Digital Camera Patent Abstract
A terrestrial telescope with digital camera includes objective lenses,
an imaging element located downstream of the objective lenses, a
retractable optical-path splitter between the objective lenses and
the imaging element, and an optical system for observing an optical
image divided from the optical path of the imaging optical system
by the optical-path splitter. An optical element is inserted into
the optical axis of the imaging optical system to correct for any
change in the image-formation position when the optical-path splitter
is retracted from the optical path of the imaging optical system
during imaging. Digital Camera Patent Claims
What is claimed is:
1. A terrestrial telescope with a digital camera comprising: a
group of objective lenses; an imaging optical system having an optical
path and including the group of objective lenses and an imaging
element disposed along the optical path at a position at which an
image of a subject is formed by the group of objective lenses; an
optical-path-splitting means disposed on the optical path of the
imaging optical system between the group of objective lenses and
the imaging element so as to be retractable from the optical path
of the imaging optical system during imaging; an observation optical
system for observing an optical image of the subject via the optical-path-splitting
means disposed on the optical path of the imaging optical system;
and imaging position correction means including an optical element
insertable into the optical path of the imaging optical system to
correct for any change in image-formation position when the optical-path-splitting
means is retracted from the optical path of the imaging optical
system during imaging.
2. A terrestrial telescope with a digital camera according to claim
1; wherein the optical element comprises a plane glass element having
a thickness effective to correct for a change in image-formation
position produced by retraction of the optical-path-splitting means.
3. The A terrestrial telescope with a digital camera according
to claim 2; wherein the plane glass element is inserted perpendicularly
to the optical path of the imaging optical system.
4. A terrestrial telescope with a digital camera according to claim
2; wherein the thickness of the plane glass element is determined
based on disposing the optical-path-splitting means at a certain
angle on the optical path of the imaging optical system.
5. A terrestrial telescope with a digital camera according to claim
4; wherein the certain angle is 45.degree..
6. A terrestrial telescope with a digital camera according to claim
1; wherein retraction of the optical-path-splitting means and insertion
of the optical element are controlled by a guide lever that supports
the imaging position correction means on one end and the optical-path-splitting
means on another end.
7. A terrestrial telescope with a digital camera according to claim
1; wherein the optical element has one or more prescribed optical
filter characteristics.
8. A terrestrial telescope with a digital camera according to claim
7; wherein the one or more prescribed optical filter characteristics
comprise one or more of infrared light-blocking filter characteristics,
spatial frequency filter chacacteristics polarizing filter characteristics
and ND filter characteristics.
9. A terrestrial telescope with a digital camera according to claim
1; wherein the optical-path-splitting means has one or more prescribed
optical filter characteristics imparted to the side of the optical-path-splitting
means from which light exits to the imaging element.
10. A terrestrial telescope with a digital camera according to
claim 9; wherein the one or more prescribed optical filter characteristics
comprise one or more of infrared light-blocking filter characteristics,
spatial frequency filter characteristics, polarizing filter characteristics
and ND filter characteristics.
11. A terrestrial telescope with a digital camera comprising: a
group of objective lenses for forming an optical image of a subject
and transmitting the optical image along an optical axis; an imaging
optical system disposed along the optical axis and including the
group of objective lenses and an imaging element; an observation
optical system for observing the optical image of the subject transmitted
by the group of objective lenses; an optical splitter mounted to
undergo movement between (1) a first position in which the optical
splitter is inserted into the optical axis between the group of
objective lenses and the imaging element and directs a split portion
of the optical image transmitted by the group of objective lenses
to the imaging element so that the optical image is focused on the
image element at a position deviated from a position at which the
optical image would be focused if the optical splitter were not
inserted into the optical axis and directs another split portion
of the optical image to the observation optical system to enable
observation of the optical image, and (2) a second position in which
the optical splitter is retracted from the optical axis; and an
optical correction element movable into the optical axis when the
optical splitter is in the second position to correct for deviation
of the focus position of the optical image of the subject caused
by retraction of the optical splitter from the optical axis and
movable out of the optical axis when the optical splitter is in
the first position.
12. A terrestrial telescope with a digital camera according to
claim 11; wherein the optical splitter directs a substantially greater
split portion of the optical image to the observation optical system
than to the imaging element.
13. A terrestrial telescope with a digital camera according to
claim 11; further including a movable lever, the optical splitter
and the optical correction element being mounted to the lever at
different locations so that movement of the lever in one direction
moves the optical splitter to the first position while moving the
optical correction element out of the optical axis and movement
of the lever in a direction opposite to the one direction moves
to the optical splitter to the second position while moving the
optical correction element into the optical axis.
14. A terrestrial telescope with a digital camera according to
claim 13; wherein lever has two generally opposite ends and is mounted
to undergo movement about an axis located between the two ends,
the optical splitter being mounted to one of the ends and the optical
correction element being mounted to the other of the ends.
15. A terrestrial telescope with a digital camera according to
claim 13; wherein the optical splitter and the optical correction
element are disposed on the lever such that the optical splitter
intersects the optical axis at an angle of 45.degree. when in the
first position and the optical correction elements intersects the
optical axis at an angle of 90.degree. when moved into the optical
axis.
16. A terrestrial telescope with a digital camera according to
claim 11; wherein the optical correction element comprises a glass
element having a predetermined thickness effective to correct for
deviation of the focus position of the optical image caused by retraction
of the optical splitter from the optical axis.
17. A terrestrial telescope with a digital camera according to
claim 16; wherein the predetermined thickness of the glass element
is determined based on an angle at which the optical splitter intersects
the optical axis when in the first position.
18. A terrestrial telescope with a digital camera according to
claim 17; wherein the angle at which the optical splitter intersects
the optical axis when in the first position is 45.degree..
19. A terrestrial telescope with a digital camera according to
claim 17; wherein the glass element comprises a plane glass element
which intersects the optical axis perpendicularly when moved into
the optical axis.
20. A terrestrial telescope with a digital camera according to
claim 11; wherein the optical splitter comprises a quick-return
half-mirror which, when inserted into the optical axis, transmits
a split portion of the optical image to the imaging element and
reflects another split portion of the optical image to the observation
optical system.
Digital Camera Patent Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a terrestrial telescope with a
digital camera that uses a means of splitting the optical path so
that the optical path goes to the imaging element and the observation
optical system.
2. Description of the Prior Art
Terrestrial telescopes having a magnification factor ranging from
about 20 to 60 are used extensively for observing wild birds and
other fauna. Terrestrial telescopes include those based on a Galilean
telescope configuration comprising a positive (convex) lens and
a negative (concave) lens that functions as an erecting system,
and those based on a Keplerian telescope configuration comprising
just a positive (convex) lens, to which are added prisms or other
such elements to constitute an erecting system. Both types of telescope
enable a user to observe an erect image.
As well as being able to use such telescopes to observe natural
flora and fauna, users want to be able to record the images they
are seeing. In Japanese Patent Application No. 2002-47304, the present
applicant proposed a configuration for a terrestrial telescope with
a digital camera that is able to record an observed image.
In the above mentioned Japanese Application the structure of the
main optical system except for the observation optical system is
similar to that of a single lens reflex camera, and the optical
system uses a total-reflection quick-return mirror. Unlike a single
lens reflex camera that uses silver-halide film, a single lens reflex
digital camera uses a fixed half-mirror to split the optical path
so that the beam transmitted by the imaging lens goes to the observation
optical system and the imaging element. This makes it possible to
continuously use images on the imaging element for display on a
monitor, auto-focus processing, calculating exposure, and so forth,
and because there is no movable mirror, the configuration can be
made simple and low-cost. On the other hand, this configuration
reduces the amount of light.
In this respect, Japanese Patent Laid-Open Publication No. 2000-162495
discloses an optical system in which a half-mirror constituted as
a quick-return mirror is used to deflect part of the light beam
from the subject through the objective lens to the observation optical
system and the rest of the beam to the imaging element. In this
Publication, the half-mirror is normally located at an observation
position at which it deflects part of the subject light beam to
the observation optical system and is controlled during imaging
to be removed from the imaging optical path. When the half-mirror
is in the observation position, the imaging element receives a beam
through the half-mirror and photo-electrically converts it to calculate
and memorize the focusing position of the objective lens when the
half-mirror will be retracted. When the half-mirror is actually
retracted to the imaging position during the imaging, the objective
lens is moved to the calculated focus position.
The configuration disclosed by Japanese Patent Laid-Open Publication
No. 2000-162495 is advantageous in that it avoids light loss during
the imaging of the subject and can move the imaging lens to correct
a focusing error arising when the half-mirror is retracted. However,
it also has drawbacks in that a processor and memory are required
for calculating and storing the focus position, which increases
the manufacturing cost.
An object of the present invention is therefore to provide a terrestrial
telescope with a digital camera that enables the imaging element
to continuously perform imaging without loss of light, and in which
the focus position of the imaging element can be corrected with
a simple and low-cost configuration.
SUMMARY OF THE INVENTION
A terrestrial telescope with a digital camera according to the
invention comprises a group of objective lenses; an imaging optical
system including the group of objective lenses and an imaging element
disposed at a position at which an image of a subject is formed
by the group of objective lenses; an optical-path-splitting means
disposed on the optical path of the imaging optical system between
the group of objective lenses and the imaging element so as to be
retractable from the optical path of the imaging optical system
during imaging; an observation optical system for observing an optical
image of the subject via the optical-path-splitting means disposed
on the optical path of the imaging optical system; and an imaging
position correction means including an optical element that is inserted
into the optical axis of the imaging optical system to correct for
any change in image-formation position when the optical-path-splitting
means is retracted from the optical path of the imaging optical
system during imaging.
The optical element can be comprised of a plane glass element of
a thickness that corrects for the change in image-formation position
arising when the optical-path-splitting means is retracted.
The retraction of the optical-path-splitting means and the insertion
of the optical element can be controlled by means of a guide lever
that supports the imaging position correction means on one end and
the optical-path-splitting means on the other end.
Prescribed optical filtering characteristics can be imparted to
the optical element and to the side of the optical-path-splitting
means from which light exits to the imaging element.
The plane glass element can be inserted perpendicularly to the
optical axis of the imaging optical system.
Further features of the invention, its nature and various advantages
will be more apparent from the accompanying drawings and following
detailed description of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an explanatory view showing the general configuration
of a terrestrial telescope with a digital camera according to the
present invention;
FIG. 2 is an explanatory view showing the quick-return half-mirror
inserted into the main optical system during observation in the
apparatus of FIG. 1;
FIG. 3 is an explanatory view showing the plane glass element inserted
into the main optical system during imaging in the apparatus of
FIG. 1; and
FIG. 4 is a table showing the amounts of image deviation produced
by the quick-return half-mirror in the apparatus of FIG. 1, and
the corresponding calculated thicknesses of the plane glass element
used to correct the deviation.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows the main parts of the terrestrial telescope with a
digital camera configured according to the present invention. In
FIG. 1, a group of objective lenses 1 comprises a fixed lens group
1a and a movable focusing lens group 1b. A light beam transmitted
by the group of objective lenses 1 falls incident on an optical
beam splitter in the form of a quick-return half-mirror (shortened
to "QR half-mirror" hereinbelow) 2 that normally intersects
the main optical axis (the optical axis of the group of objective
lenses 1) at an angle of 45 degrees. The movable focusing lenses
group 1b is maintained by a lenses frame 17 and can be moved along
the main optical axis by an AF (automatic focusing) motor 16.
The portion of the beam of light transmitted by the QR half-mirror
2 impinges on an imaging element (such as a CCD or CMOS imaging
element) 3 located on the focal plane. The portion of the beam of
light reflected by the QR half-mirror 2 impinges on the observation
optical system and, via an erecting optical system composed of a
combination of a penta roof prism (not shown) or a reflecting mirror
4 and a relay lens 5, forms an image on a reticle 6 located at a
position that is a conjugate to that of the focal plane. A user
can observe the erect image via an ocular 7.
The reflectance of the QR half-mirror 2 is arbitrary. However,
a reflectance of 80% to 90% is used so that most of the light goes
to the observation optical system, facilitating observation by a
user. The QR half-mirror 2 is affixed to a mirror holder 8a provided
on an end of a mirror guide lever 8 of metal or glass. The mirror
guide lever 8 can rotate about an axis of rotation 12. A plane glass
holder 8b is provided on the opposite end of the mirror guide lever
8 located at the other side of the axis of rotation 12. A plane
glass 9 is affixed to the plane glass holder 8b. The transmissivity
of the plane glass 9 is substantially 100%.
In the example of FIG. 1, the QR half-mirror 2 and plane glass
9 are maintained at an angle of 90 degrees to each other by the
mirror holder 8a and plane glass holder 8b. Attached to the mirror
holder 8a is an extension spring 10 which urges the mirror holder
8a and QR half-mirror 2 around the axis of rotation 12 in a clockwise
direction which is the direction of retraction from the imaging
optical path.
During observation, the QR half-mirror 2 is kept at 45 degrees
to the main optical axis against the urging of the extension spring
10 by an L-shaped retaining lever 11. The retaining lever 11 has
a groove 11b at the end of its horizontal arm to engage with a pin
8c provided on the mirror guide lever 8. The retaining lever 11
can rotate about an axis of rotation 11a in the bend between the
two arms of the L shape. The retaining lever 11 is maintained during
observation in the position indicated in the drawing by a solid
line using a solenoid or other such mechanical means, which are
connected with a release button (not shown) for triggering to perform
imaging. Thus, during observation, the QR half-mirror 2 is maintained
at 45 degrees to the main axis.
When an imaging operation is initiated by the user, the retaining
lever 11 is released. This allows the mirror guide lever 8 to be
rotated clockwise by the force of the extension spring 10, moving
the mirror holder 8a and QR half-mirror 2 to the respective positions
indicated by the dotted lines. As described, the QR half-mirror
2 and plane glass 9 are maintained at 90 degrees to each other by
the mirror holders 8a and 8b, so the movement of the QR half-mirror
2 to the horizontal position shown by the dotted line causes the
plane glass 9 to move into a position in front of the imaging element
3 where it forms an angle of 90 degrees with respect to the optical
axis of the group of objective lenses 1. The plane glass 9 (QR half-mirror
2) moves until the plane glass holder 8b is stopped by engagement
with a stop 15. In this way, all of the light transmitted by the
group of objective lenses 1 reaches the imaging element 3, so that
the optical image of the subject falls incident on the imaging element
3 without loss of light due to the QR half-mirror 2.
A CCD driver 13 drives the imaging element 3, whose output is input
to a controller 14 composed of a microprocessor, memory and other
such components. Image data received from the imaging element 3
during the imaging is stored on a memory card or other such recording
medium (not shown) by the controller 14. In this embodiment, during
observation the light from the subject is able to enter the imaging
element 3 via the QR half-mirror 2. Therefore, the image data thus
obtained from the imaging element 3 during observation can be processed
for display on a monitor (not shown), processed for automatic focusing
by using the AF motor 16 to control the movable focusing lens group
1b, or used for calculations for controlling exposures, and so forth.
A CCD or other such device can be used for the imaging element
3. However, devices such as CCDs are often sensitive to infrared
light, and aberration from infrared regions can have an adverse
effect on image quality, exposure control and automatic focusing
control and the like. Taking that into consideration, it is preferable
to provide the downstream side of the plane glass 9 and/or the QR
half-mirror 2 with a coating or the other such means that filters
out infrared light. Providing the plane glass 9 with IR-blocking
filter characteristics will eliminate infrared light when the plane
glass 9 is inserted during imaging, thereby preventing degradation
of the image quality. Moreover, the rear surface of the QR half-mirror
2 (the imaging element side) can be provided with a coating that
blocks infrared. This assures the precise control of exposure and
automatic focus control using the imaging element 3.
If infrared light only needs to be blocked during imaging, infrared-blocking
properties only need to be imparted to the plane glass 9. When infrared
blocking is required during both imaging and observation, the QR
half-mirror 2 and the plane glass 9 are both given infrared-blocking
characteristics. Only the QR half-mirror 2 needs to be given infrared-blocking
properties if such characteristics are only required during observation.
Normally the light beam is allowed to enter the observation optical
system without infrared filtering, in which case it is not necessary
for the QR half-mirror 2 to be provided with an infrared-blocking
coating.
Although optical filtering characteristics of the QR half-mirror
2 and plane glass 9 have been described with reference to blocking
infrared light, if desired a person skilled in the art can provide
the QR half-mirror 2 and plane glass 9 with low-pass or band-pass
or other such spatial frequency filter characteristics for adjusting
automatic focusing performance. Moreover, when the subject is underwater,
polarizing filter characteristics can be provided to remove the
effect of reflections from the water, or ND filter characteristics
or the like can be provided for adjusting the exposure gain. Providing
the QR half-mirror 2 and/or the plane glass 9 with prescribed filter
characteristics makes it possible to optimize the conditions for
imaging and observation, and for exposure and automatic focus control
prior to the imaging.
The operation of the terrestrial telescope with a digital camera
thus configured will now be described.
A user half-presses the release button (not shown) to switch the
system on when the QR half-mirror 2 is in the observation position
shown in FIG. 1. The controller 14 then detects the light from the
subject entering the imaging element 3 via the QR half-mirror 2
and performs photoelectrical conversion to detect the brightness
and the contrast by a conventional contrast detection method.
The controller 14 can then determine the electronic shutter speed
of the imaging element based on the detected brightness of the subject,
drive the AF motor 16 based on the detected contrast, and control
the automatic focusing process by moving the movable focusing lens
group 1b along the optical axis. That is, the controller 14 drives
the AF motor 16 to move the movable focusing lens group 1b to the
focus position at which the imaging element 3 can produce an image
with the optimum contrast.
The focus position is determined based on the photoelectrical output
of the subject image transmitted by the QR half-mirror 2 to fall
incident on the imaging element 3. When the QR half-mirror 2 is
retracted for imaging, the focus position will change unless the
plane glass 9 is inserted into position. In FIG. 2, it is assumed
that A is the position of an image formed by the light transmitted
by a QR half-mirror 2 having a thickness d, and B is the position
of the image when there is no QR half-mirror 2 or plane glass 9.
The image-formation position A will be further away from the QR
half-mirror 2 than image-formation position B because the refractive
index n of the QR half-mirror 2 is n>1 (refractive index n of
air is 1).
The image-formation positional deviation .delta. between when there
is a QR half-mirror 2 and when there is neither a QR half-mirror
2 nor a plane glass 9 can be geometrically expressed as shown in
Equation (1) in terms of movement of the image-formation position
along the optical axis by the central beam 10 and the peripheral
beam 11. ##EQU1##
Here, the glass (or whatever other material is used) of the QR
half-mirror 2 is assumed to have a refractive index of n, the angle
of incidence of the central beam 10 on the QR half-mirror 2 is assumed
to be 45 degrees, and the angle of incidence of the peripheral beam
11 on the QR half-mirror 2 is assumed to be .theta..
In this embodiment, the deviation between image-formation positions
A and B is corrected by means of the plane glass 9. When the release
button is fully depressed, the retaining lever 11 rotates counterclockwise,
allowing the QR half-mirror 2 to retract and the plane glass 9 to
descend into the optical axis until it engages with the stop 15.
FIG. 3 shows the plane glass 9 inserted into the main optical axis
during imaging, wherein it is assumed that the plane glass 9 is
inserted perpendicularly to the optical axis after the retraction
of the QR half-mirror 2. The deviation .delta. in the position of
the images formed by the central beam 10 and the peripheral beam
11 can be approximated as shown in Equation (2) with the refractive
index n' of the plane glass 9 and the thickness d' of the plane
glass 9.
Equation (2) is based on Snell's law. When the plane glass 9 is
inserted so that it intersects the optical axis at an angle of 90
degrees as shown in FIG. 3, Equation (2) teaches that the term relating
to the angle of incidence .theta.' of the peripheral beam 11 can
be neglected and the image deviation .delta. is determined by the
thickness d' and refractive index n' of the plane glass 9. It therefore
follows that the required thickness d' of the plane glass 9 can
be calculated by resolving the equations in respect of plane glass
thickness d' by substituting the right-side term of Equation (1)
for the left-side term of Equation (2) to equalize the amount of
image deviation .delta. of the left sides of Equations (1) and (2).
FIG. 4 shows the calculated values. Specifically, the table lists
the calculated values obtained using Equations (1) and (2) under
the condition that a QR half-mirror 2 has thickness d of 1 (mm)
and the QR half-mirror 2 and plane glass 9 have the same glass with
a refractive index n=n'=1.51633.
The results of FIG. 4 show that the amount of deviation .delta.
to be corrected is not constant, but depends on the angle of incidence
.theta. of the peripheral beam 11 shown in FIG. 2. If the QR half-mirror
2 is inserted at an angle of 45 degrees, the deviation .delta. increases
with the increase in the angle of incidence .theta. of the peripheral
beam 11. (There is a special case, which is when .theta. is 45 degrees
at which .delta.=infinite and there is no image formation.) Thus,
it can be said that coma aberration produced by the QR half-mirror
2 cannot be completely removed unless the thickness of the inserted
plane glass 9 is gradually changed. As can be seen from Equation
(2), the amount of axial deviation due to the correction glass is
not affected by .theta..
However, there is more emphasis on the central field of view than
on the peripheral in the actual optical system whether it is a case
of the contrast calculation area or the captured image. That is,
calculations are made with emphasis on the paraxial region of the
peripheral beam 11 (at an angle of incidence .theta. close to 45
degrees), so the calculated results of FIG. 4 are also employed
with respect to .theta.=45 degrees. This means that a plane glass
thickness d' of 1.77 mm is employed to eliminate image deviation.
The effect of inserting the plane glass 9 compared to not inserting
the plane glass 9 can be evaluated as follows.
With reference to FIG. 4, the amount of focal deviation (.delta.)
along the optical axis between when the QR half-mirror 2 is retracted
from the optical axis and when it is inserted is a maximum of 0.70
mm when there is no plane glass 9. Inserting a plane glass 9 having
a thickness of 1.77 mm corrects the deviation at the center of the
viewing angle, so the range of deviation is 0.70-0.60=0.10 mm.
If the QR half-mirror 2 is retracted and no correction is made,
such as by the insertion of the plane glass 9 in the case of the
example of this embodiment, then the camera is, for example, operated
using the automatic focus control conditions calculated with the
QR half-mirror 2 in the non-retracted position. This will degrade
the image quality. The degree of degradation vary depending on various
factors such as the depth of field (stop) during the image pickup,
so that the degradation will be severe if the depth of field is
kept shallow.
In accordance with this embodiment, the deviation from the image-formation
position when the QR half-mirror 2 was in the inserted position
can be corrected by inserting the plane glass 9. Therefore, even
if the system is operated using the automatic focusing control conditions
calculated with the QR half-mirror 2 in the inserted position, the
degree of image degradation will be reduced. In particular, in accordance
with this embodiment the plane glass 9 is inserted perpendicularly
to the optical axis. This causes the effect of the plane glass 9
for correcting the image-formation position to act equally with
respect to imaging light rays in various directions (refer to the
non-dependence on angle of incidence .theta.' of the peripheral
beam in Equation (2)), and as shown in FIG. 4, during imaging there
is no image degradation caused by image-formation positional deviation
arising from a dependency on the direction of the peripheral light
involved in the image formation.
Thus, the use of the plane glass 9 makes it possible in accordance
with the embodiment to correct changes in the image-formation position
arising from the retraction of the QR half-mirror 2 from the optical
axis. After inserting the plane glass 9, the imaging element 3 images
the subject for the exposure time, which is determined when the
release button was half-pressed. When the imaging is completed,
the controller 14 operates a drive motor (not shown) to return the
QR half-mirror 2 and plane glass 9 to the standby position.
The terrestrial telescope with a digital camera according to the
invention employs an optical-path-splitting means in the form of
a half-mirror that is used to direct light from the subject to both
the imaging element and the observation optical system. During imaging
the half-mirror is removed from the main optical system, and an
optical element (the plane glass 9) is inserted into the main optical
system to correct for any deviation in the image-formation position
caused by the retraction of the half-mirror. Therefore, there is
no loss of incident light to the imaging element during the imaging.
Moreover, no processor or memory has to be used, and the plane glass
9 used for the positional correction is a simple optical element,
enabling deviation of the focus position to be corrected using a
configuration that is very simple and low-cost. Since a half-mirror
is used to split the optical path, the imaging element can be used
during observation to acquire imaging data for various purposes
such as exposure adjustments, monitor display and automatic focus
adjustments.
Moreover, the plane glass 9 and the QR half-mirror 2 constituting
the optical-path-splitting means are not maintained on separate
levers but on the ends of a single, rigid mirror guide lever 8,
which is used to position the QR half-mirror 2 and plane glass 9.
This reduces the number of parts and enables the apparatus to be
achieved easily and at a low cost. Also, there is very little error
in the positioning of the QR half-mirror 2 and plane glass 9, ensuring
precise correction of the image-formation position.
To facilitate the above explanation, the QR half-mirror 2 and plane
glass 9 were described as being inserted into the main optical system
at an angle of 45 degrees and 90 degrees respectively. However,
it is to be understood that the invention is not limited to these
conditions. Instead, the angles at which these members are disposed
relative to the main optical system, as well as other design conditions,
can be suitably modified as required. This also applies to the angle
between the QR half-mirror 2 and the plane glass 9, which was described
as being 90 degrees. If required by the drive configuration, installation
space or other such factors, the two members can be set at a different
angle.
As described in the foregoing, a terrestrial telescope with a digital
camera according to the invention employs an optical element that
is inserted into the optical axis of the imaging optical system
to correct for any change in image-formation position when the optical-path-splitting
means is retracted from the optical path of the imaging optical
system during imaging. Imaging can therefore be continuously performed
with no loss of light, and the focus position of the imaging element
can be corrected by means of a configuration that is simple and
low in cost, having no need for calculation means or means for driving
and controlling the optical element.
In particular, the optical element is a plane glass element having
a thickness that corrects for the change in the image-formation
position produced by the retraction of the optical-path-splitting
means. This allows deviation in the focus position to be corrected
with a straightforward, low-cost apparatus with a simple optical
element.
The retraction of the optical-path-splitting means and the insertion
of the optical element are controlled by means of a guide lever
member that supports the imaging position correction means on one
end and the optical-path-splitting means on the other end. Such
a configuration uses few parts and is therefore simple and low-cost,
but fully able to precisely correct the image-formation position.
Prescribed optical filtering properties can be imparted to the
optical element and to the exit side of the imaging element of the
optical-path-splitting means. This makes it possible to optimize
the conditions for imaging, observation, pre-imaging exposure control
and automatic focusing control.
Also, a configuration is used in which the plane glass is inserted
perpendicularly to the optical axis of the imaging optical system.
Such a configuration allows the corrective effect of the plane glass
to be applied equally with respect to imaging light from any direction.
It also serves to help optimize the automatic focusing control conditions
and prevents degradation of the acquired image.
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