Digital Camera Patent Abstract
An optical probe apparatus for determining a position of an image
sensor in a digital camera relative to a reference surface on the
digital camera. The optical probe assembly includes a probe mounting
surface adapted to be removably mountable to the digital camera
and lockable in a predetermined orientation relative to the reference
surface of the digital camera; an angle cleaved optical fiber emitting
a beam of light; a lens disposed in the path of the beam of light
and directing the beam of light along an axis normal to a plane
of the lens toward the object; and a mounting member supporting
the optical fiber such that the beam of light is directed along
an axis normal to the plane of the lens and directed to the center
of the lens. An optically transparent material (such as a pellicle
or glass plate) is disposed intermediate the probe mounting surface
and image sensor. Digital Camera Patent Claims
What is claimed is:
1. An optical probe apparatus for determining a position of an
object in a digital camera relative to a reference surface on the
digital camera, the optical probe assembly comprising:
a probe mounting surface adapted to be removably mountable to the
digital camera and lockable in a predetermined orientation relative
to the reference surface on the digital camera;
an angle cleaved optical fiber emitting a beam of light;
a lens disposed in the path of the beam of light and directing
the beam of light along an axis normal to a plane of the lens toward
the object;
a mounting member supporting the optical fiber such that the beam
of light is directed along an axis normal to the plane of the lens
and directed to the center of the lens; and
an optically transparent material disposed intermediate the probe
mounting surface and the object.
2. The optical probe apparatus according to claim 1 wherein the
optically transparent material is a pellicle.
3. The optical probe apparatus according to claim 2 wherein the
pellicle is comprised of a polyester film material having a thickness
of approximately 1-3 .mu.m.
4. The optical probe apparatus according to claim 1 wherein the
optically transparent material is a glass plate.
5. The optical probe apparatus according to claim 4 wherein the
glass plate having a thickness of approximately 4-7 mm.
6. The optical probe apparatus according to claim 1 wherein the
mounting member includes a fiber receptacle and an angled plate.
7. The optical probe assembly according to claim 1 wherein the
mounting member includes a chuck.
8. The optical probe assembly according to claim 7 wherein the
mounting member further includes a ferrule.
9. The optical probe assembly according to claim 7 wherein the
mounting member further includes at least one opening in which the
chuck is disposed.
10. The optical probe assembly according to claim 1 wherein the
lens is a GRIN lens.
11. The optical probe assembly according to claim 1 further comprising
a fiber strain relief.
12. An optical probe apparatus for measuring a physical distance
between a reference surface on a digital camera and an object disposed
within the digital camera, the optical probe assembly comprising:
a probe mounting surface adapted to be removably mountable to the
digital camera and lockable at a predetermined distance from and
in a predetermined orientation relative to the reference surface
of the digital camera;
an angle cleaved optical fiber oriented to emit a beam of light
along an axis normal to the reference surface toward the object;
and
a lens disposed in the path of the beam of light and directing
the beam of light along an axis normal to a plane of the lens toward
the object;
a mounting member supporting the optical fiber and the lens such
that the beam of light is directed along an axis normal to the plane
of the lens and directed to the center of the lens; and
an optically transparent material disposed intermediate the probe
mounting surface and the object.
13. The optical probe apparatus according to claim 12 wherein the
optically transparent material is a pellicle.
14. The optical probe apparatus according to claim 13 wherein the
pellicle is comprised of a polyester film material having a thickness
of approximately 1-3 .mu.m.
15. The optical probe apparatus according to claim 12 wherein the
optically transparent material is a glass plate.
16. The optical probe apparatus according to claim 15 wherein the
glass plate having a thickness of approximately 4-7 mm.
17. The optical probe assembly according to claim 12 wherein the
mounting member includes a chuck.
18. The optical probe assembly according to claim 17 wherein the
mounting member further includes a ferrule.
19. An apparatus for determining a position of an image sensor
in a digital camera relative to a reference surface on the digital
camera, the apparatus comprising:
an optical probe assembly comprising:
(a) a probe mounting surface adapted to be removably mountable
to the digital camera and lockable in a predetermined orientation
relative to the reference surface on the digital camera;
(b) an angle cleaved optical fiber emitting a beam of light;
a lens disposed in the path of the beam of light and directing
the beam of light along an axis normal to a plane of the lens toward
the object;
(c) a mounting member supporting the optical fiber such that the
beam of light is directed along an axis normal to the plane of the
lens and directed to the center of the lens; and
(d) an optically transparent material disposed intermediate the
probe mounting surface and the object; and
a non-coherent light source optically coupled to the optical probe
assembly;
a non-coherent light interferometer optically coupled to the optical
probe assembly; and
a computer in electrical association with the non-coherent light
interferometer.
20. The optical probe apparatus according to claim 19 wherein the
optically transparent material is a glass plate, the optical path
through the glass plate being larger than a maximum scan distance
scanned with the non-coherent light interferometer.
Digital Camera Patent Description
FIELD OF THE INVENTION
The present invention relates generally to an optical probe, particularly
an optical probe for use in determining a position of an image sensor
in a digital camera, whereby the image sensor can be positioned
to provide a focused image.
BACKGROUND OF THE INVENTION
In a typical digital camera, an image beam is directed through
a lens and onto an imager or image sensor, for example a CCD (Charge
Coupled Device), comprised of an array of sensing elements. The
lens and the CCD need to be properly positioned relative to each
other within the digital camera to provide a focused image. In order
to properly position the CCD, the position of the CCD needs to be
determined. Such a position can be determined relative to a reference
surface or reference plane on the digital camera.
U.S. Pat. No. 5,757,485 (Marcus et al) and U.S. Pat. No. 5,757,486
(Marcus et al), commonly assigned and incorporated herein by reference,
relate to a digital camera image sensor positioning apparatus and
method which includes a non-coherent light interferometer. The apparatus
and method include an optical probe assembly removably mountable
to a digital camera. The non-coherent light interferometer is in
communication with the optical probe assembly to determine a depth
from a reference surface to the image surface and optical probe
assembly. The apparatus and method have been suitable for their
intended purpose, however, certain components of the optical probe
assembly require gentle handling, for example, the pellicle. To
utilize the apparatus and method in a manufacturing environment,
such gentle handling may not be present. Thus, a robust design is
needed. Accordingly, a need continues to exist for an optical probe
assembly which is robust, has a simple construction, can be readily
assembled and aligned, and can be used in a manufacturing environment,
particularly by novice users. Further, a need exists to improve
the angular acceptance cone of the optical probe to enable measurement
of imagers which have a larger degree of tilt with respect to the
ideal plane of the imager.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a robust optical
probe assembly which can be used in determining a position of an
image sensor in a digital camera.
Another object of the invention is to provide such a robust optical
probe assembly which is transportable, simple to use, low in cost,
and can be readily mounted to a digital camera.
Yet another object of the invention is to provide such an optical
probe assembly which is easy to manufacture, has a simple construction,
and can be readily assembled and aligned.
Still another object of the invention is to improve the angular
acceptance cone of the optical probe to enable measurement of imagers
tilted with respect to the focal plane.
These objects are given only by way of illustrative example. Thus,
other desirable objectives and advantages inherently achieved by
the disclosed invention may occur or become apparent to those skilled
in the art. The invention is defined by the appended claims.
According to one aspect of the present invention, there is provided
an optical probe apparatus for determining a position of an image
sensor in a digital camera relative to a reference surface on the
digital camera. The optical probe assembly comprises a probe mounting
surface, an angle cleaved optical fiber emitting a beam of light,
a lens, a mounting member, and an optically transparent material.
The probe mounting surface is adapted to be removably mountable
to the digital camera and lockable in a predetermined orientation
relative to the reference surface of the digital camera. The lens
is disposed in the path of the beam of light and directs the beam
of light along an axis normal to a plane of the lens toward the
object. The mounting member supports the optical fiber such that
the beam of light is directed along an axis normal to the plane
of the lens and directed to the center of the lens. The optically
transparent material is disposed intermediate the probe mounting
surface and the image sensor. The optically transparent material
may be a pellicle or a glass plate.
According to another aspect of the present invention, there is
provided an optical probe apparatus for measuring a physical distance
between a reference surface on a digital camera and an object disposed
within the digital camera. The optical probe assembly comprises
a probe mounting surface, an angle cleaved optical fiber oriented
to emit a beam of light along an axis normal to the reference surface
toward the object, a lens, a mounting member, and an optically transparent
material. The probe mounting surface is adapted to be removably
mountable to the digital camera and lockable at a predetermined
distance from and in a predetermined orientation relative to the
reference surface of the digital camera. The lens is disposed in
the path of the beam of light and directs the beam of light along
an axis normal to a plane of the lens toward the object. The mounting
member supports the optical fiber and the lens such that the beam
of light is directed along an axis normal to the plane of the lens
and directed to the center of the lens. The optically transparent
material is disposed intermediate the probe mounting surface and
image sensor. The optically transparent material may be a pellicle
or a glass plate.
The present invention provides an optical probe assembly suitable
for determining the position of an image sensor in a digital camera.
The optical probe assembly is robust, transportable, simple to use,
and reduced in cost.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects, features, and advantages of the
invention will be apparent from the following more particular description
of the preferred embodiments of the invention, as illustrated in
the accompanying drawings.
FIG. 1 shows a lens mounted within a camera body.
FIG. 2 shows a CCD mounted within a camera body.
FIG. 3 shows a non-coherent light interferometric measurement apparatus
according to the present invention.
FIG. 4(a) shows an exploded view of a first embodiment of an optical
probe assembly of FIG. 3 employing a pellicle.
FIG. 4(b) shows a perspective view of the first embodiment of the
optical probe assembly of FIG. 3.
FIG. 4(c) shows an exploded view of the first embodiment of the
optical probe assembly of FIG. 3 employing a transparent material,
such as glass.
FIG. 5 shows a schematic view of an angled optical fiber.
FIG. 6 shows a schematic view of the arrangement of the angled
optical fiber within the optical probe assembly.
FIG. 7(a) shows a schematic view of a mounted angled optical fiber
for use in a second embodiment of an optical probe assembly in accordance
with the present invention.
FIG. 7(b) shows a schematic view of a probe chuck for use with
the second embodiment of the optical probe assembly.
FIG. 7(c) shows an exploded perspective view of the second embodiment
of the optical probe assembly.
FIG. 7(d) shows an exploded perspective view of a portion of the
second embodiment of the optical probe assembly.
FIG. 7(e) shows a perspective view of a portion of the second embodiment
of the optical probe assembly.
FIG. 7(f) shows a perspective view of a portion of the second embodiment
of the optical probe assembly.
FIG. 8 shows a schematic view of the relationship of the optical
probe assembly and the CCD when the optical probe assembly is mounted
to the camera body.
DETAILED DESCRIPTION OF THE INVENTION
The following is a detailed description of the preferred embodiments
of the invention, reference being made to the drawings in which
the same reference numerals identify the same elements of structure
in each of the several figures.
Referring to FIG. 1, a lens 12 is mounted to a camera body 10 by
means of a camera lens mount 14. The distance at which lens 12 focuses
light in the camera body is referred to as the focal depth F.sub.depth
of the lens in air, measured along the z-axis. The focal depth F.sub.depth
can be determined by means known to those skilled in the art. In
a conventional camera employing photographic film 13 as the image
media, the film is positioned at the focal depth F.sub.depth of
the lens. FIG. 1 illustrates film 13 positioned at the focal depth
of the lens, to provide a focused image. Known means (not shown)
such as film rails, may be employed to position film 13 at the focal
depth F.sub.depth. Hereinafter, the terminology "in-focus position"
refers to a position at which an imaging media is positioned to
provide an in-focus image.
Referring to FIG. 2, in a digital camera body 15, lens 12 is typically
mounted to the digital camera by means of camera lens mount 14.
An image sensor 16 is employed as the imaging media. Image sensor
16 comprises an imager plane 18 referring to an active surface of
the image sensor. Image sensor 16 generally further comprises an
optically transparent plate 20 (hereinafter referred to as imager
cover plate 20) having an index of refraction n. Imager plane 18
is spaced from imager cover plate 20 such that a gap or interstice
22 is interposed intermediate the imager plane and the plate. Typically,
the imager plane and the transparent plate are hermetically sealed
with a defined interstice 22.
As indicated above with regard to a conventional camera, the distance
at which lens 12 focuses light is referred to as the focal depth
F.sub.depth of the lens. However, in a digital camera, the presence
of imager cover plate 20 (disposed intermediate the lens and the
image sensor) affects the in-focus position. Accordingly, an in-focus
position F.sub.1 for imager plane 18, taking into account the presence
of imager cover plate 20, is determined by:
wherein
with t being the thickness of imager cover plate 20 and n being
the index of refraction of imager cover plate 20.
FIG. 3 provides a general illustration of a non-coherent light
interferometric measurement apparatus 21 according to the present
invention for determining the position of image sensor 16 relative
to a reference surface on the digital camera. The apparatus allows
a user to verify that the position of imager plane 18 is within
a desired tolerance. If the position of imager plane 18 is outside
the desired tolerance, the image sensor can be re-positioned to
move imager plane 18 to a desired position, such as the in-focus
position F.sub.1.
Lens 12 is generally mounted to digital camera body 15 by lens
mount 14. Conventional means (not shown) are known to facilitate
mounting of the lens to the camera body. Such means may include:
a screw lens mount wherein screw threads allows installation of
the lens to the camera body; a bayonet lens mount wherein the lens
is placed in keyed-contact and rotated over a mating flange on the
camera body with a twist of about 45 degrees; or a breechlock lens
mount wherein a knurled collar on the back of the lens fits over
a mating flange on the camera body. To secure the mounting, the
lens mount may include a locking means to lock the lens to the lens
mount. Similarly, to unlock the lens from the lens mount, an unlocking
means may be included.
In the present invention, to determine the position of imager plane
18, lens 12 is removed from digital camera body 15. Since lens 12
is removed, the position of imager plane 18 is determined relative
to a reference surface on digital camera body 15. While various
surfaces (including, but not limited to, components of the digital
camera body) may be used as a reference surface, for ease of discussion,
camera lens mount 14 will provide the reference surface. Therefore,
the position of imager plane 18 will be discussed as being determined
relative to camera lens mount 14.
Referring to FIG. 3, an optical probe assembly 24 is removably
mounted to camera lens mount 14 to securely, but temporarily, attach
optical probe assembly 24 to digital camera body 15. Preferably,
optical probe assembly 24 incorporates the means to allow the assembly
to be mounted to digital camera body 15 by means of the bayonet
lens mount wherein the assembly would slip over a mating flange
on the camera body with a twist of about 45 degrees. To temporarily
secure the mounting, a locking means 23, for example a spring loaded
locking pin, locks optical probe assembly 24 to camera lens mount
14. To unlock optical probe assembly 24 from camera lens mount 14,
an unlocking means 25 such as a spring loaded release pin, is employed
thereby allowing optical probe assembly 24 to be readily released
from digital camera body 15. Note that such locking means 23 and
unlocking means 25 may optionally be employed to lock and unlock,
respectively, lens 12 to camera lens mount 14.
Optical probe assembly 24 includes is coupled to a 1.times.2 optical
coupler 28 by a single mode optical fiber cable 26. Preferably,
connectors and patchcords (not shown) of variable length preferably
patchcords which terminate with a low back reflection connector
such an FC connector) are disposed between optical coupler 28 and
optical probe assembly 24 to permit portability for the apparatus
and to permit remote location mounting. A non-coherent light source
30, such as an LED (Light Emitting Diode), is coupled into a single
mode fiber 32 and passes through 1.times.2 optical coupler 28. A
suitable non-coherent light source 30 is a high bandwidth (approximately
40-120 nm) 1300 nm center wavelength LED having 5-100 microwatts
of coupled power.
Generally, light from non-coherent light source 30 travels along
optical fiber cable 26, transmitted through optical probe assembly
24, and is incident on image sensor 16. The light is reflected from
each of the surfaces of image sensor 16, and passes back through
optical probe assembly 24 into optical fiber cable 26. The reflected
light then passes through 1.times.2 optical coupler 28 into an optical
fiber 34, which is introduced into a non-coherent light interferometer
36. Preferably, interferometer 36 is of a Michelson configuration,
though a non-Michelson configuration has been found suitable. Associated
with non-coherent light interferometer 36 is a computing means 38,
such a computer, for controlling, collecting, manipulating, analyzing,
and storing data.
A first embodiment of optical probe assembly 24 (shown without
an optical fiber) is illustrated in FIGS. 4(a) through 4(c). Optical
probe assembly 24 comprises a probe housing 42 having a probe gripping
portion 44, at least one fiber receptacle 46 for receiving an optical
fiber (not shown), at least one angled plate 48 to position the
optical fiber (not shown), a mounting plate 50 having a plurality
of openings 52 which receive a lens (not shown), a probe insertion
portion 54 having a pellicle mounting portion 56 in which a pellicle
58 is disposed at a predetermined distance P.sub.depth from a probe
mounting surface 60. A plastic snap ring 57, for example an O-ring,
secures pellicle 58. Probe insertion portion 54 also includes a
probe mounting and locking member 51 adjacent probe mounting surface
60. An optional fiber strain relief 43 can be attached to probe
housing 42.
Generally, to assemble optical probe assembly 24, a GRIN lens (Gradient
Index lens) (not shown) is securely mounted in opening 52 in mounting
plate 50. Angled plate 48 is placed in mechanical association with
fiber receptacle 46 and then securely mounted to mounting plate
50. This subassembly in turn is securely mounted to probe insertion
portion 54.
More particularly, to assembly optical probe assembly 24, angled
plate 48 is used to ensure that the optical axis of the angled fibers
is normal to the optic axis of the probe. Fiber receptacle 46 is
preferably a modified Rifocs DAK-13/FC receptacle used to couple
to the APC/FC connectorized optical fiber. In a preferred embodiment,
a Nippon Sheet Glass (NSG) 4 mm diameter GRIN lens (P/N W40-S1111-078
N/C) is inserted into each of the five 0.159 inch diameter holes
in mounting plate 50 and locked in place with 2-56 set screws. The
GRIN lens is arranged to focus the beam of light along an axis.
As will become more apparent, the GRIN lens must have a depth of
focus sufficient to measure the physical distance between probe
mounting surface 60 and the object being positioned (e.g., the imager).
The lens-to-optical fiber distance is 7.0 mm for a 55 mm focal length.
These lenses have a length of about 4.2 mm, and an initial recess
of the lens in mounting plate 50 is set for an appropriate focal
length. A final local length adjustment is performed later if necessary.
Angled plate 48 and modified DAK-13/FC fiber receptacles 46 are
then inserted into each other so that the FC connector cutout is
oriented toward the thicker part of the angled plate and oriented
as shown in FIG. 6. The DAK-13/FC connector keys are oriented in
the same direction so that the fiber connections to the probe head
do not interfere with each other. Once oriented properly, the combined
receptacles and angled plates are mounted to the mounting plate
by means of ten 1-72 mounting screws. The assembled mounting plate
is then inserted into probe insertion portion 54 so that the two
pins and the five 1-72 threaded mounting screw holes are in proper
alignment. The assembly is locked in place with five 1-72 screws,
and probe mounting and locking member 51 is secured to probe insertion
portion 54. To align the optical probe assembly and to obtain the
correct focal length, the optical probes are tested. A single mode
optical fiber cable terminated in a Diamond FC/APC receptacle is
connected to each of the 5 modified fiber receptacles, and locked
in place using the key. The other end of the fiber cable goes to
the non-coherent light interferometer instrument for testing of
that probe. The optical probe is installed on an optical bench so
that the camera probe insertion portion is held firmly oriented
along the optical axis of the probe insertion portion.
Once the optical fibers are aligned, the plurality of fibers are
bundled together and placed in a common tube for protection. Fiber
strain relief 43 is used to protect the fibers at the point of attachment
to the optical probe assembly and to keep the fibers straight at
the connection points to the optical probe assembly.
FIGS. 5 and 6 provide further illustration of the mounting of an
angled optical fiber 62 within optical probe assembly 24. (When
angled optical fiber 26 is connectorized, it is generally denoted
as optical fiber cable 26.) As indicated above, a GRIN lens 64 has
been found suitable for use with the present invention. The focal
length of the lens is dependent on the lens to optical fiber spacing.
Angled optical fiber 62 is arranged to emit a beam of light along
its axis A. As illustrated in FIG. 5, optical fiber 62 used by Applicants
is comprised of a fiber core has a 9 .mu.m diameter and exits the
fiber at an approximate 3.8 degree angle with respect to the incoming
normal. GRIN lens 64 is disposed in the path of the beam of light
so as to direct the beam of light along an axis B normal to the
plane of the lens. As will become apparent, the beam of light along
axis B is directed toward the image sensor or object which is being
positioned within the camera. Note that the light from the optical
fiber must be centered on and parallel to the GRIN lens axis. Angled
plate 48 (best illustrated in FIG. 6) is used to ensure that the
light will be input parallel to GRIN lens axis B. A suitable optical
fiber 62 is an angle cleaved and connectorized single-mode optical
fiber. The angle cleave minimizes back reflections through the single-mode
fiber. Applicants prefer a APC/FC connector comprised of a tungsten
carbide steel which provides for reproducible fiber tip offset from
the end of the fiber when positioned within a fiber receptacle.
The tungsten steel connectors also promote reproducible focal length
with an optical probe when changing the optical fiber cable attached
to the optical probe. Rotation of the optical fiber coupling 3.8
degrees clockwise, the output light exits normal to the plane of
the GRIN lens if the incoming light emanates along the optical axis
of the lens. Note that the APC/FC connector is keyed so that angled
plate 48 is angled at an appropriate direction to direct the light
to exit normal to the axis of the GRIN lens.
Pellicle 58 is comprised of an optically transparent material which
is sufficiently thin so as to not affect the focal depth measurement.
A suitable pellicle can be made of a polyester film material of
a thickness of approximately 1-3 .mu.m, preferably 1.5 .mu.m. Means
are provided for securely mounting the pellicle to optical probe
assembly 24. For example, a plastic snap ring held in a groove provides
secure mounting to a pellicle mount. Alternatively, the pellicle
can be set in place with a suitable adhesive. For Applicants particular
application, a thin groove (not shown) is turned on an inner surface
at one end of pellicle mounting portion 56. The groove is turned
such that the pellicle will be perpendicular to the axis of the
optical probe assembly. The pellicle is preferably lightly stretched
to fit within this thin groove, and is secured using a plastic snap
ring 57. During installation of the pellicle, pellicle mounting
portion 56 is placed in a fixture such that the grooved end is in
a horizontal plane and facing upward. The pellicle is stretched
across the end of the pellicle mounting portion, and plastic snap
ring 57 is inserted into the groove and snapped in place. Heat,
as such from a heat gun, may be used to even the tension in the
pellicle.
As illustrated in FIG. 4(c), for the present invention, pellicle
58 can be replaced with an optically transparent material, for example
a glass plate 59 of approximately 4-7 mm in thickness, so long as
the optical path through the glass plate (nt) is larger than the
maximum scan distance scanned with the interferometer. The pellicle
(or glass plate) is disposed intermediate the reference surface
on the camera (described above as being the lens mount) and the
image sensor or object being positioned within the camera. Note
that while the pellicle is sufficiently thin to have only one reference
surface, when glass plate 59 is used, it's second surface (i.e.,
the surface adjacent the imager) is used as the reference surface.
Also note that when glass plate 59 is used, the effective focal
length in air of the lens is increased. Therefore, a shorter focal
length is used when glass plate 59 is utilized. For example, an
approximate 2 mm focus shift may occur with a 6 mm thick glass plate
having an index of refraction of approximately 1.5.
As with the pellicle, means are provided for securely mounting
glass plate 59 to optical probe assembly 24. For Applicants particular
application, a groove (not shown) as thick or slightly thicker than
the glass plate is turned on an inner surface at one end of pellicle
mounting portion 56. The groove is turned such that the glass plate
will be perpendicular to the axis of the optical probe assembly.
The diameter of the glass plate is arranged so as to fit tautly
in the grooved surface. Once inserted into the groove, the glass
plate is secured, for example, using an optimal optic cement (preferably
uv curing).
Preferably, a plurality of optic fibers are employed. As illustrated
in FIG. 4(a), angled plate 48 and fiber receptacle 46 are configured
for five optic fibers. Five optical fibers are preferred so as to
be able to determine the flatness of an image sensor mounted in
a digital camera and to be able to determine whether an image sensor
mounted in a digital camera is parallel relative to a reference
surface on the digital camera. The five optical fibers define the
five measurement locations. Typically, a center location, and four
locations near the corners of the imager are used.
In some instances, where it is desired to measure points at different
locations which are spaced closely together on an imager surface,
the connectorized fibers arrangement may not be suitable. Therefore,
in a second embodiment of optical probe assembly 24, illustrated
in FIGS. 7(a)-7(f), fiber receptacle 46 and angled plate 48 are
replaced by a probe chuck 61. Accordingly, the connectorized APC/FC
fibers are replaced by bare APC/FC ferrules 63. Such a probe chuck
arrangement provides for an exact constraint mounting to ensure
that the optical axis of the optical fiber is normal to the optic
axis of the optical probe assembly. Referring to FIGS. 7(a) and
7(b), in a preferred arrangement, a 0.25 inch diameter fiber chuck
has, at one end, a 2 mm diameter through hole at a length of 20
mm. A 2.5 mm hole 65, angled at approximately 3.78 degrees from
normal is tapped at the same end so as to receive the optical fiber
ferrule 63. At the other end of fiber chuck 61 is disposed a 4 mm
diameter hole by which to receive a 4 mm 4.12 mm long GRIN lens
64, best illustrated in FIG. 7(d). APC/FC ferrule 63 is used to
mount the optical fiber in probe chuck 61. As with the first embodiment,
in the second embodiment, angled optical fiber 62 is oriented in
probe chuck 61 to emit a beam of light along an axis normal to the
reference surface toward the object.
In the second embodiment, the mounting plate which holds probe
chuck 61 is illustrated in FIGS. 7(c), 7(e), and 7(f) as mounting
plate 50'. As illustrated in FIGS. 7(a)-7(e), probe chuck 61 is
larger in diameter at one of its ends to facilitate mounting of
probe chuck 61 in mounting plate 5'. As such, the second embodiment
differs from the first embodiment in that the probe chuck 61 supports
the optical fiber and GRIN lens 64. The dimension of probe chuck
61 having the larger diameter is cut to a length so as to place
the GRIN lens at an appropriate focal length for the measurement.
This second embodiment can be used with both the pellicle and glass
plate. To assemble the second embodiment, ferrule 63 is inserted
into hole 65 and secured with an allen 2-56 screw. The ferrule is
inserted into angled hole 65 such that its orientation duplicates
that of FIG. 6. Once fully inserted, light emits parallel to the
axis of probe chuck 61. A GRIN lens is inserted fully into a hole
67 (as shown in FIG. 6) and secured with an allen 2-56 screw. The
length of probe chuck 61 is such that the fiber-to-lens spacing
is set automatically for the appropriate focal length when ferrule
63 and the GRIN lens are each fully retained into their respective
holes. Probe chuck 61 is then fully inserted into openings 52' of
mounting plate 50'. When fully inserted, the entire structure is
at the appropriate focal length. Once attachment is made to probe
insertion portion 54, the remaining assembly is similar to that
of the first embodiment.
Note that precision machining of probe chuck 61 promotes ready
and easy alignment and assembly of the second embodiment.
For both the first and second embodiments, when optical probe assembly
24 is removably mounted to digital camera body 15, probe mounting
surface 60 is at a predetermined orientation relative to a reference
surface on digital camera body 15. As discussed above, for discussion
purposes, the reference surface will be lens mount 14. Accordingly,
in Applicants' arrangement, probe mounting surface 60 abuts camera
lens mount 14 when probe mounting and locking member 51 is locked
in place. Therefore, probe mounting surface 60 is at a predetermined
distance from the reference surface on the digital camera body of
0.0 units.
With optical probe assembly 24 mounted to digital camera body 15,
the orientation of optical fiber 62, GRIN lens 64, and image sensor
16 are as illustrated in FIG. 8. Pellicle 58 (or glass plate 59)
is disposed at a predetermined depth P.sub.depth from probe mounting
surface 60 and, accordingly, lens mount 14 (generally illustrated
in FIG. 8 as the reference surface positioned at Reference Plane
C). The physical distance from a front surface 66 to a back surface
68 of imager cover plate 20 is the thickness of the imager cover
plate. The depth from pellicle 58 to front surface 66 of imager
cover plate 20 is referred to as PG.sub.depth, while the depth from
back surface 68 of imager cover plate 20 to imager plane 18 is referred
to as GS.sub.depth. Accordingly, the actual depth D.sub.actual of
imager plane 18 relative to the reference surface (i.e., lens mount
14 at Reference Plane C) is:
where t is the thickness of imager cover plate 20;
The corresponding total optical depth D.sub.optical from pellicle
58 (or glass plate 59) relative to the reference surface (i.e.,
lens mount 14 at Reference Plane C) is given by the equation:
where n is the index of refraction of imager cover plate 20.
Substituting Equation 3 into Equation 4 results in:
Accordingly, the difference between where imager plane 18 is actually
positioned (i.e., D.sub.actual) and the desired position, for example
the in-focus position F.sub.1 (from Equation 1), is referred to
as the difference in focus D.sub.F :
With the optical probe assembly locked to the digital camera in
a predetermined orientation whereby the pellicle (or the glass plate)
is disposed at a known reference depth relative to the reference
surface on the digital camera, non-coherent light interferometry
can be utilized as disclosed in U.S. Pat. No. 5,757,485 (Marcus
et al) and U.S. Pat. No. 5,757,486 (Marcus et al), commonly assigned
and incorporated herein by reference, to determine (i) the depth
from the reference surface to the front surface of the imager cover
plate, (ii) the optical thickness of the imager cover plate, and
(iii) the depth from the back surface of the imager cover plate
to the image sensor. From this information, the position of imager
plane 18 relative to the reference surface can be determined.
Note that for the present invention, a 55-mm focal length was selected
for the design focal distance. Table I shows the required fiber
to lens spacing, resulting focal diameter, focal depth and acceptance
cone angle for a range of focal lengths around the value selected
for the measurement geometry. Other focal lengths can be used, as
shown in Table I, so long as the focal length is greater than the
imager-to-lens mount spacing in the camera. The distance from the
GRIN lens in the mounting fixture to the imager plane in the cameras
determines the required focal length.
Also shown in Table I is the focal depth and acceptance angle for
the lens as a function of focal length. It is observed that the
acceptance angle is improved over a collimated design, which has
an acceptance angle of less than 0.1 degree. This improved acceptance
angle provides for the measurement of imagers with a large degree
of tilt which will not focus properly when mounted into a camera
body.
TABLE I NSG 4.0 mm W40-S1111-078 N/C Lens Parameters Lens to Focal
Acceptance Focal length Fiber diameter focal depth angle fwhm (mm)
Spacing (.mu.m) (mm) (degrees) 50 6.952 55.702 3.749 0.709 51 6.927
56.963 3.921 0.693 52 6.902 58.223 4.096 0.678 53 6.879 59.483 4.275
0.664 54 6.856 60.743 4.458 0.650 55 6.835 62.003 4.645 0.637 56
6.814 63.264 4.836 0.624 57 6.794 64.524 5.031 0.612 58 6.775 65.784
5.229 0.600 59 6.757 67.044 5.431 0.589 60 6.739 68.304 5.637 0.578
The invention has been described in detail with particular reference
to a presently preferred embodiment, but it will be understood that
variations and modifications can be effected within the spirit and
scope of the invention. The presently disclosed embodiments are
therefore considered in all respects to be illustrative and not
restrictive. The scope of the invention is indicated by the appended
claims, and all changes that come within the meaning and range of
equivalents thereof are intended to be embraced therein. cl PARTS
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