CN103033344B - Optical system focal distance detection method - Google Patents
Optical system focal distance detection method Download PDFInfo
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- CN103033344B CN103033344B CN201210544399.0A CN201210544399A CN103033344B CN 103033344 B CN103033344 B CN 103033344B CN 201210544399 A CN201210544399 A CN 201210544399A CN 103033344 B CN103033344 B CN 103033344B
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Abstract
The invention discloses an optical system focal distance detection method and belongs to the technical field of optics. The method includes the following steps that moire fringes are formed after light of a light source penetrates through a target board and change divergent light of the target light to parallel light after passing through a collimator, and after the parallel light passes through a shot under a test, a target is image-formed on a focal plane of the shot under the test; a time delay and integration charge coupled device (TDICCD) is configurated through a computer, driving frequency fT of a line transfer pulse signal of the TDICCD is confirmed, from image motion linear speed people can know that the driving frequency fT of the line transfer pulse signal has a proportional relation to the image motion linear speed, when the computer controls the TDICCD to start rotation from an initial position, the line transfer pulse signal is sent, images are started to be recorded, when the TDICCD reaches to an ending position, the images are stopped being recorded, and the line transfer pulse signal is stopped being sent. Under the speed, a precise rotating platform is driven to take pictures for 4-5 times, and focal distance of the shot under the test is calculated. The optical system focal distance detection method is high in detection accuracy and widely applied to detection on focal distance of optical system of optical instrument equipment.
Description
Technical field
The present invention relates to a kind of optical system focal distance detection, belong to optical technical field.
Background technology
The focal length of optical system is one of main parameter of optical instrumentation, and its precision directly affects the image quality of equipment.Focal length actual value after optical system alignment and design load have certain deviation, general employing magnification method and angle-measuring method measure optical system, magnification method measurement standard difference theoretical value is 0.3%, angle-measuring method measurement standard difference theoretical value is 0.06%, but in actual measurement, the focal length of system under test (SUT) debugs the impact of level, the errors of principles and reading error etc. factors by environmental factor, human factor, technology, makes the measurement error of these two kinds of method focal lengths all be not less than 2%.The impact of this measuring error on short-focus lens is less, but is significant for the impact of long focal length optical instrument.For the camera lens more than 1.5m focal length, the error of 2% can cause the very fast of image quality decrease.Therefore, the detection of optical system focal length is very important.
Summary of the invention
For background technology Problems existing, the invention provides a kind of optical system focal distance detection, concrete steps are as follows:
Step one, the light source selecting brightness uniformity, contrast are that the 4# standard resolution chart of 1000:1 is as Target Board, Target Board is carved with the grating fringe of 25 groups of different space frequency, Moire fringe is formed after the light therethrough Target Board that light source sends, after being placed on the parallel light tube on air floating platform, the diverging light of Target Board is become directional light, directional light is by after tested camera lens, and target imaging is on the focal plane of tested camera lens;
On step 2, precise rotating platform that tested camera lens and TDICCD are placed on, tested camera lens is placed on precise rotating platform center, TDICCD places the edge of precise rotating platform, and overlap with the focal plane of tested camera lens, connect TDICCD power supply, utilize computing machine to be configured TDICCD, determine the driving frequency f of the capable transfer pulse signal of TDICCD
t, move linear velocity, row transfer pulse signal driving frequency f from picture
tthe proportional relation of linear velocity v is moved with picture,
According to formula
1.,
2. with the bigness scale focal length of tested camera lens
with error range Δ f, estimate the range of speeds of precise rotating platform
;
Step 3, in the velocity range of precise rotating platform set a velocity amplitude, turntable controller inputs precise rotating platform and rotates reference position, end position and velocity amplitude, precise rotating platform is driven steadily to rotate from reference position, stop motion during arrival end position, and correcting action, when computing machine control TDICCD rotates from reference position, send row transfer pulse signal, and start to record image, when arriving end position, stop record image and send row transfer pulse signal;
Step 4, drive precise rotating platform with the speed set in step 3, take pictures from reference position steadily rotates, stop taking pictures when arriving end position, and correcting action, record image, this process repeats 4 ~ 5 times, to obtain 4 ~ 5 width images;
Step 5, reading images carry out comprehensive interpretation, judge whether image exists on TDI direction and differentiate decay, if image being decayed without differentiating on TDI direction, can think that this speed is mated with line frequency, 2. calculating tested lens focus by formula; If image exists larger resolution decay on TDI direction, select speed recruitment according to attenuation degree, repeat step 3 and step 4; Through m test, the best resolution image of final acquisition, calculates tested lens focus.
Beneficial effect of the present invention: the present invention utilizes image motion velocity matching principle to detect focal length, by determining the driving frequency f of the capable transfer pulse signal of TDICCD
t, move linear velocity, row transfer pulse signal driving frequency f from picture
tthe proportional relation of linear velocity v is moved with picture,
According to formula
1.,
2. with the bigness scale focal length of tested camera lens
with error range Δ f, estimate the range of speeds of precise rotating platform
; When computing machine control TDICCD rotates from reference position, send row transfer pulse signal, and start to record image, when arriving end position, stop record image and send row transfer pulse signal; Drive precise rotating platform to take pictures under this speed 4 ~ 5 times, reading images carries out comprehensive interpretation, and through m test, the best resolution image of final acquisition, calculates tested lens focus.The method realizes high-precision detection, and the focal length solving prior art system under test (SUT) is by environmental factor, human factor, technology debugs level, the impact of the errors of principles and reading error etc. factors brings precision low problem.
Accompanying drawing explanation
Fig. 1: structure of the detecting device schematic diagram of the present invention.
Fig. 2: a kind of optical system focal distance detection process flow diagram of the present invention.
In figure: 1, light source, 2, Target Board, 3, parallel light tube, 4, air floating platform, 5, tested camera lens, 6, TDICCD, 7, precise rotating platform.
Embodiment
Below in conjunction with accompanying drawing, the present invention is described in detail.
A kind of optical system focal distance detection of the present invention, utilizes image motion velocity matching principle to detect focal length, namely must ensure that the portable cord speed of the moving target of infinite point on focal plane is consistent with the portable cord speed of photodetector.If be v as portable cord speed, tested lens focus is f, is angular velocity as the ratio moving linear velocity v and focal distance f
.The focal length of tested camera lens is constant value, so the rotational angular velocity ω of a certain picture point
aonly a corresponding picture moves linear velocity v
a, the portable cord speed of and if only if photodetector moves linear velocity v with picture
atime equal, image definition just can not decline, therefore, and the portable cord speed v of selected photodetector
a, being found out by the method for imaging test can the picture point rotational angular velocity ω of limiting resolution of clear resolved light electric explorer
a, thus calculate the focal length of tested camera lens:
As a kind of special line array CCD (photoelectric coupled device), TDICCD(time delays integral light charge coupled device) carry out the tracking to picture point motion by mobile charge packet in the ranks, row transfer pulse signal often changes one-period T, charge packet just at the displacement D of an in the ranks mobile pixel, then as moving linear velocity
(f
tfrequency for row transfer pulse signal), then 1. formula becomes 2. formula:
In order to realize above-mentioned measuring method, pick-up unit of the present invention, as shown in Figure 1, comprises light source 1, Target Board 2, parallel light tube 3, air floating platform 4, tested camera lens 5, TDICCD6, precise rotating platform 7.
Light source 1 adopts special tungsten light modulation; Target Board 2 adopts standard 4# resolving power test target; Employing 13m focal length model is the parallel light tube 3 of K2497; Employing model is the air floating platform 4 of XZS34; Adopt the TDICCD6 of DALSA company, Pixel Dimensions is 8 μm, and maximum integration progression is 200 grades; Precise rotating platform 7 adopts self-control turntable, turntable speed smoothness 0.00001 °/s.
Comparative selection degree is that the 4# standard resolution chart of 1000:1 is as Target Board 2, this Target Board 2 delineates the striped of different space frequency, each frequency correspond to the striped in 4 groups of pairwise orthogonal directions, Target Board 2 is placed on the focal plane of parallel light tube 3, after parallel light tube 3, the diverging light of Target Board 2 becomes directional light, is equivalent to Target Board 2 and is in infinite point; Parallel light tube 3 to be placed on air floating platform 4 surface vibration isolator; Tested camera lens 5 and TDICCD 6 are placed on precise rotating platform, and tested camera lens 5 is placed on turntable center place, and TDICCD 6 is placed on turntable edge.The mode of operation of TDICCD 6 is for carry out multiexposure, multiple exposure to a target, namely to same target repeatedly imaging charge packet add up, according to the focal length of tested camera lens 5, the focal length of choose reasonable parallel light tube 3, make the spatial frequency of the width of fringe of a certain group of Target Board 2 imaging and TDICCD 6 pixel on focal plane and PHASE DISTRIBUTION identical, namely each pixel line width is identical with one corresponding on Target Board 2 width that is bright or dark fringe imaging, the distance as the pixel that often moves up in TDI side of Target Board 2, row transfer pulse signal drives the charge packet of the every a line of TDICCD 6 simultaneously along TDI direction translation pixel, make two pixels of adjacent lines before and after picture is mobile all to same point imaging, like this after n movement, obtain the image after to n the exposure of same target, if in n moving process, image motion velocity all mates with row transfer pulse signal frequency, clear picture and undamped, after this n time superposition, the formula root mean square of focal length precision that 2. method is surveyed can improve
doubly.
Connect TDICCD 6 power supply, utilize computing machine to be configured TDICCD 6, determine the driving frequency f of the capable transfer pulse signal of TDICCD6
t, operation turning table control case drives turntable 7 steadily to rotate from reference position, and stop motion during arrival end position, utilizes computer recording image.
As shown in Figure 2, a kind of optical system focal distance detection of the present invention, concrete steps are as follows:
Step one, select the light source 1 of brightness uniformity and contrast to be 1000:1 4# standard resolution chart as Target Board 2, Target Board 2 is carved with the grating fringe of 25 groups of different space frequency, Moire fringe is formed after the light therethrough Target Board 2 that light source 1 sends, after being placed on the parallel light tube 3 on air floating platform 4, the diverging light of Target Board 2 is become directional light, for tested camera lens 5, Target Board becomes infinite point target, after tested camera lens 5, Target Board is imaged on the focal plane of tested camera lens 5;
On the precise rotating platform 7 that step 2, the TDICCD 6 being 8 μm by tested camera lens 5 and Pixel Dimensions are placed on, tested camera lens 5 is placed on precise rotating platform 7 center, TDICCD 6 places the edge of precise rotating platform 7, and overlap with the focal plane of tested camera lens 5, connect TDICCD 6 power supply, utilize computing machine to be configured TDICCD 6, determine the driving frequency f of TDICCD 6 row transfer pulse signal
t, move linear velocity, row transfer pulse signal driving frequency f from picture
tthe proportional relation of linear velocity v is moved with picture,
According to formula
1.,
2. with the bigness scale focal length of tested camera lens
with error range Δ f, estimate the range of speeds of precise rotating platform
;
Step 3, in the range of speeds of precise rotating platform 7 set a velocity amplitude, turntable controller inputs precise rotating platform 7 and rotates reference position, end position and velocity amplitude, precise rotating platform 7 is driven steadily to rotate from reference position, stop motion during arrival end position, and correcting action, when computing machine control TDICCD 6 rotates from reference position, send row transfer pulse signal, and start to record image, when arriving end position, stop record image and send row transfer pulse signal;
Step 4, drive precise rotating platform with the speed set in step 3, take pictures from reference position steadily rotates, stop taking pictures when arriving end position, and correcting action, record image, this process repeats 4 ~ 5 times, to obtain 4 ~ 5 width images;
Step 5, reading images carry out comprehensive interpretation, judge whether image exists on TDI direction and differentiate decay, if image being decayed without differentiating on TDI direction, can think that this speed is mated with line frequency, 2. calculating tested lens focus by formula; If image exists larger resolution decay on TDI direction, select speed recruitment according to attenuation degree, repeat step 3 and step 4; Through m test, the best resolution image of final acquisition, calculates tested lens focus.
Claims (1)
1. an optical system focal distance detection, is characterized in that, comprises the following steps:
Step one, select the light source (1) of brightness uniformity, 4# standard resolution chart that contrast is 1000:1 is as Target Board (2), Target Board (2) is carved with the grating fringe of 25 groups of different space frequency, the light therethrough Target Board (2) that light source (1) sends forms Moire fringe afterwards, Moire fringe is after being placed on the parallel light tube (3) on air floating platform (4), the diverging light of Target Board (2) is become directional light, directional light is by after tested camera lens (5), and Target Board (2) is imaged on the focal plane of tested camera lens (5);
On step 2, precise rotating platform (7) that tested camera lens and TDICCD (6) are placed on, tested camera lens (5) is placed on precise rotating platform (7) center, TDICCD (6) places the edge of precise rotating platform (7), and overlap with the focal plane of tested camera lens (5), connect TDICCD (6) power supply, utilize computing machine to be configured TDICCD (6), determine the driving frequency f of TDICCD (6) row transfer pulse signal
t, move linear velocity, row transfer pulse signal driving frequency f from picture
tthe proportional relation of linear velocity v is moved with picture,
According to formula
1.,
2. with the bigness scale focal length of tested camera lens
with error range Δ f, estimate the range of speeds of precise rotating platform (7)
wherein, D represents the displacement of charge packet in an in the ranks mobile pixel;
Step 3, in the range of speeds of precise rotating platform (7) set a velocity amplitude, turntable controller inputs precise rotating platform (7) and rotates reference position, end position and velocity amplitude, precise rotating platform (7) is driven steadily to rotate from reference position, stop motion during arrival end position, and correcting action, when computing machine control TDICCD (6) rotates from reference position, send row transfer pulse signal, and start to record image, when arriving end position, stop record image and send row transfer pulse signal;
Step 4, drive precise rotating platform with the speed set in step 3, take pictures from reference position steadily rotates, stop taking pictures when arriving end position, and correcting action, record image, this process repeats 4 ~ 5 times, to obtain 4 ~ 5 width images;
Step 5: reading images carries out comprehensive interpretation, judges whether image exists on TDI direction and differentiates decay, if image being decayed without differentiating on TDI direction, can think that this speed is mated with line frequency, 2. calculating tested lens focus by formula; If image exists larger resolution decay on TDI direction, select speed recruitment according to attenuation degree, repeat step 3 and step 4; Through m test, the best resolution image of final acquisition, calculates tested lens focus.
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| CN103439088B (en) * | 2013-08-19 | 2015-09-30 | 江苏大学 | The method and apparatus of directional light is produced with convex lens |
| CN103792069B (en) * | 2014-01-14 | 2016-02-10 | 中国空间技术研究院 | A kind of optical imaging system focal length accurate measurement method based on moon imaging |
| CN104748850A (en) * | 2015-03-05 | 2015-07-01 | 青岛市光电工程技术研究院 | Fast assembling and regulating method for spectral imager |
| CN105203304B (en) * | 2015-10-09 | 2018-11-02 | 茂莱（南京）仪器有限公司 | Magnifying power method surveys the optical bench of focal length |
| CN106843303B (en) * | 2016-12-09 | 2023-05-23 | 河南中光学集团有限公司 | Automatic control system and control method for speed of self-adaptive lens view field turntable |
| CN115442530B (en) * | 2022-09-02 | 2023-09-19 | 北京高普乐光电科技股份公司 | Linkage method and device for camera field angle and turntable rotating speed |
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