U.S. patent application number 12/327521 was filed with the patent office on 2009-11-12 for system and method for measuring length of camera lens.
This patent application is currently assigned to HON HAI PRECISION INDUSTRY CO., LTD.. Invention is credited to KUN-JUNG TSAI.
Application Number | 20090279075 12/327521 |
Document ID | / |
Family ID | 41211104 |
Filed Date | 2009-11-12 |
United States Patent
Application |
20090279075 |
Kind Code |
A1 |
TSAI; KUN-JUNG |
November 12, 2009 |
SYSTEM AND METHOD FOR MEASURING LENGTH OF CAMERA LENS
Abstract
A system for measuring a total track length of a telescopic lens
includes a testing chart, a light source, a processor, a display
screen and a range finder. The lens and an image sensor are
received in a holder. The testing chart has a frame pattern and a
plurality of line pair patterns. The testing chart faces and aligns
with the image sensor for allowing the image sensor to capture an
image of the testing chart. The processor analyzes the image
generated by the image sensor, so as to obtain a modulation
transfer function value representative of a precision focal
position of the lens. The range finder measures a first distance
between the image sensor and the range finder, a second distance
between the lens and the range finder, and calculates a distance
difference between the first and second distances to obtain the
total track length of the lens.
Inventors: |
TSAI; KUN-JUNG; (Tu-Cheng,
TW) |
Correspondence
Address: |
PCE INDUSTRY, INC.;ATT. Steven Reiss
288 SOUTH MAYO AVENUE
CITY OF INDUSTRY
CA
91789
US
|
Assignee: |
HON HAI PRECISION INDUSTRY CO.,
LTD.
Tu-Cheng
TW
|
Family ID: |
41211104 |
Appl. No.: |
12/327521 |
Filed: |
December 3, 2008 |
Current U.S.
Class: |
356/124 |
Current CPC
Class: |
G01M 11/0214 20130101;
G01M 11/0257 20130101; G03B 43/00 20130101 |
Class at
Publication: |
356/124 |
International
Class: |
G01M 11/08 20060101
G01M011/08 |
Foreign Application Data
Date |
Code |
Application Number |
May 6, 2008 |
CN |
200810301431.6 |
Claims
1. A system for measuring a total track length of a telescopic
lens, the telescopic lens and an image sensor received in a holder,
the telescopic lens being movable relative to the image sensor, the
system comprising: a testing chart having a frame pattern and a
plurality of line pair patterns arranged in the frame pattern, each
of the line pair patterns including a plurality of black and white
line pairs, the testing chart facing the holder; a light source for
illuminating the testing chart; the testing chart being configured
for facing and aligning with the image sensor for allowing the
image sensor to capture an image of the line pair patterns of the
testing chart; a processor configured for analyzing the line pair
patterns of the testing chart of the image generated by the image
sensor, so as to obtain a modulation transfer function value
representative of a precision focal position of the lens; a display
screen configured for displaying the image generated by the image
sensor and the modulation transfer function value thereon; and a
range finder configured for measuring a first distance between the
image sensor and the range finder, a second distance between the
lens and the range finder, and calculating a distance difference
between the first distance and the second distance to obtain the
total track length of the lens.
2. The system as described in claim 1, wherein a distance between
the testing chart and the camera module is substantially equal to a
minimum focus distance of the lens.
3. The system as described in claim 1, wherein the range finder
comprises an emitting and receiving unit, the emitting and
receiving unit configured for emitting a laser beam to a sensing
surface of the image sensor and receiving the laser beam reflected
by the image sensor, so as to obtain the first distance
therebetween, the emitting and receiving unit configured for
emitting another laser beam to an exterior surface of the lens and
receiving the laser light reflected by the lens, so as to obtain
the second distance therebetween.
4. The system as described in claim 1, wherein at least two of the
line pair patterns are different from each other in spatial
frequency.
5. The system as described in claim 1, wherein the line pairs of
adjacent line pair patterns are perpendicular to each other.
6. A method for measuring a total track length of a telescopic
lens, comprising: providing a testing chart, the testing chart
having a frame pattern and a plurality of line pair patterns
arranged in the frame pattern, each of the line pair patterns
including a plurality of black and white line pairs; aligning the
image sensor with the frame pattern of the testing chart; providing
a range finder; measuring a first distance between the image sensor
and the range finder using the range finder; mounting a lens into
the holder, the lens disposed between the image sensor and the
testing chart; analyzing an image of the line pair patterns of the
testing chart while adjusting a distance between the lens and the
image sensor, so as to cause the lens focusing on a precision focal
position; measuring a second distance between the lens and the
range finder using the range finder; calculating a distance
difference between the first distance and the second distance, so
as to obtain the total track length of the lens, and displaying the
total track length of the lens to a user.
7. The method as described in claim 6, wherein the frame pattern is
highlighted relative to the line pair patterns.
8. The method as described in claim 6, further comprising
determining whether the frame pattern in the image of the testing
chart is centrosymmetric about a center of the image sensing area
of the image sensor, after mounting the lens into the holder, if
not, moving the lens until the frame pattern in the image of the
testing chart is centrosymmetric about the center of the image
sensing area of the image sensor.
9. The method as described in claim 6, wherein a distance between
the lens and the testing chart is substantially equal to a minimum
focus distance of the lens.
10. The method as described in claim 9, further comprising
analyzing the image of the testing chart from the image sensor, so
as to obtain a modulation transfer function value representative of
a precision focal position of the lens.
11. The method as described in claim 10, further comprising
displaying the image of the testing chart from the image sensor and
the modulation transfer function value from the processor
thereon.
12. The method as described in claim 6, wherein at least two of the
line pair patterns are different from each other in spatial
frequency.
13. The method as described in claim 6, wherein the line pairs of
adjacent line pair patterns are perpendicular to each other.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] Relevant subject matter is disclosed in co-pending U.S.
patent application Ser. No. 12/170,761 filed on Jul. 7, 2008 and
entitled "SYSTEM AND METHOD FOR MEASURING OPTICAL RESOLUTION OF
LENS". The co-pending U.S. patent application is assigned to the
same assignee as the instant application. The disclosure of the
above-identified co-pending application is incorporated herein by
reference.
BACKGROUND
[0002] 1. Technical Field
[0003] This disclosure relates to camera lens length measuring
systems, and particularly to a system and a method for measuring a
total track length of a telescopic camera lens.
[0004] 2. Description of Related Art
[0005] Camera modules are generally installed in mobile telephones,
personal digital assistants or other portable electronic
apparatuses to record memorable moments due to their convenience
and practicality. The designs of the portable electronic
apparatuses have evolved toward lightweight and compactness
tendency, so have the currently popular digital camera modules.
[0006] The digital camera module generally includes a lens, a
sensor for converting light transmitted through the lens into
electronic image signals, and a motor for driving the lens into
telescopic movement. Most portable electronic apparatuses equipped
with camera modules have a limited internal space, in such a
condition, a total track length (a distance between a first surface
of the lens and a film surface of the sensor) of the lens need to
be relatively short. However, the short total track length of the
lens makes it difficult for the camera module to achieve a high
optical performance while being compact, especially during the
telescopic movement of the lens.
[0007] What is needed, therefore, is a system and method for
measuring a total track length a lens, which is capable of
identifying whether the camera module with the lens is suitable for
the portable electronic apparatuses while maintaining a high
optical performance.
SUMMARY
[0008] A system for measuring a total track length of a telescopic
lens is provided. The telescopic lens and an image sensor are
received in a holder. The telescopic lens is movable relative to
the image sensor. The system includes a testing chart, a light
source, a processor, a display screen and a range finder. The
testing chart has a frame pattern and a plurality of line pair
patterns arranged in the frame pattern. Each of the line pair
patterns includes a plurality of black and white line pairs. The
testing chart faces the holder. The light source is for
illuminating the testing chart. The testing chart is configured for
facing and aligning with the image sensor for allowing the image
sensor to capture an image of the line pair patterns of the testing
chart. The processor is configured for analyzing the line pair
patterns of the testing chart of the image generated by the image
sensor, so as to obtain a modulation transfer function value
representative of a precision focal position of the lens. The
display screen is configured for displaying the image generated by
the image sensor and the modulation transfer function value
thereon. The range finder is configured for measuring a first
distance between the image sensor and the range finder, a second
distance between the lens and the range finder, and calculating a
distance difference between the first distance and the second
distance to obtain the total track length of the lens.
[0009] Other advantages and novel features of the present system
will become more apparent from the following detailed description
of embodiment when taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Many aspects of the system and method can be better
understood with reference to the following drawings. The components
in the drawings are not necessarily drawn to scale, the emphasis
instead being placed upon clearly illustrating the principles of
the present system and method. Moreover, in the drawings, like
reference numerals designate corresponding parts throughout the
several views.
[0011] FIG. 1 is a schematic view of a system for measuring a total
track length of a lens in accordance with a first step of an
exemplary embodiment.
[0012] FIG. 2 is a schematic view of the system for measuring the
total track length of the lens in accordance with a second step of
the exemplary embodiment.
[0013] FIG. 3 is a top plane view of a testing chart of the
measuring system of FIG. 1.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0014] Referring to FIG. 1 and FIG. 2, an exemplary system 100 for
measuring a total track length of a lens is provided. The system
100 includes a camera module 10, a testing chart 20, a light source
21, a range finder 30 and a computer 40.
[0015] The camera module 10 includes a holder 12, an image sensor
14 and a lens system 16. A receiving space 120 is defined in a
central portion of the holder 12 for receiving the image sensor 14
and the lens system 16 therein. An opening 121 is defined in a top
end of the holder 12. A plurality of first screw threads is formed
on an inner surface of the holder 12 adjacent to the opening 121.
The lens system 16 includes a tubular lens barrel 160 and a
substantially cylindrical lens 162. The lens 162 is fixedly
received in the lens barrel 160. The lens barrel 160 includes an
annular sidewall 163 and a top wall 161 extending horizontally and
inwardly from a top end of the sidewall 163. A plurality of second
screw threads corresponding to the first screw threads is formed on
an outer surface of the sidewall 163. The second screw threads are
screwed into the first screw threads for threadingly engaged the
lens system 16 and the holder 12 together. During operation of the
camera module 10, the lens system 16 moves telescopically along an
axial direction of the holder 12. The image sensor 14 is received
in a bottom end of the receiving space 120. The image sensor 14 can
be selected from a charge coupled device (CCD) and a complementary
metal oxide semiconductor transistor (CMOS). The image sensor 14
has an image sensing area (in present embodiment, the entire top
surface of the image sensor 14 is the image sensing area).
[0016] The testing chart 20 is located over the camera module 10
and spaced a distance from the camera module 10. The distance
between the testing chart 20 and the camera module 10 is
substantially the same as a minimum focus distance of the lens 162
of the camera module 10. When the camera module 10 is focused on
the testing chart 20, the lens 162 protrudes out of the holder 12
of the camera module 10 through the opening 121 farthest. In the
present embodiment, the minimum focus distance of the lens 162 is
about 0.6 m (meter).
[0017] Referring to FIG. 3, the testing chart 20 includes a frame
pattern 221 and a plurality of line pair patterns 222, 223, 224
arranged in the frame pattern 221. The frame pattern 221 is
rectangular. In order to achieve a contrasting view of the line
pair patterns 222, 223, 224 for the lens 162 and the image sensor
14, the frame pattern 221 is highlighted relative to the line pair
patterns 222, 223, 224 with a width L in range of 0.5 mm and 2 mm
(millimeter). Each of the line pair patterns 222, 223, 224 includes
a plurality of black and white parallel line pairs. The line pair
patterns 222, 223, 224 are different from each other in spatial
frequency, i.e., the number of the black and white line pairs per
millimeter distance in each of the line pair patterns 222, 223, 224
is different. In areas a, b, and c, each includes four
corresponding line pair patterns 222, 223, 224, and the line pair
of adjacent line pair patterns 222, 223, 224 are perpendicular to
each other. One area 22 is located on a central portion of the
frame pattern 221 and comprised of four areas a. Four areas 23 are
located on four corners of the frame pattern 221, respectively.
Each of the areas 23 is comprised of one area b. Four areas 24 are
located on four sides of the area 22, respectively. Each of the
areas 24 is comprised of two areas c arranged side by side. The
frame pattern 221 and the line pair patterns 222, 223, 224 of the
testing chart 20 faces the lens 160.
[0018] The light source 21 is located over the testing chart 20.
The light source 21 can be a light emitting diode (LED), and is
configured for illuminating the testing chart 20. Light arrived at
the testing chart 20 is reflected by the frame pattern 221 and the
line pair patterns 222, 223, 224 to the lens 160. The reflected
light then passes through the lens 160 to the image sensor 14, and
the image sensor 14 is capable of receiving and converting light
transmitted through the lens 162 into electronic image signals
associated with the frame pattern 221 and the line pair patterns
222, 223, 224.
[0019] The range finder 30 is located between the camera module 10
and the testing chart 20. The range finder 30 includes an
optoelectronic emitting and receiving unit 32 and a calculating
unit 34. During operation of the range finder 30, the emitting and
receiving unit 32 firstly generates a laser light to a first aimed
surface 140, i.e., the top surface of the image sensor 14, and
receives the laser light which is reflected by the first aimed
surface 140, thereby obtaining a distance between the first aimed
surface 140 and the range finder 30. In the same way, the emitting
and receiving unit 32 generates another laser light to a second
aimed surface 168, i.e., a top surface of the top wall 161 of the
lens barrel 160, and receives the laser light which is reflected by
the second aimed surface 168, thereby obtaining a distance between
the second aimed surface 168 and the range finder 30. The
calculating unit 34 calculates a distance difference between the
first aimed surface 140 and the second aimed surface 168, i.e., the
top surface of the image sensor 14 and the top surface of the top
wall 161 of the lens barrel 160, which is a total extendable length
of the lens 162. Accordingly, when the lens 162 protrudes out of
the holder 12 with respective to the image sensor 14, a maximal
total tack length of the lens 162 can be obtained.
[0020] The computer 40 is electrically connected to the image
sensor 14. The computer 40 includes a processor 42 and a display
screen 44. The processor 42 mainly has an analog-to-digital
converter and an optical resolution analyzer therein. The
analog-to-digital converter is configured for converting the
electronic image signals associated with the frame pattern 221 and
the line pair patterns 222, 223, 224 from the image sensor 14,
which are in form of analog image signals, into a form of digital
image signals. The optical resolution analyzer is configured for
analyzing the image signals associated with the line pair patterns
222, 223, 224 from the analog-to-digital converter according to a
Modulation Transfer Function (MTF), for example,
MTF=(I.sub.max-I.sub.min)/(I.sub.max+I.sub.min), with I.sub.max
representing an intensity of the white lines in one of the line
pair patterns 222, 223, 224 or one of the areas 22, 23, 24, and
I.sub.min representing an intensity of the black lines in the same
one of the line pair patterns 222, 223, 224 or the same one of the
areas 22, 23, 24. The optical resolution analyzer can calculate the
MTF value for a number of times, thereby capable of providing an
average MTF value to represent a precision focusing position of the
lens 162.
[0021] The display screen 44 is electrically connected to the
processor 42. During a telescopic movement of the lens 162, the
display screen 44 can displays the image associated with the frame
pattern 221 and the line pair patterns 222, 223, 224 from the image
sensor 14 and the MTF value thereon. When the camera module 10 is
focused on the testing chart 20 which is located on the minimum
focus distance of the lens 162, the average MTF value reaches its
maximum and the lens 162 stops on the focusing position.
Simultaneously, the lens 162 protrudes out of the camera module 10
farthest with respective to the image sensor 14.
[0022] A method for measuring a total track length of the lens 162
using the system 100, is described in the following steps:
[0023] (1) mounting the camera module 10 without the lens system 16
under the testing chart 20, referring to FIG. 1, the image sensor
14 of the camera module 10 being received in the bottom end of the
receiving space 120 of the holder 12 and facing the testing chart
20 via the opening 121 of the holder 12;
[0024] (2) adjusting the camera module 10 to make a central axis of
the image sensing area of the image sensor 14 coaxial with a
central axis of the frame pattern 221 of the testing chart 20;
[0025] (3) disposing the range finder 30 between the testing chart
20 and the camera module 10, the range finder 30 emitting a laser
light to the top surface of the image sensor 14 and receiving the
laser light reflected by the image sensor 14 via the emitting and
receiving unit 32, so as to measure the first distance H between
the top surface of the image sensor 14 and the range finder 30;
[0026] (4) installing the lens system 16 into the camera module 10,
referring to FIG. 2, an optical axis of the lens 162 being aligned
with the central axis of the image sensing area of the image sensor
14;
[0027] (5) adjusting the lens 162 to move telescopically along an
axial direction by analyzing the image associated with the line
pair patterns 222, 223, 224 on the image sensor 14, so as to make
the lens 162 focusing on a precision focal position;
[0028] (6) the range finder 30 emitting another laser light to the
top surface of the top wall 161 of the lens barrel 160 and
receiving the laser light reflected by the top surface of the top
wall 161 via the emitting and receiving unit 32, so as to measure
the second distance h between the top wall 161 and the range finder
30;
[0029] (7) calculating the distance difference between the first
distance H and the second distance h, so as to obtain the total
track length of the lens 162;
[0030] (8) displaying the total track length of the lens 162 to a
user via the display screen 44.
[0031] In step (2), the central axis of the image sensor 14 and the
central axis of the frame pattern 221 can be easily defined by
geometry. In step (4), since the image associated with the frame
pattern 221 and the line pair patterns 222, 223, 224 is displayed
on the display screen 44 via the image sensor 14, it is easy to
determine whether the central axis of the image sensing area of the
image sensor 14 is align with that of the frame pattern 221 of the
testing chart 20 by moving the camera module 10 until the image
associated with the frame pattern 221 is centrosymmetric about a
center line of the display screen 44. In steps (5) and (6), the
lens 162 and the image sensor 14 can capture the image associated
with all of the line pair patterns 222, 223, 224 therein, or
capture images associated with the respective line pair patterns
222, 223, 224, and the processor 42 can process the respective
images and thus obtain a modulation transfer function value
representative of a precision focal position of the lens 162. On
this precision focusing position, the lens 162 protrudes out of the
holder 12 farthest respective to the image sensor 14, thus, the
maximal total track length of the lens 162 is obtained.
[0032] It is understood that the above-described embodiments are
intended to illustrate rather than limit the invention. Variations
may be made to the embodiments and methods without departing from
the spirit of the invention. Accordingly, it is appropriate that
the appended claims be construed broadly and in a manner consistent
with the scope of the invention.
* * * * *