CN108873566B - Design method of lens hood of low-light level camera in field of view - Google Patents

Design method of lens hood of low-light level camera in field of view Download PDF

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CN108873566B
CN108873566B CN201810622423.5A CN201810622423A CN108873566B CN 108873566 B CN108873566 B CN 108873566B CN 201810622423 A CN201810622423 A CN 201810622423A CN 108873566 B CN108873566 B CN 108873566B
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field
low
view
camera
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CN108873566A (en
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张庭成
刘晓林
李可
李洋
赵健
刘芳芳
阮宁娟
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Beijing Institute of Space Research Mechanical and Electricity
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
    • G03B11/00—Filters or other obturators specially adapted for photographic purposes
    • G03B11/02—Sky masks
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/0012—Optical design, e.g. procedures, algorithms, optimisation routines

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Abstract

A design method of a lens hood of a low-light level camera in a field of view relates to the technical field of space remote sensing; the method comprises the following steps: step one, calculating shading of low-light level camera in biased view fieldThe rejection ratio of the shroud; calculating the length L of a shading cover of the low-light level camera in the offset field of view; step (III) according to the upper boundary of the bias view field micro-optic camera as LUp1(ii) a Calculating the upper bound L of the shadeUp2(ii) a Step (IV), setting the lower boundary of the bias view field of the low-light-level camera in the bias view field to be LDw1(ii) a Calculating the lower boundary L of the light shieldDw2(ii) a Step five, according to the calculation results of the step three and the step four, modeling of the light shield is completed; the invention realizes the imaging requirements of the low-light-level camera on high sensitivity and large dynamic range, can be applied to the design of the star sensor camera lens hood, and has higher transportability and universality.

Description

Design method of lens hood of low-light level camera in field of view
Technical Field
The invention relates to the technical field of space remote sensing, in particular to a design method of a low-light-level camera lens hood in a field of partial vision.
Background
A high-sensitivity and large-dynamic-range low-light-level camera belongs to a low-light-level signal detection system under a strong stray light background, has high requirements on the suppression level of the stray light, and generally has higher requirements on a star sensor camera. However, in the case of an off-field use, the asymmetry of the field of view is not considered in the existing design method, the arrangement of the light blocking ring inside the light shield still follows the integrated design under the condition of a symmetric field of view, the light blocking ring is not divided into two parts, and the design of the upper and lower groups of light blocking half rings is respectively carried out, so that the matching of the inner light blocking ring and the asymmetric field of view cannot be ensured. In order to solve the above problems, the present invention provides a design method for a light shield based on an asymmetric field of view, which can arrange an upper set of light-blocking half rings and a lower set of light-blocking half rings in the light shield in an asymmetric manner, so as to ensure that the light-blocking rings of the light shield can be strictly matched with the asymmetric field of view.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, provides a design method of a light shield of a low-light-level camera in an off-field, meets the imaging requirements of the low-light-level camera on high sensitivity and large dynamic range, can be applied to the design of the light shield of the star sensor camera, and has higher transportability and universality.
The above purpose of the invention is realized by the following technical scheme:
a design method of a light shield of a low-light level camera in a field of view comprises the following steps:
step one, measuring the minimum incident angle alpha of the stray light sourceMIN，αMINSuppressing the angle for the stray light of the low-light camera in the field of view; measuring to obtain the lower limit L of the dynamic range of the low-light level camera in the field of viewMINMeasuring the energy E of the stray light sourceSLCalculating the suppression ratio of a lens hood of the low-light camera in a field of view;
step (II), measuring to obtain the maximum diagonal half-field omega of the low-light-level camera in the field of viewDiaMeasuring to obtain the light entrance aperture D of the first lens, measuring the reflection times n of the stray light in the lens hood and the stray light suppression angle alpha of the low-light level camera in the field of viewMINCalculating the length L of a lens hood of the low-light camera in the field of view; n is 1 or 2;
setting the upper boundary of the deflection field micro-optic camera to be LUp1(ii) a Calculating the upper bound L of the shadeUp2；
Step (IV), setting the lower boundary of the bias view field low-light level camera to be LDw1(ii) a Calculating the lower boundary L of the light shieldDw2；
And (V) finishing modeling of the light shield according to the calculation results of the step (III) and the step (IV).
In the above method for designing a mask of a low-light level camera in a field of view, in the step (i), the method for calculating the rejection ratio of the mask of the low-light level camera in the field of view includes:
Figure BDA0001698363590000021
wherein τ is a transmittance of a predetermined optical system;
u′0the central view field image space aperture angle is preset;
p is the ratio of the maximum stray energy illumination value to the imaging energy illumination value, and p is 0.1.
In the above method for designing a lens hood of a low-light level camera in a field of view, in the step (ii), the method for calculating the length L of the lens hood of the low-light level camera in the field of view includes:
s1: when n is equal to 2, the compound is,
Figure BDA0001698363590000022
s2: when n is equal to 1, the compound is,
Figure BDA0001698363590000023
in the above design method of the lens hood of the low-light-level camera in the field of view, in the step (iii), the upper boundary L of the lens hoodUp2The calculation method comprises the following steps:
measuring to obtain critical stray light CD reaching the lower side of a first lens of the camera; then L isUp1The intersection point M1 with the CD is the position of the first upper light-blocking half ring; setting the foremost end of the lower boundary of the offset field as F, reflecting the light FM1 through the N1 point of the upper boundary of the mask and LUp1Intersecting with M2, wherein M2 is the position of the second upper light-blocking half ring; the light FM2 is reflected by the N2 point on the upper boundary of the shade and then is reflected with LUp1Intersecting with M3, M3 is the position of the third upper half light-blocking ring, and so on until the coordinates of the reflection point is greater than the length L of the light shield.
In the above method for designing a lens hood of a low-light level camera in a field of view, in the step (iv), the lower boundary L of the lens hoodDw2The calculation method comprises the following steps:
measuring to obtain critical stray light AB reaching the upper side of a first lens of the camera; then L isDw1The intersection point P1 with AB isThe position of the first lower light-blocking half ring; setting the foremost end of the lower boundary of the squint field as E; the light EP1 is reflected by the point Q1 at the lower boundary of the mask and is reflected by the point LDw1Crossing with P2; p2 is the position of the second lower light-blocking half ring; the light EP2 is reflected by the point Q2 on the upper boundary of the shade and then is reflected by the point LDw1Intersecting with P3, where P3 is the position of the third lower light-blocking half ring; and the like until the coordinate of the reflection point is larger than the length L of the light shield.
In the above method for designing a lens hood of a low-light-level camera in a field of view, in the second step, when n is 1, it indicates that 1 reflection occurs on the inner wall of the lens hood for the stray light incident on the lens hood; when n is 2, it indicates that the stray light incident on the mask is reflected 2 times on the inner wall of the mask.
In the above method for designing a lens hood of a low-light level camera in a field of view, in the second step, the incident angle of the stray light is greater than or equal to the suppression angle.
In the above design method of the light shield of the low-light level camera in the field of view, the light blocking ring inside the light shield includes two half rings which are independent from each other.
Compared with the prior art, the invention has the following advantages:
(1) the invention pertinently considers the influence of the asymmetry of the deviated view field on the design of the high-sensitivity large-dynamic-range micro-light camera lens hood, and adopts a method for designing the light blocking half rings in the lens hood in a grouping manner because the design of the integrated light blocking ring cannot be carried out, thereby meeting the strict matching between the light blocking half rings and the asymmetric view field and improving the utilization efficiency of the light blocking rings;
(2) the invention provides a method for establishing the relation between the reflectivity of each surface of the inner wall of a light shield and the inhibition ratio based on light ray tracing, aiming at the problem that the reflectivity of different types of surfaces of the inner wall of an asymmetric light shield cannot be uniformly set, and the reflectivity is designed according to the influence of each surface of the inner wall of the light shield on the inhibition ratio of the light shield.
Drawings
FIG. 1 is a flow chart of the design of a light shield according to the present invention;
FIG. 2 is a schematic view of the light-blocking half ring design according to the present invention.
Detailed Description
The invention is described in further detail below with reference to the following figures and specific examples:
the invention provides a design method of a glimmer camera lens hood in an off-normal field, which is used for designing the glimmer camera lens hood with off-normal field, high sensitivity and large dynamic range. And in order to solve the problem that the reflectivities of different types of surfaces and asymmetric light blocking half rings cannot be uniformly set, the relationship between the surfaces of the inner walls and the suppression ratio of the light shield is established one by a light ray tracing method, so that the setting of the reflectivities of the surfaces of the inner walls is completed.
The method is used for designing the light shield of the low-light-level camera with the biased view field, can ensure the imaging requirements of the low-light-level camera on high sensitivity and large dynamic range, can be applied to the design of the light shield of the star sensor camera, and has higher transportability and universality.
As shown in fig. 1, which is a flow chart of designing a light shield, it can be known that a method for designing a light shield of a low-light-level camera in a field of view includes the following steps:
step one, measuring the minimum incident angle alpha of the stray light sourceMIN，αMINSuppressing the angle for the stray light of the low-light camera in the field of view; measuring to obtain the lower limit L of the dynamic range of the low-light level camera in the field of viewMINMeasuring the energy E of the stray light sourceSLCalculating the suppression ratio of a lens hood of the low-light camera in a field of view;
the method for calculating the suppression ratio of the lens hood of the low-light-level camera in the field of view comprises the following steps:
Figure BDA0001698363590000041
wherein τ is a transmittance of a predetermined optical system;
u′0the central view field image space aperture angle is preset;
p is the ratio of the maximum stray energy illumination value to the imaging energy illumination value, and p is 0.1.
Minimum angle alpha of incidence of the astigmatic light source in step (a)MINEnergy E of astigmatic light sourceSLOn-track status parameters for queryable cameras; lower limit of camera dynamic range LMINThe camera focal plane electronic parameters can be inquired; the ratio p of the maximum value of the stray energy illumination to the illumination value of the imaging energy is an empirical value
Step (II), measuring to obtain the maximum diagonal half-field omega of the low-light-level camera in the field of viewDiaMeasuring to obtain the light entrance aperture D of the first lens, measuring the reflection times n of the stray light in the lens hood and the stray light suppression angle alpha of the low-light level camera in the field of viewMINCalculating the length L of a lens hood of the low-light camera in the field of view; n is 1 or 2;
the method for calculating the length L of the lens hood of the low-light-level camera in the field of partial view comprises the following steps:
s1: when n is equal to 2, the compound is,
Figure BDA0001698363590000051
s2: when n is equal to 1, the compound is,
Figure BDA0001698363590000052
when n is 1, the stray light incident on the light shield is reflected for 1 time on the inner wall of the light shield; when n is 2, the stray light incident on the light shield is reflected for 2 times on the inner wall of the light shield; the incidence angle of the stray light is larger than or equal to the inhibiting angle.
And step (III), the light blocking ring in the light shield comprises two semi-rings which are independent from each other up and down. Setting the upper boundary of the bias view field low-light level camera to be LUp1(ii) a Calculating the upper bound L of the shadeUp2；
Upper boundary L of the light shieldUp2The calculation method comprises the following steps:
measuring to obtain critical stray light CD reaching the lower side of a first lens of the camera; then L isUp1The intersection M1 with the CD is the first gear-upThe position of the photo half ring; setting the foremost end of the lower boundary of the offset field as F, reflecting the light FM1 through the N1 point of the upper boundary of the mask and LUp1Intersecting with M2, wherein M2 is the position of the second upper light-blocking half ring; the light FM2 is reflected by the N2 point on the upper boundary of the shade and then is reflected with LUp1Intersecting with M3, M3 is the position of the third upper half light-blocking ring, and so on until the coordinates of the reflection point is greater than the length L of the light shield.
Step (IV), setting the lower boundary of the bias view field low-light level camera to be LDw1(ii) a Calculating the lower boundary L of the light shieldDw2；
Lower boundary L of the light shieldDw2The calculation method comprises the following steps:
measuring to obtain critical stray light AB reaching the upper side of a first lens of the camera; then L isDw1The intersection point P1 with AB is the position of the first lower light-blocking half ring; setting the foremost end of the lower boundary of the squint field as E; the light EP1 is reflected by the point Q1 at the lower boundary of the mask and is reflected by the point LDw1Crossing with P2; p2 is the position of the second lower light-blocking half ring; the light EP2 is reflected by the point Q2 on the upper boundary of the shade and then is reflected by the point LDw1Intersecting with P3, where P3 is the position of the third lower light-blocking half ring; and the like until the coordinate of the reflection point is larger than the length L of the light shield.
Critical stray light AB and CD are the optical machine design result capable of being inquired, and the upper and lower boundaries L of the light shieldUp2And LDw2Boundary input conditions designed for a low-light camera lens hood in an off-field are used to limit the size of the lens hood, the upper and lower boundaries L of the off-fieldUp1And LDw1For queryable optical design results
Step five, according to the calculation results of the step three and the step four, modeling of the light shield is completed; and (5) performing ray tracing to determine the reflection coefficient of the inner wall of the light shield by taking the suppression ratio calculated in the step (I) as a threshold value.
An optical machine model is established in stray light analysis software, light ray tracing is carried out, energy at an inlet and an outlet of the light shield is obtained, the energy value at the outlet is divided by the energy value at the inlet to obtain the suppression ratio of the light shield, if the suppression ratio is larger than a threshold value determined by the formula (1), the reflectivity inside the light shield is reduced until the suppression ratio is smaller than the threshold value, and the embodiment finally determines that the reflectivity inside the light shield is 7%.
Those skilled in the art will appreciate that those matters not described in detail in the present specification are well known in the art.

Claims (4)

1. A design method of a lens hood of a low-light level camera in a field of view is characterized by comprising the following steps: the method comprises the following steps:
step one, measuring the minimum incident angle alpha of the stray light sourceMIN，αMINSuppressing the angle for the stray light of the low-light camera in the field of view; measuring to obtain the lower limit L of the dynamic range of the low-light level camera in the field of viewMINMeasuring the energy E of the stray light sourceSLCalculating the suppression ratio of a lens hood of the low-light camera in a field of view;
step (II), measuring to obtain the maximum diagonal half-field omega of the low-light-level camera in the field of viewDiaMeasuring to obtain the light entrance aperture D of the first lens, measuring the reflection times n of the stray light in the lens hood and the stray light suppression angle alpha of the low-light level camera in the field of viewMINCalculating the length L of a lens hood of the low-light camera in the field of view; n is 1 or 2;
setting the upper boundary of the deflection field micro-optic camera to be LUp1(ii) a Calculating the upper bound L of the shadeUp2；
Step (IV), setting the lower boundary of the bias view field low-light level camera to be LDw1(ii) a Calculating the lower boundary L of the light shieldDw2；
Step five, according to the calculation results of the step three and the step four, modeling of the light shield is completed;
in the step (one), the method for calculating the suppression ratio of the lens hood of the low-light-level camera in the off-field comprises the following steps:
Figure FDA0002587941800000011
wherein τ is a transmittance of a predetermined optical system;
u′0the central view field image space aperture angle is preset;
p is the ratio of the maximum value of stray energy illumination to the imaging energy illumination value, and p is 0.1;
in the step (two), the method for calculating the length L of the lens hood of the low-light-level camera in the off-field comprises the following steps:
s1: when n is equal to 2, the compound is,
Figure FDA0002587941800000012
s2: when n is equal to 1, the compound is,
Figure FDA0002587941800000021
in the third step, the upper boundary L of the light shieldUp2The calculation method comprises the following steps:
measuring to obtain critical stray light CD reaching the lower side of a first lens of the camera; then L isUp1The intersection point M1 with the CD is the position of the first upper light-blocking half ring; setting the foremost end of the lower boundary of the offset field as F, reflecting the light FM1 through the N1 point of the upper boundary of the mask and LUp1Intersecting with M2, wherein M2 is the position of the second upper light-blocking half ring; the light FM2 is reflected by the N2 point on the upper boundary of the shade and then is reflected with LUp1Intersecting with M3, wherein M3 is the position of the third upper light-blocking half ring, and repeating the steps until the coordinate of the reflection point is greater than the length L of the light shield;
in the step (IV), the lower boundary L of the light shieldDw2The calculation method comprises the following steps:
measuring to obtain critical stray light AB reaching the upper side of a first lens of the camera; then L isDw1The intersection point P1 with AB is the position of the first lower light-blocking half ring; setting the foremost end of the lower boundary of the squint field as E; the light EP1 is reflected by the point Q1 at the lower boundary of the mask and is reflected by the point LDw1Crossing with P2; p2 is the position of the second lower light-blocking half ring; the light EP2 is reflected by the point Q2 on the upper boundary of the shade and then is reflected by the point LDw1Intersecting with P3, where P3 is the position of the third lower light-blocking half ring; and the like until the coordinate of the reflection point is larger than the length L of the light shield.
2. A method for designing a light shield of a low-light level camera according to claim 1, wherein: in the second step, when n is 1, the stray light entering the light shield is reflected for 1 time on the inner wall of the light shield; when n is 2, it indicates that the stray light incident on the mask is reflected 2 times on the inner wall of the mask.
3. A method for designing a light shield of a low-light level camera in a field of view according to claim 2, wherein: in the step (II), the incident angle of the stray light is larger than or equal to the inhibiting angle.
4. A method for designing a light shield of a low-light level camera according to claim 3, wherein: the light blocking ring in the light shield comprises two semi-rings which are independent from each other up and down.
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