in the sense of a phase delay influence in order to extinguish light which passes through the scattering structure directly through interference.

-5-

309882/0768

Claims (1)

A T863 / B 2731 June 15, 1972 Expectations Process for the photoelectrical definition of the focal plane an image designed by an imaging system, characterized in that, around components of all azimuths and spatial frequencies of image structures to make them usable for the evaluation in the plane of a measurement field, in the measurement field scatter structures (3) such Latitudes and lengths are arranged so that the spectrum of the spatial sequence of the scatter structure present in the measuring field almost exclusively contains spatial frequencies that are to be optimized during focusing Represented pupil sections from the imaging aperture Spatial frequency range correspond, and that the distance between the imaging system (1) and the measuring field plane is changed according to amount and direction until the amount of the modulation transfer function reached in the image field plane of the imaging system (i) in the measuring field plane, averaged over the area caused by the scattering structures given spatial frequency range, maximum values for the image field section involved in the measurement accepts 2ο method according to claim 1, characterized in that a measurement field is defined in a manner known per se in the image plane or in a plane conjugate to it whose dimensions are sufficiently small to separate an object detail which focuses optimally is mapped into the plane of the measuring field. 3. The method according to claim 1 and 2, wherein from the pupil of the imaging system to be focussed in pairs symmetrical to the optical axis of the imaging system, only incompletely overlapping surface elements assigned radiation components either two equivalent photoelectric converters at the same time be fed geometrically, or in which the feed 309882/0768 ~ ⁶ ~ A 1863 / B 2731 June 15, 1972. 2223761 the radiation components take place alternately one after the other to a single photoelectric converter, thereby characterized in that the image structure to be focused and the measuring field structure (3) in one or two coordinate directions lying parallel to their planes are offset in relative movement to one another and that the amplitude of the difference or quotient signal between the two converters (4, 5) or the alternating signal sequence from the one receiver as a measure of the amount of the distance between the image plane and plane of the measuring field is evaluated and that the sign of the distance by the phase-related Modulation between a reference signal coupled with the relative movement and the linked measurement signals is won. Method according to Claim 3 »in which the local frequency range, to which the measurement relates and the range of relative speeds between the image plane and measuring field is limited, characterized in that the signal frequency range is limited such that a signal frequency filter with its phase shifting Band edges are still sufficiently far removed from that given by the corresponding spatial frequency range Useful signal spectral range is to ensure phase-correct difference or quotient formation. Method according to claims 1 to k, characterized in that, for better separation of the electrical measurement signals from the storm signal components and to obtain the sign of the storage, these measurement signals are electrically cross-correlated with a sum signal obtained from the respective pairs of converter signals, with the help of further photoelectric converters to the Sum measurement signal an additional push-pull signal is obtained, which is switched in difference to the sum measurement signal, -7- 309882/0768 A T863 / B 2731 June 15, 1972. and that the resulting signal is then fed to a comparison stage (6) as a reference signal. 6. The method according to claim 5t, characterized in that if there are phase structures of the auxiliary structure (3), the additional push-pull signal in the case of restriction of the effective pupil areas by utilizing separate, preferably non-overlapping diffraction angle ranges through the phase syncxKRgK between different ones Diffraction orders is obtained. 7 · Method according to one of the preceding claims, characterized characterized in that, if the use of an objective (1) to achieve one for the depth resolution due to special reasons, the measurement in already proposed in two or four identical, with a fixed base to each other Lenses are distributed that cut out the pupil "correspond when generating a mixed image from at least two sub-image fields. 8. The method according to any one of the preceding claims, characterized characterized in that in a manner known per se using a servo drive fed by the measurement signal (2) When searching in space, images of object elements are thrown onto the measuring field, which all lie on a curve of equal distance, being in the scanned space up to distances that are very are large compared to the focal length of the imaging system, intersection lines on surfaces of equal distance be placed. 9 »Device for carrying out the method according to claim 5, characterized in that when using scattering structures (3) in the form of one- or two-dimensional 309882/0768 A 1863 / B 2731 June 15, 1972. 2229761 Grid structure with a very pronounced fundamental frequency a phase-sensitive rectifier is used as a comparator (6) in a manner known per se, which by an auxiliary signal derived from the same auxiliary grid structure and corresponding to its spatial frequency is controlled. 10. Device for performing the method according to claim 1, characterized in that the lens for transmission A diaphragm is assigned to the high spatial frequencies, which is symmetrical to the optical axis Pairs of circular triangles with one another of the same size as passages, the radii of which correspond to the radius of the Corresponding to circular disc and cling to its circumference. 11. Device for performing the method according to claim 1, characterized in that the scattering structures (3) in the measuring field are phase structures whose phase shift with effectively r · are adapted to the wavelength center of gravity of the imaging light and that the phase-shifting area shares around $ 50 of the measuring field. 12. Device for performing the method according to one of claims 1 to 8, characterized in that in In a known manner, with a component moved by the servo drive, an output device for the measured distance value of the appropriate object. 309882/0768