CN102636181A - Method for detecting focal length of high-precision spatial aerial camera - Google Patents

Abstract

A method for detecting the focal length of a high-precision spatial aerial camera relates to the field of detection of optical-electro-mechanical equipment and solves the problem that an existing method for detecting the focal length of a spatial camera causes light tube image surface errors, reticle line witch errors and secondary reading errors due to factor amplification. An interferometer is used for detecting the optimal image surface position of a detected camera, a reticle is placed at the optimal image surface position of the detected camera, a theodolite loaded with an additional objective lens is used for measuring the included angle of the additional objective lens corresponding to a standard scale value of the reticle at an exit pupil position of the detected camera, and the focal length of the detected spatial camera is obtained. Detecting accuracy and detecting efficiency of the focal length of the camera are effectively improved, and the method is widely applied to the field of detection of optical-electro-mechanical equipment.

Description

Detect the take photo by plane method of camera focus of high precision space

Technical field

The present invention relates to ray machine electricity Equipment Inspection field, be specifically related to a kind of take photo by plane method of camera focus of high precision space that detects.

Background technology

At present, known space camera requires ground scenery size, position are measured, and can handle through the TDI/CCD image and realize.But preceding making demands accurately measured the focal length value of space camera optical system.

It is the enlargement ratio method that the space camera focal length detects the most frequently used method, and its computing formula commonly used is expressed as with formula one:

formula one

In the above-mentioned formula: f _LightFor detecting the focal length of light pipe, X _LightFor detecting the actual scale value of glass sieve plate of light pipe, f _EmptyBe the focal length of space camera to be detected, X _EmptyThe scale value that records for space camera image planes to be detected; In conjunction with Fig. 1, the measuring method of concrete enlargement ratio method is:

A, at first use Abbe horizontal metroscope (being used to detect a kind of instrument of length) accurately to measure the actual scale value X of glass sieve plate _Light, with the focal distance f of transit angle-measuring method detection light pipe _Light

B, glass sieve plate are placed on the image planes place of detecting light pipe, make the detection light pipe send parallel rays;

C, through space camera on the focal plane of picture side, measure the scale value X that seized space camera image planes record with microscope _Empty

The error analysis of the measuring method of enlargement ratio method: one, the focal distance f of error main source parallel light tube _LightAccuracy; The wide uncertainty of glass sieve plate groove of parallel light tube; Twice reading of measuring microscope is not repeated; The accuracy of the lateral magnification β of measuring microscope; Two, magnification method measurement space camera is represented with σ f/f, and wherein, σ f is the focal length measurement value, and f is known focal length value.Error≤1%;

According to above-mentioned analysis, the enlargement ratio method can be introduced a lot of unnecessary errors, like light pipe image planes site error, graticule linewidth error and rereading error.So the focal length to detecting the high precision space camera can bring very big error.

Summary of the invention

The present invention can introduce the problem of light pipe image planes site error, graticule linewidth error and rereading error for the focal distance detecting method that solves the existing space camera adopts the enlargement ratio method, and a kind of take photo by plane method of camera focus of high precision space that detects is provided.

Detect the take photo by plane method of camera focus of high precision space, this method is realized by following steps:

Step 1, the best image planes position of adopting interferometer measurement camera to be detected;

Step 2, on the best image planes position of the camera to be detected that step 1 is measured, place glass sieve plate; Adopt the angle of the transit of the additional object lens of loading, obtain the focal length of space camera to be detected at the corresponding additional object lens of the line width values of the exit pupil position of camera to be detected measurement glass sieve plate;

The focal distance f of said space camera to be detected _EmptyPass through formula

Obtain;

In the above-mentioned formula, y is the line width values of glass sieve plate, and ω is the angle of the corresponding additional object lens of line width values of glass sieve plate.

Principle of work of the present invention: the present invention improves original in the space camera focal distance detecting method; Under original technical conditions; With interferometer space camera is carried out guestimate camera position of focal plane in advance, re-use the Lycra transit and additional object lens are accurately measured the focal length of part camera; Adopt the additional accurate angle-measuring method of object lens; On the known focal plane accurately of detected space camera, place glass sieve plate of known live width; Its line width is 2y; Measure subtended angle 2 ω of the corresponding object lens of line width values, the then focal distance f of space camera to be detected in space camera to be detected exit pupil position in order to load the Lycra transit that adds object lens _EmptyUse formula two tabular forms to be:

formula two

In the above-mentioned formula, y is glass sieve plate live width, and ω is the angle of the relative object lens of glass sieve plate live width;

Owing to adopt the additional error amount of the accurate angle-measuring method of object lens own just less than the enlargement ratio method; The present invention is on the basis of the additional accurate angle-measuring method of object lens; Use additional object lens (n times of beam expander) and the mode that the Lycra transit combines, making camera focus is 2 to 3 times of combined focal length.Increase the focal length of transit in theory, made measuring error be reduced once more.Thereby make space camera when measuring real image, can reduce the distortion of image.

In order to discuss the feasibility of technique scheme, will analyze the uncertainty of the line width values of the relative error of space camera and Bo Luo plate, can prove that finally it is to improve a lot than amplifying method that camera focus of the present invention detects.The relative error of the focal length of space camera is expressed as with formula three:

$\frac{{\mathrm{\σ\; f}}^{\′}}{f}=\±\sqrt{{\left(\frac{\mathrm{\σ\; y}}{y}\right)}^2+{\left(\frac{2}{\mathrm{Sin}2w}\right)}^2{\mathrm{\σ\; w}}^2}$ Formula three

Can find out that by formula three for long as far as possible littler apart from space camera 2 ω angles, the uncertainty of sin2 ω ≈ 2 ω line widths is expressed as with formula four:

$\frac{{\mathrm{\σ\; y}}^{\′}}{f}=\±\sqrt{{\left(\frac{\mathrm{\σ\; y}}{y}\right)}^2{\left(\frac{2}{2w}\right)}^2{\mathrm{\σ\; w}}^2}$ Formula four

Used by formula four explanation to have the uncertainty that 3 times of additional object lens transits record 2 ω angles and be σ 2w=2 " then σ w=1 ", the width uncertainty of σ 2y groove is 0.001mm; σ y=σ 2y/2=0.0005mm;

By above-mentioned analysis, can bring above-mentioned relative error value and uncertainty into formula four, can get formula five

$\frac{{\mathrm{\σ\; y}}^{\′}}{f}=\sqrt{{\left(\frac{0.005}{10}\right)}^2+{\left(\frac{1}{20*60}\right)}^2*1^{\′\′}}$ Formula five

The method has adopted additional object lens, has increased the combined focal length of Lycra optic theodolite optical system, has improved pointing accuracy twice.By formula five explanations, the source of error of the method mainly is made up of the line width error of transit and Bo Luo plate, so the present invention is used to detect the focal length of high precision space camera, obtains well to be superior to other detection methods result.

Beneficial effect of the present invention: the present invention provides a kind of take photo by plane method of camera focus of high precision space that detects, and can reduce the error of focal length measurement, and purpose is in order to obtain the position of image accurately.The inventive method reduces the generation of unnecessary error in the focal length testing process of space camera, improves the camera accuracy of detection as far as possible.With contrasting on the conventional sense precision of camera and the accuracy of detection of the present invention, the present invention effectively improves precision.The present invention significantly improves the focal length accuracy in detection and the detection efficiency of camera, on human and material resources, financial resources, obtains maximum saving and optimized distribution.

Description of drawings

Fig. 1 measures camera focus device synoptic diagram for adopting existing enlargement ratio method;

Fig. 2 is the method for interferometric method phasing machine image planes, and purpose is to obtain to measure the MTF optimum position before the present invention.

Fig. 3 is the method for the measurement space camera focus of the present invention's use,

Among the figure: 1, glass sieve plate, 2, detect parallel light tube, 3, space camera to be detected, 4, space camera focal plane to be detected, 5, microscope, 6, interferometer, 7, plane mirror, 8, transit, 9, additional object lens.

Embodiment

In conjunction with Fig. 2 and Fig. 3 this embodiment is described; Detect the take photo by plane method of camera focus of high precision space, realize that the basic tool of this method is: Lycra transit, model are 5100 types; Glass sieve plate, the line width values of said glass sieve plate (standard scale value) is respectively: 2mm, 4mm, 10mm or 20mm; Additional object lens, additional object lens are 3 times of beam expanders, require to use with the combination of Lycra transit, the combined focal length minimum should be a space camera focal length 1/2nd to 1/5th, zygo interferometer, model JPI-HR, sextuple adjustment rack;

Concrete detection method is: the best image planes position of, adopting interferometer measurement camera to be detected;

Because the space camera relative aperture is generally all greater than 1/10, depth of focus is bigger relatively, and in order to improve the ability that it differentiates ground object, so improve the axial MTF transfer function values of optical system, could improve the image quality of camera; In conjunction with Fig. 2, adopt the method for interferometer measurement phasing camera image planes to be detected,

At first with interferometer 6, space camera to be detected 3, plane mirror 7 be as on the identical platform, starts interferometer 6 then and on said interferometer 6, install and space camera 3 corresponding camera lenses to be detected;

Adopt the autocollimatic method to find the spherical wave of interferometer 6 emissions once more after optical system arrives the picture that plane mirror returns; Detailed process is: a, interferometer 6 is placed on the axis of space camera 3 to be detected; B, adjustment plane mirror 7 make the picture that returns overlap with the emission picture point; C, glass sieve plate 1 is placed to interferometer 6 focal positions; And, d, axially adjust the position (with the below of sextuple adjustment rack) of interferometer 6 as for interferometer 6 at a little blue ink (the blue wash ink is in order in the work of back, to find image to do homework) of the surface point of glass sieve plate 1, make that going up the spherical aberration value week is zero; Adjust glass sieve plate 1 position simultaneously, make that the image of ink is clear on the CCD of ZGYO interferometer 6 imaging face on glass sieve plate 1.

Two, the measurement of focal length in conjunction with Fig. 3, at first places transit 8, plane mirror 7 and space camera to be detected 3 on the identical platform; Additional object lens 9 should be enclosed within transit 8 camera lens the place aheads; Then, confirm that plane mirror 7 vertical rotation axis should will go here and there on same axis (can be more accurate when making the standard scale value of measuring glass sieve plate) if there is site error need carry out the secondary adjustment with space camera to be detected 3 and transit 8.

At last; With the position of the transit 8 infinite distances standard scale value on glass sieve plate 1 of seeing space camera focal plane to be detected 4 places through plane mirror 7 reflections clearly that is as the criterion; Rotate the live width on the transit 8 transverse axis measuring reticles,, obtain the focal length of space camera to be detected through computing formula two.

Claims (4)

1. detect the take photo by plane method of camera focus of high precision space, it is characterized in that this method is realized by following steps:

Step 1, employing interferometer (6) are measured the best image planes position of camera to be detected (3);

Step 2, on the best image planes position of the camera to be detected (3) that step 1 is measured, place glass sieve plate (1); Adopt the angle of the transit (8) of the additional object lens (9) of loading, obtain the focal length of space camera to be detected (3) at the corresponding additional object lens (9) of the line width values of exit pupil position measurement glass sieve plate (1) of camera to be detected (3);

The focal distance f of said space camera to be detected (3) _EmptyPass through formula

Obtain;

In the above-mentioned formula, y is the line width values of glass sieve plate, and ω is the angle of the corresponding additional object lens (9) of line width values of glass sieve plate.

2. the take photo by plane method of camera focus of detection high precision according to claim 1 space is characterized in that described additional object lens (9) are 3 to 5 times of beam expanders;

3. the take photo by plane method of camera focus of detection high precision according to claim 1 space is characterized in that described transit (8) is the Lycra transit of 5100 types.

4. the take photo by plane method of camera focus of detection high precision according to claim 1 space is characterized in that the line width values of said glass sieve plate (1) is respectively 2mm, 4mm, 10mm or 20mm.

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