Digital Camera Patent Abstract
In a digital camera having an image sensor and a lens defining an
optical axis for focusing an image upon a focal plane, an image
sensor mount includes the digital camera having a housing for mounting
the lens and defining a first opening through which an image can
be focused by the lens and transmitted along the optical axis, and
an image sensor assembly including the image sensor attached to
an image sensor mounting plate. The image sensor mount further includes
a camera mounting plate having first and second surfaces, the first
surface being fixedly attached to the camera housing and defining
a second opening through the first and second surfaces which is
aligned with the first opening, the camera mounting plate including
at least three spaced-apart alignment elements on the second surface,
the alignment elements being located at a predetermined position
relative to the lens; and an image sensor mounting plate for attaching
the image sensor assembly to the camera mounting plate so that the
image sensor mounting plate engages the alignment elements to center
the image sensor with respect to the optical axis at the focal plane.
Digital Camera Patent Claims
What is claimed is:
1. In a digital camera having an image sensor and a lens defining
an optical axis for focusing an image upon a focal plane, an image
sensor mount comprising: (a) the digital camera having a housing
for mounting the lens and defining a first opening through which
an image can be focused by the lens and transmitted along the optical
axis; (b) an image sensor assembly including the image sensor attached
to an image sensor mounting plate; (c) a camera mounting plate having
first and second surfaces, the first surface being fixedly attached
to the camera housing and defining a second opening through the
first and second surfaces which is aligned with the first opening
when the camera mounting plate is mounted to the camera housing,
the camera mounting plate including at least three spaced-apart
alignment elements on the second surface, the alignment elements
being protrusions located at a predetermined position relative to
the lens; and (d) the image sensor mounting plate being attached
to the camera mounting plate so that the image sensor mounting plate
engages the alignment elements to center the image sensor with respect
to the optical axis at the focal plane.
2. The image sensor mount according to claim 1 wherein the camera
mounting plate is fixedly attached to the camera housing by an adhesive.
3. In a digital camera having an image sensor and a lens defining
an optical axis for focusing an image upon a focal plane, an image
sensor mount comprising: (a) the digital camera having a housing
for mounting the lens and defining a first opening through which
an image can be focused by the lens and transmitted along the optical
axis, the housing including first and second camera pins; (b) an
image sensor assembly including the image sensor attached to an
image sensor mounting plate; (c) a camera mounting plate having
first and second surfaces, the first surface being fixedly attached
to the camera housing and defining a second opening through the
first and second surfaces which is aligned with the first opening
when the camera mounting plate is mounted to the camera housing,
the camera mounting plate including at least three spaced-apart
alignment elements on the second surface, the alignment elements
being located at a predetermined position relative to the lens,
and further including a slot for alignment with the first camera
pin and a defining hole for alignment with the second camera pin;
and (d) the image sensor mounting plate being attached to the camera
mounting plate so that the image sensor mounting plate engages the
alignment elements to center the image sensor with respect to the
optical axis at the focal plane.
4. The image sensor mount according to claim 3, wherein the camera
mounting plate defines at least three fastening holes, and the image
sensor mounting plate defines at least three corresponding fastening
holes, and further including at least three screws passing through
the corresponding holes in the image sensor mounting plate and the
camera mounting plate, respectively, for securing the image sensor
to the camera housing.
5. The image sensor mount according to claim 4, wherein the at
least three fastening holes on the camera mounting plate are each
positioned within a maximum range of approximately 3.25 mm of an
alignment element, to substantially minimize deflection of the camera
mounting plate when the image sensor mounting plate is attached
to the camera mounting plate.
6. The image sensor mount according to claim 3, wherein the alignment
elements are protrusions.
7. The image sensor mount according to claim 3, wherein the camera
mounting plate is fixedly attached to the camera housing by an adhesive.
Digital Camera Patent Description
FIELD OF THE INVENTION
This invention relates generally to the field of digital cameras,
and in particular, to a mount for aligning an image sensor to an
optical axis of the digital camera.
BACKGROUND OF THE INVENTION
High resolution digital cameras have been developed for professional
photographers, whose business depends on taking high quality pictures.
These cameras often use existing 35 mm or medium-format film camera
bodies and lenses, together with a customized electronic imaging
back that replaces the removable film back ordinarily supplied with
the camera. An example is the Kodak DCS 460.TM. digital camera,
which is based upon the Nikon N90s single lens reflex (SLR) camera
body. This system, which is compatible with all Nikon lenses and
accessories, allows photographers to easily operate the digital
camera, and to use their existing equipment with the camera. However,
the photosensitive area of the image sensor is often smaller than
the film area, and therefore, smaller than the image plane. As a
result, the relative magnification of the lens is larger than for
35 mm film.
A problem with this type of camera is the alignment of the image
sensor to the optical axis of the camera body. For a non-SLR camera,
where the image sensor may be an integral part of an optical assembly,
the alignment technique in Japanese Patent Application 61-245773
can be used. Two positioning pins are provided to the rear end of
a lens barrel, and are pressed into contact with a ceramic package
containing the image sensor in order to optically position the image
sensor at an image plane of a lens assembly. However, in an SLR
camera system, the image sensor cannot physically locate to the
lens assembly because the lens, which is removable, is separated
from the image plane by a movable mirror used for through-the-lens
viewing.
Consequently, in a camera back system using a film body, the image
sensor needs to be referenced to the film plane. For example, as
shown in U.S. Pat. No. 5,483,284, an image sensor package possesses
four positioning pins at four corners thereof that touch a guide
rail plane of an aperture in the camera body. With this arrangement,
the image sensor package is precisely located at the focal plane
of the lens assembly, i.e., in the z-direction. However, it is difficult
to prevent x-y misalignment, which in turn prevents accurate centering
of the image sensor package relative to the optical axis of the
lens assembly.
An imager mounting plate can also be used to support the image
sensor against the camera guide rails at the focal plane of the
lens assembly. The imager mounting plate can then be secured to
the camera guide rails using a pin and hole configuration to provide
x-y alignment. However, the camera guide rails are typically made
of either machine steel or molded plastic. Providing alignment holes
in machine steel rails would result in increased manufacturing costs.
Plastic molded rails, although less expensive to manufacture, do
not provide sufficient accuracy of alignment of the image sensor
at the focal plane of the lens assembly, and do not allow for interchangeability
of the image sensor for servicing. Further, in a camera back system
using a film body, warping or deflections in the camera guide rails
or in the imager mounting plate can often cause distortions in the
digital images.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide
an image sensor mount for a digital camera for accurate alignment
of the image sensor at the focal plane of the lens assembly.
It is another object of the present invention to provide an image
sensor mount for a digital camera which enables ease of replacement
and serviceability of the image sensor without using camera guide
rails.
It is yet another object of the present invention to provide an
image sensor mount for a digital camera which substantially removes
any distortions in the digital images.
It is a further object of the present invention to provide an image
sensor mount for a digital camera which eliminates the need for
mounting holes in the camera housing.
These objects are achieved in a digital camera having an image
sensor and a lens defining an optical axis for focusing an image
upon a focal plane, an image sensor mount comprising: (a) the digital
camera having a housing for mounting the lens and defining a first
opening through which an image can be focused by the lens and transmitted
along the optical axis; (b) an image sensor assembly including the
image sensor attached to an image sensor mounting plate; (c) a camera
mounting plate having first and second surfaces, the first surface
being fixedly attached to the camera housing and defining a second
opening through the first and second surfaces which is aligned with
the first opening when the camera mounting plate is mounted to the
camera housing, the camera mounting plate including at least three
spaced-apart alignment elements on the second surface, the alignment
elements being located at a predetermined position relative to the
lens; and (d) the image sensor mounting plate being attached to
the camera mounting plate so that the image sensor mounting plate
engages the alignment elements to center the image sensor with respect
to the optical axis at the focal plane.
ADVANTAGES
It is an advantage of the present invention to provide an image
sensor mount for a digital camera which enables interchangeability
of the image sensor for servicing, while maintaining proper focus
alignment accuracy.
It is another advantage of the present invention to provide an
image sensor mount for a digital camera which does not introduce
any distortions in the digital images.
It is yet another advantage of the present invention to provide
an image sensor mount for a digital camera which does not require
the use of camera guide rails or of mounting holes in the camera
housing, thereby reducing manufacturing cost and complexity.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic of a digital camera in accordance with the
present invention, showing a back enclosure attached to a camera
housing;
FIG. 2 is a rear view of the digital camera shown in FIG. 1 with
the back enclosure removed and showing details of the alignment
of a camera mounting plate to the digital camera in accordance with
the present invention;
FIG. 3 shows an image sensor mounting plate, an image sensor, and
a circuit board in accordance with the present invention for use
with the digital camera shown in FIGS. 1 and 2; and
FIG. 4 shows an imager assembly including the components shown
in FIG. 3 and showing details of the alignment of the image sensor
mounting plate to the camera mounting plate of FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
Because imaging devices employing electronic sensors are well known,
as are single lens reflex cameras and related components, the present
description will be directed in particular to elements forming part
of, or cooperating more directly with, apparatus in accordance with
the present invention. Elements not specifically shown or described
herein may be selected from those known in the art.
Beginning with FIG. 1, a digital camera 10 is shown mainly in schematic
form to include a housing 12 and a back enclosure 14. Although the
digital camera 10 is a fully integrated unit in the sense that the
back enclosure 14 is not intended to be removable by the photographer,
the housing 12 is a conventional 35 mm single lens reflex (SLR)
film camera body, such as a Nikon N90s SLR camera body. FIG. 2 shows
a rear view of the housing 12 as would be seen during the assembly
operation. Referring to FIGS. 1 and 2 together as appropriate, the
housing 12 includes a lens 16, typically interchangeable, for directing
image light along an optical axis 18 towards a pivotable mirror
20, and a lens mount 17. When the pivotable mirror 20 is in its
down position, as shown in FIG. 1, the image light is directed upward
toward an optical viewfinder 22. A viewfinder image, which is formed
on a focusing screen 24, is viewed through an eyepiece 26 and a
prism 28. When the pivotable mirror 20 is raised to the position
20', the image light is directed through an opening 30 (shown in
FIG. 2) which cooperates with a focal plane shutter 31, and forms
an image on a focal plane 32.
In accordance with the present invention and as shown in FIG. 2,
a first camera pin 34 is located above the focal plane shutter 31,
and a second camera pin 36 is located below the focal plane shutter
31. A camera mounting plate 38 is positioned parallel to the lens
mount 17, and is fixedly attached to the housing 12 at the focal
plane 32 by, preferably, an adhesive. Other attaching arrangements
can be used as well. Preferably, the camera mounting plate 38 is
made of stainless steel.
The camera mounting plate 38 will now be described in more detail
with reference to FIG. 2. It will be appreciated by those skilled
in the art that the camera mounting plate 38 replaces the conventional
film rails used in a film camera to support a film at the focal
plane. As shown in FIG. 2, the camera mounting plate 38 defines
an opening 40 which is aligned with the focal plane shutter 31 of
the camera housing 12 at the focal plane 32. An alignment slot 42
and an alignment hole 44 formed on the camera mounting plate 38
correspond to the first and second camera pins 34 and 36, respectively,
for fixedly attaching a first surface 47 of the camera mounting
plate 38 to the camera housing 12. The alignment slot 40 and alignment
hole 42 provide for alignment of an image sensor 46 (shown in FIG.
3) to the camera mounting plate 38 in the x, y, and theta z directions.
The x, y, z, and theta z directions are shown in FIG. 1. Theta z
shows a range of angles relative to the z-axis. Similarly, there
are theta x and theta y directions which are not shown for clarity
of illustration.
The camera mounting plate 38 is then adhesively bonded to the camera
housing 12 to provide alignment of the image sensor 46 in the z,
theta x, and theta y directions. At least three spaced-apart alignment
elements 50, 52, and 54 on a second surface 48 of the camera mounting
plate 38 are located a predetermined position relative to the lens
mount 17, and thus, to the lens 16. Preferably, the alignment elements
50, 52, and 54 are protrusions which extend outwardly a minimum
of approximately 0.38 mm from the second surface 48 of the camera
mounting plate 38. The alignment elements 50, 52, and 54 are preferably
located .+-.0.038 mm relative to each other to provide alignment
of the image sensor 46 in the z, theta x, and theta y directions
to control the depth of focus of the camera 10. Alternatively, the
alignment elements 50, 52, and 54 could be positioned on the image
sensor mounting plate 60 rather than on the camera mounting plate
38. Preferably, the alignment elements 50, 52, and 54 are semi-circular
in shape. However, the alignment elements 50, 52, and 54 could take
on various shapes to facilitate alignment of the image sensor 46.
Referring now to FIG. 3, an image sensor mounting plate 60 supports
the image sensor 46 in a central region thereof. In accordance with
the present invention, the image sensor 46 is optically aligned
and adhesively bonded to the image sensor mounting plate 60 in a
well-known manner. The image sensor 46 and image sensor mounting
plate 60 are then soldered to a circuit board 62 containing conventional
circuitry for operating the image sensor 46 and for providing camera
functions. This resulting imager assembly 64 (i.e., the image sensor
mounting plate 60, the image sensor 46, and the circuit board 62),
which is shown in FIG. 4, is then mounted to the camera mounting
plate 38 so that the image sensor mounting plate 60 engages the
protrusions 50, 52, and 54 on the camera mounting plate 38. An alignment
slot 61 and an alignment hole 63 formed in the image sensor mounting
plate 60 correspond to the alignment slot 42 and the alignment hole
44, respectively, on the camera mounting plate 38, and to the first
and second camera pins 34 and 36, respectively, on the camera housing
12. This arrangement attaches the imager assembly 64 to the camera
mounting plate 38. The alignment slot 61 and alignment hole 63 provide
for alignment of the imager assembly 64, and thus, the image sensor
46 to the camera mounting plate 38 in the x, y, and theta z directions.
Further, by mounting the imager assembly 64 to the camera mounting
plate 38 with reference to the protrusions 50, 52, and 54, the imager
assembly 64, and thus, the image sensor mounting plate 60 are aligned
in the z, theta x, and theta y directions. In this manner, the image
sensor 46 is accurately centered with respect to the optical axis
18 of the lens 16 at the focal plane 32.
The image sensor mounting plate 60 is secured to the camera mounting
plate 38 by at least three fasteners (shown in FIG. 4), which preferably
are screws 56. These screws 56 pass through at least three corresponding
tapped fastening holes 66 (shown in FIG. 3) on the image sensor
mounting plate 60. The screws 56 are secured in at least three corresponding
threaded fastening holes 68 (shown in FIG. 2) on the camera mounting
plate 38. In accordance with the present invention and as can be
seen in FIG. 2, the at least three threaded fastening holes 68 on
the camera mounting plate 38 are each positioned substantially close
to one of the three protrusions 50, 52, and 54. This structure minimizes
any moment on the camera mounting plate 38 and thereby substantially
eliminates any deflection of the camera mounting plate 38 when the
imager assembly 64 is attached to the camera mounting plate 38.
Preferably, three screws 56 are used, and the threaded fastening
holes 68 on the camera mounting plate 38 are each positioned within
a maximum range of approximately 3.25 mm of a protrusion.
It will be appreciated by those skilled in the art that the present
invention including the three protrusions 50, 52, and 54 on the
camera mounting plate 38 provide for ease of serviceability and
replacement of the imager assembly 64 while maintaining substantially
no change in the z, theta x, and theta y directions. Thus, the focus
and sharpness of the images captured by the digital camera 10 can
be maintained. Further, since the protrusions 50, 52, and 54 are
located a predetermined position relative to the lens 16, the image
sensor 46 is accurately centered with respect to the optical axis
18 of the lens 16 at the focal plane 32. Accordingly, alignment
of the image sensor 46 is independent of the actual image sensor
that is used. In addition, the present invention substantially eliminates
any distortions in the images captured by the digital camera 10
that may be caused by warping or deflections in the camera mounting
plate 38 or the image sensor mounting plate 60.
The invention has been described in detail with particular reference
to a certain preferred embodiment thereof, but it will be understood
that variations and modifications can be effected within the spirit
and scope of the invention.
PARTS LIST 10 digital camera 12 housing 14 back enclosure 16 lens
17 lens mount 18 optical axis 20 pivotable mirror 22 optical viewfinder
24 focusing screen 26 eyepiece 28 prism 30 opening 31 focal plane
shutter 32 focal plane 34 first camera pin 36 second camera pin
38 camera mounting plate 40 opening 42 alignment slot 44 alignment
hole 46 image sensor 47 first surface 48 second surface 50 alignment
element 52 alignment element 54 alignment element 56 fastener 60
image sensor mounting plate 61 alignment slot 62 circuit board 63
alignment slot 64 imager assembly 66 tapped fastening hole 68 threaded
fastening hole
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