Method and apparatus for measuring cofocal combined ultra-long focal distance

A measurement method and a technology of a measurement device, which are applied in the direction of testing optical properties, etc., can solve problems such as ultra-long focal length fixed focus that have not yet been seen, and achieve the effects of reducing the length of the measurement optical path, reducing the impact, and high stability

Inactive Publication Date: 2009-04-15
BEIJING INSTITUTE OF TECHNOLOGYGY
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Problems solved by technology

So far, there have been no reports on the direct applicatio...
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Method used

In this embodiment, also work together by focal depth compression optical system 1 and confocal fixed focus system 10, use pupil filter technology to compress the focal depth after reference lens 5 and measured lens 3 and reference lens 5 are combined, improve fixed focus Focus sensitivity.
[0035] The basic idea of ​​...
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Abstract

The invention belongs to the technical field of optical precision measurement, and relates to a method for measuring super long focal length of a confocal combination lens and a device thereof. The method is as follows: firstly determining the focal position of a reference lens and the focal position of the combination of the measured lens and the reference lens according to the confocal focusing principle, measuring the distance delta between the two focal points and the distance d0 between the two lenses, and substituting the delta and the d0 into a formula to calculate the focal length value of the measured lens, a pupil filtering technique can also be used in the measurement to enhance the sensitivity of focal length measurement. The invention proposes that accurate focusing is realized by the characteristics that an object corresponds to the microscope objective focus when the confocal point responds to the maximum curve value, and extends the confocal microscopy principle to the super long focal length measurement field, and proposes the confocal focusing principle. The method combines the confocal focusing principle with the combination lens method, has the advantages of high measurement precision and strong anti-environment interference ability, and can be used for high-precision focal length measurement during the detection and assembly of the super-long focal length lens.

Application Domain

Technology Topic

PhysicsFocal position +6

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  • Method and apparatus for measuring cofocal combined ultra-long focal distance
  • Method and apparatus for measuring cofocal combined ultra-long focal distance
  • Method and apparatus for measuring cofocal combined ultra-long focal distance

Examples

  • Experimental program(1)

Example Embodiment

[0036] Example
[0037] Such as image 3 As shown, a confocal combined ultra-long focal length measurement method, the measurement steps are:
[0038] First, turn on the light source 12, and emit parallel light through the beam splitting system composed of the polarizing beam splitter 13 and the quarter wave plate 14. The reference lens 5 with a focal length of 3000mm is condensed at the focal point a7, and the light is reflected by the mirror 8. , Reflected by the quarter-wave plate 14 and the polarization beam splitter 13 into the confocal fixed-focus system; the condenser 21 in the confocal fixed-focus system condenses the light, and the condensed light passes through the pinhole 20 to illuminate the CCD detector 19; 8 Scan and move along the translation stage a15 in the direction of the optical axis of the reference lens 5. The confocal fixed focus system determines the corresponding focal position a7 of the reference lens by detecting the maximum point of the response signal of the CCD detector 19, and the response signal is as Figure 4 Shown.
[0039] Then, the tested lens 3 is placed between the quarter wave plate 14 and the reference lens 5, and is coaxial with the reference lens 5, again using the confocal fixed focus system, so that the mirror 8 is placed on the reference lens along the translation stage a15 5 Scanning movement in the direction of the optical axis, by detecting the maximum point of the response signal to determine the new focus position b9 caused by the insertion of the tested lens 4;
[0040] Then, the grating length measuring mechanism in the translation stage a15 drives the mirror 8 to move in the direction of the optical axis of the reference lens 5. During the movement of the mirror 8, the translation stage a15 uses the grating length measuring mechanism to measure the focus position a7 and the focus position b9. The distance between Δ6;
[0041] Then, put the gauge block 16 into the optical path so that the planes on both sides are perpendicular to the optical axis of the reference lens 5. The translation stage b18 drives the gauge block 16 to move axially through the connecting rod 17, and touches the reference lens 5 and the tested lens 3 respectively. . The distance moved by the gauge block 16 in the process of touching the lens surface plus the thickness of the gauge block 16 to calculate the surface distance d between the tested lens 3 and the reference lens 5 0 4;
[0042] Then, calculate the principal plane distance d between the tested lens 3 and the reference lens 5 by the following formula:
[0043] d = d 0 + r 12 b 1 n 1 ( r 12 - r 11 ) + ( n 1 - 1 ) b 1 - r 21 b 2 n 2 ( r 22 - r 21 ) + ( n 2 - 1 ) b 2 - - - ( 1 )
[0044] The known parameters in the formula include the thickness b of the tested lens 3 1, Refractive index n 1 , Radius of curvature r 11 , R 12 , The focal length f of the reference lens 5 2 ′, thickness b 2 , Refractive index n 2 , Radius of curvature r 21 , R 22.
[0045] Finally, calculate the focal length of the tested lens 3 by the following formula:
[0046] f 1 ′ = 1 - d f 2 ′ + d f 2 ′ - Δ 1 f 2 ′ - Δ - 1 f 2 ′ - - - ( 2 )
[0047] In this embodiment, the focal depth compression optical system 1 and the confocal fixed focus system 10 work together, and the pupil filter technology is used to compress the focal depth of the reference lens 5 and the combination of the tested lens 3 and the reference lens 5 to improve the focus sensitivity.
[0048] Such as image 3 As shown, a confocal combined lens ultra-long focal length measuring device includes a light source 12, a polarization beam splitter 13, a quarter-wave plate 14, a reference lens 5 and a mirror 8, which are sequentially placed in the light source 12 to emit parallel light rays. It includes a confocal fixed-focus system placed in the reflection direction of the polarizing beam splitter 13, wherein the mirror 8, the polarizing beam splitter 13, and the quarter wave plate 14 reflect the light beam to the confocal fixed-focus system, and the light in the confocal fixed-focus system is sequentially Through the condenser lens 21, the pinhole a20, and illuminate the CCD detector 19; the reflector 8 is placed on the translation stage a15, and cooperates with the confocal fixed focus system to realize the fixed focus of the focus position a7 and the focus position b9.
[0049] The gauge block 16 is connected to the translation stage b18 through the connecting rod 17, and is used to measure the surface distance d between the tested lens 3 and the reference lens 5 0 4;
[0050] The device includes a focal depth compression optical system 1 as a pupil filter for reducing the focal depth of the reference lens 5 and the combination of the tested lens 3 and the reference lens 5.
[0051] The device includes a modulation control system 11, which is used to control the light source 12 and the confocal fixed focus system 10 to perform modulation and filtering to suppress the influence of environmental interference on the measurement accuracy.
[0052] When the distance d 0 =500mm, the focal length f of the reference lens 8 2 ’=3000mm, the measured focal length f 1 When ≈30000mm, the focal length measurement error is ±4.2mm, and the relative measurement error is:
[0053] δf = δ f 1 f 1 = ± 4.2 30000 × 100 % ≈ ± 0.014 %
[0054] This embodiment implements a series of measures to achieve high-precision measurement of an ultra-long focal length, and realizes a confocal combined ultra-long focal length measurement method and device, which has higher measurement accuracy than conventional measurement methods.
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