U.S. patent application number 09/083963 was filed with the patent office on 2001-12-27 for indicator for an optical instrument.
Invention is credited to SUZUKI, SHINICHI.
Application Number | 20010055110 09/083963 |
Document ID | / |
Family ID | 15114365 |
Filed Date | 2001-12-27 |
United States Patent
Application |
20010055110 |
Kind Code |
A1 |
SUZUKI, SHINICHI |
December 27, 2001 |
INDICATOR FOR AN OPTICAL INSTRUMENT
Abstract
An indicator for an optical instrument including an
observational optical system to observe an image formed by an
objective optical system having a focusing lens group, comprising a
lens position detecting device to detect a position of the focusing
lens group, a distance detecting device to obtain an object
distance according to a position of the focusing lens group
detected by the lens position detecting device, and a display
device to display an object distance detected by the distance
detecting device.
Inventors: |
SUZUKI, SHINICHI; (SAITAMA,
JP) |
Correspondence
Address: |
GREENBLUM & BERNSTEIN
1941 ROLAND CLARKE PLACE
RESTON
VA
20191
|
Family ID: |
15114365 |
Appl. No.: |
09/083963 |
Filed: |
May 26, 1998 |
Current U.S.
Class: |
356/4.01 ;
396/139; 396/89 |
Current CPC
Class: |
G01C 1/02 20130101; G02B
23/10 20130101 |
Class at
Publication: |
356/4.01 ;
396/89; 396/139 |
International
Class: |
G01C 003/08; G03B
003/00; G03B 013/18; G03B 013/32; G03B 013/20 |
Foreign Application Data
Date |
Code |
Application Number |
May 23, 1997 |
JP |
9-133844 |
Claims
What is claimed is:
1. An indicator for an optical instrument including an
observational optical system to observe an image formed by an
objective optical system having a focusing lens group, comprising:
a lens position detecting device to detect a position of said
focusing lens group; a distance detecting device to obtain an
object distance according to a position of said focusing lens group
detected by said lens position detecting device; and a display
device to display an object distance detected by said distance
detecting device.
2. An indicator for an optical instrument according to claim 1,
wherein said display device is an inside-visual-field display
device which displays information of said object distance in a
visual field of said observational optical system.
3. An indicator for an optical instrument according to claim 1,
wherein said optical instrument is a telescope comprising, in order
from the object side, a fixed objective lens group, a movable
focusing lens group, an erecting optical system and an eyepiece
lens group.
4. An indicator for an optical instrument according to claim 1,
wherein said optical instrument is a collimating telescope of an
auto-level comprising, in order from the object side, a fixed
objective lens group, a movable focusing lens group, a horizontal
compensation optical system, a focusing plate and an eyepiece lens
group.
5. An indicator for an optical instrument according to claim 4,
wherein a display of said display device is provided in the
periphery of said focusing plate.
6. An indicator for an optical instrument according to claim 5,
wherein said optical instrument further comprises: a split optical
system between said horizontal compensation optical system and said
focusing plate; an AF sensor unit to detect a focusing state by
receiving light divided by reflection in said split optical system;
and a lens driving device to move said focusing lens group
according to a focusing state detected by said AF sensor unit.
7. An indicator for an optical instrument according to claim 6,
wherein said inside-visual-field display device further comprises a
projection optical system, which emits information of said object
distance on said spilt optical system, to project said information
of said object distance on the periphery of said focusing plate
through reflection by said split optical system.
8. An indicator for an optical instrument according to claim 6,
wherein said optical instrument further comprises a manual focusing
operation device which manually moves said focusing lens group.
9. An indicator for an optical instrument according to claim 8,
wherein said distance detecting device displays by said display
device through detecting said object distance when any operation to
move said focusing lens group is executed.
10. An indicator for an optical instrument according to claim 1,
wherein said distance detecting device calculates said object
distance according to a moving amount from a reference position of
said focusing lens group detected by said lens position detecting
device.
11. An indicator for an optical instrument according to claim 1
further comprising a memory, wherein said distance detecting device
selects said object distance from table data corresponding to a
position of said focusing lens group detected by said lens position
detecting device.
12. An indicator for an optical instrument according to claim 6,
further comprising an AF start switch, wherein said distance
detecting device is actuated, after said lens driving device is
stopped by operation of said AF start switch, to display a detected
object distance on said display device for a predetermined
time.
13. An indicator for an optical instrument including an
observational optical system to observe an image formed on a
predetermined focal plane by an objective optical system having a
focusing lens group, comprising: a split optical system positioned
between said objective optical system and said observational
optical system; a focusing detecting device to detect a defocus
amount at a position equivalent to said focal plane by receiving
light divided by said split optical system; a lens driving device
to drive said focusing lens group according to a defocus amount
detected by said focusing detecting device so that said defocus
amount becomes a smallest value; a lens position detecting device
to detect a position of said focusing lens group; an object
distance detecting device to obtain an object distance according to
a position of said focusing lens group detected by said lens
position detecting device and according to said defocus amount; and
a display device to display an object distance detected by said
object distance detecting device.
14. An indicator for an optical instrument according to claim 13,
wherein said display device is an inside-visual-field display
device which displays information of said object distance in a
visual field of said observational optical system.
15. An indicator for an optical instrument according to claim 13,
wherein said lens driving device stops movement of said focusing
lens group when an absolute value of defocus amount detected by
said focusing detecting device becomes smaller than a predetermined
value.
16. An indicator for an optical instrument according to claim 15,
wherein said object distance detecting device lo obtains an object
distance as an average of plural times of calculation of defocus
amount via said focusing detecting device, after said lens driving
device stops movement of said focusing lens group.
17. An indicator for an optical instrument according to claim 13,
wherein said display device displays, other than said object
distance information, at least one from among the following
information: focused/out-of-focus, the defocus direction, or the
amount-of-defocus.
18. An indicator for an optical instrument according to claim 13,
wherein said optical instrument is a telescope comprising, in an
order from the object side, a fixed objective lens group, a movable
focusing lens group, an erecting optical system and an eyepiece
lens group.
19. An indicator for an optical instrument according to claim 13,
wherein said optical instrument is a collimating telescope of an
auto-level comprising, in an order from the object side, a fixed
objective lens group, a movable focusing lens group, a horizontal
compensation and erecting optical system, a split optical system, a
focusing plate and an eyepiece lens group.
20. An indicator for an optical instrument according to claim 19,
wherein said inside-visual-field display device further comprises a
display in the periphery of said focusing plate.
21. An indicator for an optical instrument according to claim 19,
wherein said inside-visual-field display device further comprises a
projection optical system, which emits information of said object
distance on said spilt optical system, to project said information
of said object distance on the periphery of said focusing plate
through reflection by said split optical system.
22. An indicator for an optical instrument according to claim 13,
wherein said optical instrument further comprises a manual focusing
operation device which allows said focusing lens group to be
manually adjusted.
23. An indicator for an optical instrument according to claim 13,
wherein said distance detecting device displays said object
distance via said display device by detecting said object distance
when any operation to move said focusing lens group is
executed.
24. An indicator for an optical instrument according to claim 13,
wherein said distance detecting device calculates said object
distance according to a moving amount from a reference position of
said focusing lens group detected by said lens position detecting
device and according to said defocus amount.
25. An indicator for an optical instrument according to claim 13,
further comprising an AF start switch, wherein said distance
detecting device is actuated, after said lens lo driving device is
stopped via the operation of said AF start switch, to display a
detected object distance on said display device for a predetermined
time.
26. An optical apparatus for a surveying instrument comprising: a
telescopic optical system comprising: an objective lens group; a
focusing lens group; a focusing plate; an eyepiece lens group for
viewing images of objects formed on said focusing plate via said
objective lens group and said focusing lens group; a lens position
detecting device which detects the amount of movement of said
focusing lens group from a predetermined reference position; an
object distance detecting device which detects the object distance
with respect to the position of said focusing lens group according
to the detected said amount of movement via said lens position
detecting device; a display device for displaying the detected
object distance according to said object distance detecting
device.
27. An optical apparatus for a surveying instrument according to
claim 26, wherein said object distance detecting device calculates
the object distance based on: the amount of movement of said
focusing lens group obtained from said lens position detecting
device, the previously determined focal length of said objective
lens group, the focal length of said focusing lens group, and the
distance between said objective lens group and the focusing lens
group at the reference position.
28. An optical apparatus for a surveying instrument according to
claim 26, wherein said optical apparatus further comprises a memory
for storing table data on the relationship between the amount of
movement of said focusing lens group from said reference position
and the object distance; said object distance detecting device
detects said object distance by selecting from said memory the
object distance corresponding to said amount of movement based on
the amount of movement of said focusing lens group detected by said
lens position detecting device.
29. An optical apparatus for a surveying instrument according to
claim 26, wherein said optical apparatus further comprises: a beam
splitting optical system located between said focusing lens group
and said focusing plate; a focus detecting device, which receives a
spit beam which has been split by said beam splitting optical
system, for detecting the amount of defocus of an object at a
position equivalent to the position of said focusing plate; said
object distance detecting device detects the corrected object
distance by incorporating an average of a plurality of defocus
amounts obtained by said focus detecting device.
30. An optical apparatus for a surveying instrument according to
claim 26, wherein said optical apparatus further comprises: a beam
splitting optical system located between said focusing lens group
and said focusing plate; a focus detecting device, which receives a
spit beam which has been split by said beam splitting optical
system, for detecting the defocus direction and amount of defocus
of an object at a position equivalent to the position of the
focusing plate; said display device displays, in addition to the
object distance, at least one of the following:
focused/out-of-focus, the defocus direction, or the
amount-of-defocus.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an indicator for an optical
instrument, for example, an indicator applied to a surveying
instrument such as an auto-level or a transit instrument having a
telephotographic system.
[0003] 2. Description of the Related Art
[0004] A surveying instrument such as an auto-level or a transit
instrument is basically provided with a collimating telescope, a
level, and scales for measuring a rotative angle (an azimuth angle)
or an elevational angle. A typical auto-level collimating telescope
is provided, in order from an object side, with an objective lens
group, a focusing lens group, a horizontal compensation and
erecting optical system, and an eyepiece lens group. The position
of the focusing lens is adjusted according to the distance from the
object, so that an image of the object may be formed on a reticle
(focusing plate). The operator may thus observe the image
superimposed on the reticle via the eyepiece.
[0005] Surveying instruments, such as an auto-level, did not have a
distance measuring apparatus that could indicate the distance to an
object, for example to a staff. In particular, although the
auto-level may preferably be located at the equal distance position
from two measuring points, the auto-level has no function to
measure the distance. Therefore in the prior art, the position of
the auto-level has usually been decided according to experience and
intuition of the operator. Accordingly, it would be convenient if
the distance to the measuring point could be made known to the
operator.
[0006] A collimating telescope of surveying instrument in which an
automatic focusing apparatus is provided is well known. According
to a conventional automatic focusing apparatus, even if accurate
focusing is not carried out, as long as the defocus is little
enough so that the operator may feel as though the image is
focused, the focusing operation would be stopped. However, the
measuring of the object distance with the existence of such a
defocus may result in a large object distance error.
SUMMARY OF THE INVENTION
[0007] It is an object of the present invention to provide an
indicator of an optical instrument to carry out focusing by moving
a focusing lens group, in which an object distance observed by an
operator can be indicated to the operator.
[0008] It is another object of the present invention to provide an
automatic focusing apparatus which can detect the object distance
more accurately.
[0009] Since the distance of an object being viewed through a
survey instrument having a collimating telescope is conventionally
determined as being the distance from the objective lens group of
the collimating telescope to the focusing plate, if the focal
length of the objective lens group and the focusing lens group, and
the distance between the objective lens group and the focusing lens
group are known, the object d-stance can be readily determined.
Namely, if the amount of movement of the focusing lens group from a
reference position (for example, the position of a focusing lens
group in infinity) is detected, the distance to the object can be
obtained. Therefore, to achieve the object mentioned above,
according to the present invention, there is provided an indicator
for an optical instrument including an observational optical system
to observe an image formed by an objective optical system having a
focusing lens group, composing of: a lens position detecting device
to detect a position of the focusing lens group, a distance
detecting device to obtain an object distance according to a
position of the focusing lens group detected by the lens position
detecting device, and an inside-visual-field display device to
display an object distance in a visual field of the observational
optical system detected by the distance detecting device.
[0010] Further, according to an invention as claimed in claim 13,
there is provided an indicator for an optical instrument including
an observational optical system to observe an image formed on a
predetermined focal plane by an objective optical system having a
focusing lens group, composing of: a split optical system
positioned between the objective optical system and the
observational optical system, a focusing detecting device to detect
a defocus amount at a position equivalent to the focal plane by
receiving light divided by the split optical system, a lens driving
device to drive the focusing lens group according to a defocus
amount detected by the focusing detecting device so that the
defocus amount becomes a smallest value, a lens position detecting
device to detect a position of the focusing lens group; an object
distance detecting device to detect an object distance according to
a position of the focusing lens group detected by the lens position
detecting device and according to the defocus amount; and an
inside-visual-field display device to display an object distance in
a visual field of the observational optical system detected by the
object distance detecting device.
[0011] The present disclosure relates to subject matter contained
in Japanese Patent Application No. 09-133844 (filed on May 23,
1997) which is expressly incorporated herein by reference in its
entirety.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The invention will be described below in detail with
reference to the accompanying drawings, in which:
[0013] FIG. 1 is a block diagram of main elements of an embodiment
of an auto-level to which the present invention is applied;
[0014] FIG. 2 is a view of an embodiment of the visual field
according to the present invention;
[0015] FIG. 3 is a block diagram of main elements of another aspect
of an auto-level to which the present invention is applied;
[0016] FIG. 4 is a view showing a mechanism of obtaining an object
distance according to the embodiment of the present invention;
[0017] FIG. 5 is a flow chart showing a partial operation (START)
in an automatic focusing operation of an auto-level according to
the present invention;
[0018] FIG. 6 is a flow chart showing a partial operation (VDD
LOOP) in the automatic focusing operation of the auto-level
according to the present invention;
[0019] FIG. 7 is a flow chart showing a partial operation (AF
OPERATION) in the automatic focusing operation of the auto-level
according to the present invention;
[0020] FIG. 8 is a flow chart showing a partial operation (PULSE
CALCULATION) in the automatic focusing operation of the auto-level
according to the present invention;
[0021] FIG. 9 is a flow chart showing a partial operation (DRIVE
DIRECTION CHECK) in the automatic focusing operation of the
auto-level according to the present invention;
[0022] FIG. 10 is a flow chart showing a distance indication
operation of the auto-level according to the present invention;
and
[0023] FIG. 11 is a flow chart showing the other distance
indication operation of the auto-level according to the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] The present invention will now be described in detail with
reference to drawings attached hereto. FIG. 1 shows an embodiment
of an auto-level to which an automatic focusing apparatus according
to the present invention is applied. An auto-level 10 consists of a
collimating objective lens group 11 of positive power and a
focusing lens group 12 of negative power which serve as the
objective optical system, an optical horizontal compensation system
13, a spilt optical system (divided optical system) 16, a first
focusing plate 14a and a second focusing plate 14b to integrally
serve as a focusing plate (reticle) 14, and an eyepiece lens group
15 of positive power (observational optical system), in this order
from the object side (left side of FIG. 1).
[0025] The optical horizontal compensation system 13, per se known,
consists of a first compensation prism 13a, a compensation mirror
13b, and a second compensation prism 13c, and has a symmetrical
shape. The optical horizontal compensation system 13 is hung from a
shaft by a string or the like (not shown). The angle defined
between the compensation mirror 13b and the first compensation
prism 13a is identical (in absolute-value) to the angle defined
between the compensation mirror 13b and the second compensation
prism 13c, but are opposite in direction. The angle, for example
30.degree. varies depending on the length of the string, etc. When
the optical horizontal compensation system 13 is set so that the
optical axes of the objective lens group 11 and the focusing lens
group 12 are substantially parallel (inclined at, for example,
about 10 to 15 minutes with respect to the horizontal axis), light
incident upon the first compensation prism 13a is deviated from the
horizontal direction by the same amount, but the light reflected by
and emitted from the first compensation prism 13a, the compensation
mirror 13b and the second compensation mirror 13c, is substantially
collimated.
[0026] The focusing lens group 12 is provided with a rack 12a
secured thereto, which is engaged by a pinion 12b. When a rotation
of the pinion 12b takes place to move the focusing lens group 12 in
the optical axis direction, the image of an object 9 formed by the
objective lens group 11 and the focusing lens group 12 is
translated along the optical axis. The operator views the object
image formed on the focusing plate 14 together with the reticle
etc., drawn on the focusing plate 14, through the eyepiece 15.
[0027] There is an indicator 17 provided under the focusing plate
14. The embodiment shown in FIG. 2 is the indicator 17 which
indicates not only the distance information to the object 9, but
also whether or not the focusing is completed, and whether the
current focusing state is in auto-mode (AF) or manual-mode
(MF).
[0028] A beam splitter (half mirror) 16 is provided in the light
path between the objective lens group 11 and the focusing plate 14
to split the light (or light path). A focus detecting system (focus
detector) 20 is provided in the split light path to detect the
focus state (state of the formed image) at an equivalent surface
14A which is optically equivalent to the focusing plate 14. The
focusing lens 12 is driven by a lens driver (focusing lens group
driving system) 30 in accordance with she output of the focus
detector 20.
[0029] The focus detector 20 includes an AF sensor 21 located in
the vicinity of the equivalent surface 14A, so that the defocus
amount (defocus, front focus, rear focus) can be detected in
accordance with the output of the AF sensor 21, of which structure
is known per se. The AF sensor in the present embodiment is a phase
matching type, in which the object image on the equivalent surface
14A is split by a condenser lens and a pair of separator lenses
(image forming lenses) spaced at a distance identical to the base
length, and is re-formed on a pair of CCD line sensors. The CCD
line sensors are each provided with a number of photoelectric
transducers which convert the object image received into electrical
charges which are integrated (accumulated). The integrated charges
are successively output as AF sensor data. The AF sensor data is
amplified by a preamplifier 22 before being supplied to the
calculation/control circuit 23. The calculation/control circuit 23
calculates the defocus amount through a predetermined defocus
calculation in accordance with the AF sensor data. In the
illustrated embodiment, in addition to the defocus amount, the
displacement and direction of the movement of an AF motor 31 (the
number of output pulses, referred to hereinafter as "AF pulses" of
an encoder 33) necessary to move the focusing lens 12 until the
defocus amount becomes zero is also calculated in accordance with
the defocus amount. The number of AF purses is set in an AF pulse
counter 23a incorporated in the calculation/control circuit 23.
[0030] The calculation/control circuit 23 drives the AF motor 31
through an AF motor drive circuit 25, in accordance with the
rotational direction of the AF motor 31, in order to be decrement
the AF pulse counter 23a by detecting the output from the encoder
33. The rotation of the AF motor 31 is transmitted to the pinion
12b through a clutch-incorporated reduction mechanism 32 to move
the rack 12a (namely, the focusing lens group 12). The
calculation/control circuit 23 also controls the driving speed and
stopping of the AF motor 31 based on the amount counted by the AF
pulse counter 23a. Namely, when the counted amount is larger than a
predetermined amount, the driving speed becomes high, and when the
counted amount is smaller than the predetermined amount, the
driving speed becomes low to allow braking, etc.
[0031] The calculation/control circuit 23 detects the defocus
amount (i.e. detects focusing) against the object 9 by device of
the focus detector 20 and the lens driver 30, in order to move the
focusing lens group 12 in the optical axis direction. Accordingly,
when the absolute amount of defocus is smaller than the
predetermined amount, the lens driver 30 stops at that point, being
determined as in-focus. Thus the focusing is essentially completed
with respect to the object 9.
[0032] The focusing lens group 12 (rack 12a) is provided with a
movement detector 19 to detect the moving amount of the focusing
lens group 12 from an infinity focal position. The distance to the
object 9 in a focused state is uniformly defined according to the
focal lengths of the objective lens group 11 and the focusing lens
group 12, the distance between the objective lens group 11 and the
focusing plate 14, and the distance between the objective lens
group 11 and the focusing lens group 12. Accordingly, when the
moving amount of the focusing lens group 12 is detected by the
movement detector 19, the distance to the object 9 may be obtained.
Thus the calculation/control circuit 23 obtains the object distance
based on the amount of movement of the focusing lens group 12
detected by the movement detector 19, and indicates the obtained
object distance on the indicator 17.
[0033] The movement detector 19 may include, for example, a
code-plate/brush mechanism known per se, to detect the absolute
position of the focusing lens group 12. The movement detector 19
may also include, for example, an optical encoder which detects the
relative position of the focusing lens group 12, namely the moving
amount from the reference position (infinity focal position).
[0034] The focus detector 20 is provided with an AF start switch 27
to start the automatic focusing operation, a focusing operation
knob 34 to change modes of focusing, and an AF switch 29 which
detects the AF mode (that is, the mode which is not the manual
focus mode).
[0035] The pinion 12b is driven in either a manual focus mode by
the focusing operation knob 34, or in an autofocus mode, in which
the automatic focusing operation is carried out in accordance with
the focus detector 20 and the lens driver 30. Namely, the
auto-level 10 is constructed such that the focusing mode is
switched between the autofocus mode, in which the focusing lens
group 12 is driven in accordance with the output of the focus
detector 20, and the manual focus mode, in which the focusing lens
group 12 is driven manually regardless of the output of the focus
detector 20.
[0036] For instance, when the focusing operation knob 34, which
constitutes a mode switching device between the manual focus mode
and the autofocus mode, is moved in one axial direction, the manual
mode is obtained, and when the focusing operation knob 34 is moved
in another axial direction, an autofocus mode (AF mode) is
obtained. For example, when the focusing operation knob 34 is
switched to the manual focus mode, the clutch-incorporated
reduction mechanism 32 disconnects the AF motor 31 from the
reduction mechanism 32, and when the focusing operation knob 34 is
switched to the autofocus mode, the clutch-incorporated reduction
mechanism 32 clutches the AF motor 31 with the reduction mechanism
32. The clutch-incorporated reduction mechanism 32 may either be
constructed so as to maintain connection with the focusing
operation knob 34 at all times regardless of position (mode) of the
focusing operation knob 34, or be constructed so as to disconnect
from the focusing operation knob 34 when switched to the autofocus
mode. The calculation/control circuit 23 detects whether the
focusing operation knob 34 is switched to the autofocus mode when
the AF switch 29 is turned OFF.
[0037] FIG. 3 shows another aspect according to the embodiment of
the present invention, wherein the auto-level 10 according to the
embodiment of FIG. 1 has an indication projector 172 above the beam
splitter 16, instead of the indicator 17, to project the indication
data such as distance information. The indication light projected
from the indication projector 172 is incident on the beam splitter
16 through a projection lens 173. The light is then reflected
toward the focusing plate 14 at a surface of the beam splitter 16
on which the split light is reflected, so that the light may be
incident on the lower portion of the focusing plate 14. Since the
projection lens 173 is adjusted to be focused on the focusing plate
14, the lower portion of the focusing plate 14 indicates, the
object distance, whether AF or MF, and whether focused or not
focused, as shown in FIG. 2. The projection of the distance
information by the indication projector 172 is controlled by the
calculation/control circuit 23.
[0038] There is an example of operation for obtaining the object
distance from the position of the focusing lens group 12 with
reference to FIG. 4. The lens system is an inner focus lens which
forms an image on a focusing surface P at a fixed position, by a
fixed objective lens group L1 and a movable focusing lens group L2,
likewise the case of the collimating telescope as shown in FIG. 1.
Marks G1 and G2 respectively correspond to principal points of the
objective lens group L1 and the focusing lens group L2.
[0039] The following formulas may be obtained wherein: f1 is the
focal length of the objective lens group L1, f2 is the focal length
of the focusing lens group L2, L is the distance from the principal
point G1 (of the objective lens group L1) to the focusing surface
p, a is the distance from the principal point G1 to the object 9
(hereinafter "object distance"), b is the distance from the
principal point G1 to an image point I1 of the object 9 formed by
the objective lens group L1, d is the distance between the
principal points G1 and G2, a' is the distance from the principal
point G2 (of the focusing lens group) to the focal point f1 of the
objective lens group L1, and b' is the distance from the principal
point G2 to the focusing surface p. In the following formulas, the
focal lengths f1 and f2, and the distance L from the principal
point G1 to the focusing surface p, are invariable values so long
as the image optical system is an inner focus type, and the lens
distance d+.DELTA.d is a variable number according to the object
distance a.
[0040] The formula relating to imaging of the objective lens
group:
1/(-a)+1/b=1/f1 (1)
[0041] The formula relating to imaging of the focusing lens
group:
1/(-a')+1/b'=1/f2 (2)
[0042] Wherein the distance L is constant, provided that b', when
a=.infin. is bm', according to the formula (2),
1/(-(f1-d))+1/bm'=1/f2
[0043] Therefore:
bm'=f2(f1-d)/(f1-d+f2) (3)
[0044] In which, when the principal point G2 (of the focusing lens
group L2) is moved by the amount of .DELTA.d,
b'=bm'-.DELTA.d (4)
[0045] The formula (2) may be modified as:
a'=f2.times.b'/(f2-b') (5)
[0046] Therefore, the distance d' between the principal points G1
and G2 can be obtained as follows:
d'=d+.DELTA.d (6)
[0047] Therefore, the distance "b" to the image point I1 of the
object 9 is obtained by:
b=d'+a' (7)
[0048] The formula (1) may be modified as:
a=f1.times.b/(f1-b) (8)
[0049] In the above formulas, the focal lengths f1 and f2 the
distances L from the principal point G1 to the focusing surface p,
and the distance d between the lenses, are fixed. Therefore, when
the moving amount of the lens .DELTA.d is measured, it is possible
to obtain the object distance "a" by applying the formulas (3)
through (8).
[0050] The above formulas relate to the operation to obtain the
object distance for an inner focus telephotographic optical system.
In the case of telephotographic system which moves the objective
lens group as a whole, the object distance "a" may be obtained
by:
1/f=1/a+1/b
[0051] wherein:
a=1/(1/f-1/b).
[0052] The above formulas are the examples to obtain the object
distance "a" by calculation. However, it is also possible to obtain
the distance by reading the object distance data corresponding to
table data. The table data is recorded in a memory (EEPROM 26) by
calculating the relation between the object distance "a" and the
moving amount .DELTA.d of the focusing lens group L2 in advance
through calculation of every predetermined step of the focusing
lens group L2 When the moving amount of focusing lens group L2 is
detected, the object distance data can be read corresponding to the
table data. Tables 1 and 2 show an example of the corresponding
relation, in which, f1=90.162 (mm), f2=-52.165 (mm), d=55.452 (mm).
In this case, if the object distance "a" corresponding to the
moving amount of focusing lens group L2 which has not been
processed as the table data is obtained by interpolation operation,
a more accurate object distance "a" may be obtained.
1 TABLE 1 .DELTA.d (Mm) b' a' d' b a(mm) 0.00 103.73 34.710 55.45
90.16 -.infin. 0.10 103.63 34.699 55.55 90.25 -91639 0.20 103.53
34.688 55.65 90.34 -45868 0.30 103.43 34.676 55.75 90.43 -30611
0.40 103.33 34.665 55.85 90.52 -22983 0.50 103.23 34.654 55.95
90.61 -18406 0.60 103.13 34.643 56.05 90.69 -15354 0.70 103.03
34.631 56.15 90.78 -13175 0.80 102.93 34.620 56.25 90.87 -11540
0.90 102.83 34.609 56.35 90.96 -10269 1.00 102.73 34.597 56.45
91.05 -9252 1.10 102.63 34.586 56.55 91.14 -8420 1.20 102.53 34.575
56.65 91.23 -7726 1.30 102.43 34.563 56.75 91.32 -7139 1.40 102.33
34.552 56.85 91.40 -6636 1.50 102.23 34.540 56.95 91.49 -6200 1.60
102.13 34.529 57.05 91.58 -5819 1.70 102.03 34.518 57.15 91.67
-5482 1.80 101.93 34.506 57.25 91.76 -5183 1.90 101.83 34.495 57.35
91.85 -4916 2.00 101.73 34.483 57.45 91.94 -4675 2.10 101.63 34.472
57.55 92.02 -4457 2.20 101.53 34.460 57.65 92.11 -4259 2.30 101.43
34.449 57.75 92.20 -4078 2.40 101.33 34.437 57.85 92.29 -3912 2.50
101.23 34.426 57.95 92.38 -3759 2.60 101.13 34.414 58.05 92.47
-3619 2.70 101.03 34.402 58.15 92.55 -3488 2.80 100.93 34.391 58.25
92.64 -3367 2.90 100.83 34.379 58.35 92.73 -3254 3.00 100.73 34.368
58.45 92.82 -3149
[0053]
2 TABLE 2 .DELTA.d (Mm) b' a' d' b a(mm) 0.094 103.64 34.699 55.55
90.25 -97482 0.098 103.63 34.699 55.55 90.25 -93507 0.100 103.63
34.699 55.55 90.25 -91639 0.102 103.63 34.699 55.55 90.25 -89844
0.106 103.63 34.698 55.56 90.26 -86457 0.194 103.54 34.688 55.65
90.33 -47284 0.198 103.53 34.688 55.65 90.34 -46331 0.200 103.53
34.688 55.65 90.34 -45868 0.202 103.53 34.687 55.65 90.34 -45415
0.206 103.53 34.687 55.66 90.34 -44535 0.494 103.24 34.655 55.95
90.60 -18628 0.498 103.23 34.654 55.95 90.60 -18479 0.500 103.23
34.654 55.95 90.61 -18406 0.502 103.23 34.654 55.95 90.61 -18333
0.506 103.23 34.653 55.96 90.61 -18189 0.919 102.81 34.606 56.37
90.98 -10059 0.923 102.81 34.606 56.38 90.98 -10015 0.925 102.81
34.606 56.38 90.98 -9994 0.927 102.81 34.606 56.38 90.98 -9973
0.931 102.80 34.605 56.38 90.99 -9930
[0054] The automatic focusing operation of the auto-level 10 is
discussed below with reference to the flow charts shown in FIGS. 5
through 11 In the present embodiment, the object distance is
indicated on the indicator 17 or by the indication projector 172 by
detecting the moving amount of the focusing lens group 12 at
predetermined intervals when the AF start switch 27 is turned ON,
regardless of the automatic focusing operation mode (AF mode) or
the manual focusing operation mode (MF mode).
[0055] The following flow charts are executed by the
calculation/control circuit 23 in a state that an unillustrated
battery is loaded in the auto-level 10.
[0056] When the battery (not illustrated) is loaded, an internal
RAM and input/output ports, are firstly initialized at step S101 to
subsequently enter the power-down operation at step S103.
Thereafter, no operation at steps S101 and S103 are performed
unless the battery is unloaded and is then reloaded.
[0057] The power-down operation corresponds to a stand-by operation
in which the power source is OFF (except to calculation/control
circuit 23 and the movement detector 19) while the AF start switch
27 is OFF to wait for the operation of the AF start switch 27. If
the AF start switch 27 is turned ON, the power source is turned ON
to perform the AF operation (automatic focusing operation).
[0058] When the power-down operation is completed, flags for the AF
operation are reset at step S105. In the illustrated embodiment,
there are several kinds of flags to be reset, including a focusing
flag which represents that a focused state is obtained, an AFNG
flag which represents that the automatic focusing operation cannot
be carried out, a re-integration flag which represents that the
integration operation is performed after the focused state has been
obtained, and a search/overlap flag which is adapted to
discriminate that the integral operation is performed during
movement of the focusing lens 12.
[0059] If the reset operation for the AF operation is completed, a
check is made to determine whether the AF start switch 27 is turned
ON (step S107). Since the AF start switch 27 is OFF at the initial
position in which no operation by the operator occurs, the "OFF"
data is written in the AF start switch memory (steps S107, NO;
S109). Thereafter, a check is made to determine whether the power
source is ON at step S113. Since the power source is OFF at the
initial position in which no power is supplied to each circuit
(step S113: NO), the control is returned to step S105 and the
operations at steps S107, S109 and S113 are repeated.
[0060] If the AF start switch 27 is turned ON at step S107, the
control proceeds to step S111 to check whether the AF start switch
memory is ON. When the AF start switch memory is OFF (the AF start
switch memory is OFF at the first time), the control proceeds to
step S119 to write "ON" data in the AF start switch memory, and to
start a power hold timer (steps S111, NO; S119). Thereafter, if the
AF switch 29 is turned ON (in the AF mode), the power source is
turned ON to supply power to the circuits in order to perform the
VDD loop operation (steps S121; S123, YES; S125). If the AF switch
29 is OFF, which corresponds to the manual focusing mode, the
control is returned to step S101 (S123, NO; S113).
[0061] Even in the manual mode, the power source is turned ON by
turning the AF start switch 27 ON, thereby the power is supplied to
each circuit until the time of the power hold timer is up. Thus the
distance is displayed on the indicator 17 or by the indication
projector 172.
[0062] In the VDD loop operation, the automatic focusing operation
is carried out to obtain a focused state while detecting the state
of the AF start switch 27, and if the focused state cannot be
obtained, the control is returned to step S113.
[0063] When the control enters the VDD loop operation, the state of
the AF switch 29 is input again (step S210), and the control will
be able to proceed provided that the AF switch 29 is ON. If the AF
switch 29 is OFF, which corresponds to the manual focus mode, the
control is returned to the power-down operation (steps S201; S203,
NO; S113). The following discussion will be given on the assumption
that the AF switch 29 is ON.
[0064] If the AF switch 29 is ON, the AF operation is performed to
detect the defocus amount and accordingly move the focusing lens
group 12 to a focal position (steps S203, YES; S205). While the AF
start switch 27 is maintained ON, a check is made to determine
whether the AF start switch memory is ON at step S211. Since the AF
start switch memory has been ON at step S119, the focusing flag and
the AFNG flag are checked (steps S207, YES; S211, YES; S215; S217)
Since the focusing flag and the AFNG flag are both cleared if no
focused state nor the impossibility of the focusing operation are
detected during the AF operation, the control is returned to step
S201 (steps S215, NO; S217, NO; S210). The operations at steps
S201, S203, S205, S207, S211, S215, and S217 are repeated until
either the focused state is obtained and the focusing flag is set
to "1", or the focused state cannot be obtained and the AFNG flag
is set to "1".
[0065] The focusing lens group 12 has been moved to the focal
position during the AF operation at step S205, and when the
focusing flag is set to "1", the control is returned to the
power-down operation (steps S215, YES; S113). If focusing cannot be
effected for some reason, for example, when the aiming object moves
or is too dark or is too low in contrast, the AFNG flag is set to
"1" to return the control to the power-down operation at step S101
(steps S217: YES, S113).
[0066] When the AF start switch 27 is turned OFF during the VDD
loop operation, the control proceeds from step S207 to step S209 to
write "OFF" in the AF start switch memory. The control then
proceeds to step S215 by jumping step S211 (steps S207: YES, S209,
S215).
[0067] Further, when the AF switch 29 is turned OFF during the VDD
loop operation, that is, when the focusing operation knob 34 is
switched to the manual focus position, the control is returned from
step S203 to step S101 to end the AF operation S203, NO; S113).
[0068] When the control is returned to the power-down operation
(step S113), a check is made to determine whether the power source
is turned ON at step S113. When the power source is OFF, the
control is returned to the step S105. When the power source is ON
and the power hold state is maintained,the control is returned to
step S107 (steps S113, YES; S115, YES; S107). When the power hold
state is released, the control is returned to step S105 by
executing the power-down operation (steps S115, NO; S117; S105).
The term "maintaining" of the power hold means that the power hold
timer has not lapsed.
[0069] The AF operation at step S205 will be described below in
detail with reference to the flow charts shown in FIGS. 7 through
9. When the control enters the AF operation, the overlap flag, the
search flag and the reintegration flag are checked (steps S301,
S303, S305). Since all the flags have been cleared at step S105 at
the first step, the AF sensor executes the integration and the
integration result is input as AF sensor data to calculate the
defocus amount (steps S301, NO; S303, NO; S305, NO; S307). As is
well known, in the calculation of the defocus amount, a correlation
ratio of the data of a pair of AF sensors is obtained, so that the
direction of defocus (front focus or rear focus) and the defocus
amount can be obtained in accordance with the correlation
ratio.
[0070] A check is made to determine whether the calculated result
is effective at step S309. If the contrast of the aiming object is
too low, or the aiming object is a repetitive pattern, or the
object brightness is too low, there is a possibility that the
calculation result is ineffective. An effective calculation result
is usually obtained, and hence the effective calculation result
will be discussed below first.
[0071] If the calculation result is effective, the focus check
operation is performed. If a focused state is obtained, the focus
flag is set to "1". If a focused state is not obtained, i.e., an
out-of-focus state, the focus flag is set to "0"(steps S309, YES;
S321). In the illustrated embodiment, when the defocus amount is
within a predetermined limit or allowance, it is considered that a
focused state is obtained. If the focused state is obtained at step
S323, the control is returned to the VDD loop operation to perform
the operations at step S207 and steps subsequent thereto (step
S323, YES). In the case of an out-of-focus state, the control
proceeds to the pulse calculation operation (step S323, NO).
[0072] In the pulse calculation operation as shown in FIG. 8, the
number of AF pulses are calculated based on the effective defocus
amount. In other words, the amount of drive of the AF motor 31 (the
number of AF pulses supplied from the encode 33) necessary to move
the focusing lens group 12 until the defocus amount is zero is
attained.
[0073] When the control enters the AF pulse calculation operation,
the drive direction of the AF motor 31 and the number of AF pulses
are calculated in accordance with the defocus amount (step S331).
The obtained AF pulse number is set in the AF pulse counter 23a and
the AF motor 31 is DC-driven and the pulse checking is carried out
(steps S333, S335). The value of the AF pulse counter 23 a is
decreased by one every tire one AF pulse is output from the encoder
33.
[0074] In the pulse check operation, the drive speed of the AF
motor 31 is controlled in accordance with the value of the AF pulse
counter 23a. Namely, when the counted number is larger than the
overlap-integration-prohibition-pulse-number, the AF motor 31 is
driven at a high speed to move the focusing lens 12 toward the
focal position within a short space of time and the overlap
integration is also effected. When the counted number is smaller
than the overlap-integration-prohibition-pulse-number, although the
AF motor 31 is still driven at high speed, the overlap integration
is prohibited. If the counted number is smaller than a constant
speed control start pulse number, the AF motor 31 is driven under
PWM (Pulse Width Modulation) at low speed to prevent the focusing
lens group 12 from moving beyond the focal position. When the
counted number is zero, the AF motor 31 is stopped.
[0075] When the control enters the pulse check operation, the value
of the AF pulse counter 23a is compared with the
overlap-integration-prohibition- -pulse-number (step S341). If the
counter value is larger than the
overlap-integration-prohibition-pulse-number, the control proceeds
to step S343 in which the overlap flag is set to "1". Thereafter,
the overlap integration begins, and the AF sensor data is input
from the AF sensor 21 to perform the amount-of-defocus calculation
(steps S341, NO; S343; S345). If an effective calculation result is
obtained, the control proceeds to the drive direction check
operation (step S347: YES), and if no effective calculation result
is obtained, the control is returned (step S347, NO).
[0076] In the drive direction check operation as shown in FIG. 9,
the AF pulse number is calculated and set in the counter, based on
the AF sensor data obtained by the integration during driving of
the AF motor 31. If the drive direction changes, the AF motor 31 is
braked and stopped. In the illustrated embodiment, the AF motor 31
is braked by the short-circuiting of the AF motor 31 at opposite
electrodes thereof.
[0077] When the control enters the drive direction check operation,
the overlap flag is set to "1", and the search flag is set to "0"
(step S361). Thereafter, the previous and present drive directions
of the focusing lens group 12 are compared in accordance with the
calculation result (step S363). When the directions are identical
with each other, the AF pulse number is calculated at an
intermediate point of the integration, so that the calculated value
is set by the counter (steps S363, YES; S365). Subsequently, the
control is returned. If the drive direction changes, the AF motor
31 is braked and stopped. Consequently, the overlap flag is set to
"0" and the re-integration flag is set to "1". Thereafter, the
control is returned to the VDD loop operation (steps S363, NO;
S367; S369; S371).
[0078] When the control is returned to the VDD loop operation, the
operations at step S207 and steps subsequent thereto are carried
out, and the control enters the AF operation again. If no change in
the drive direction occurs, the control proceeds to the pulse check
operation from step S301 since the overlap flag is set to "1". The
operations from step S341 to step S347 and the operations of the
drive direction check operation from step S361 to step S365 are
carried out and the control is returned to step S205 for the pulse
check operation. These operations are repeated until the counter
value is smaller than the
overlap-integration-prohibition-pulse-number.
[0079] In the above mentioned AF operation, usually the AF pulse
number necessary to move the focusing lens group 12 to the focal
position is decreased and becomes smaller than the
overlap-integration-prohibition-pu- lse-number. Thus, the control
proceeds from step S341 to step S349 of the pulse check
operation.
[0080] The operations from step S349 to step S355 stop the AF motor
31 upon completion of driving of the AF motor corresponding to the
calculated AF pulse number. At step S349, control does not proceed
until the AF pulse number is smaller than the constant speed
control start pulse number. If the AF pulse number is smaller than
the constant speed control start pulse number, the AF motor 31 is
driven at a low speed in accordance with the remaining AF pulse
number. When the AF pulse number is zero, the AF motor 31 is
stopped (steps S349, YES; S351; S353, NO). When the AF motor 31 is
stopped, the overlap flag is set to "0", and the re-integrat ion
flag is set to "1" (steps S353, YES; S355). Thereafter, the control
is returned to the VDD loop operation.
[0081] If the control proceeds to step S205 of the VDD loop
operation, the control then enters the re-integration operation at
step S305, since the overlap flag and the search flag are set to
"0" and the re-integration flag is set to "1". The same is true
when the drive direction changes at step S363.
[0082] In the re-integration operation, the defocus amount is
calculated and whether or not the telescope is focused is checked
in accordance with the defocus amount thus obtained. If a focused
state is obtained, the focusing flag is set to "1", and if a
focused state is not obtained, the AF pulse is calculated again to
move the focusing lens group 12.
[0083] If the control is returned to the VDD loop operation when
the focusing flag is set to "1", the control proceeds to the
power-down operation from step S215. Thus, the AF operation ends
and the control waits for the operation of the AF start switch
27.
[0084] The above describes the control when the focused state is
correctly obtained. In the case that it is difficult or impossible
to obtain a focused state for some reason, the control enters the
VDD loop operation and is returned to the power-down operation in
an out-of-focus state. This will be discussed below.
[0085] In the first AF operation, the integration starts, the AF
sensor data is input, and the defocus amount is calculated at step
S307 (steps S301, NO; S303, NO; S305, NO; S307). If it is
impossible to calculate the effective defocus amount for some
reason, for example, when the object contrast is too low, the
control proceeds to the search integration operation from step S309
(steps S309, NO; S311).
[0086] In the search integration operation, the integration and the
defocus calculation are carried out to obtain an effective defocus
amount while driving the AF motor 31 from a close focal position to
an infinity focal position. If no effective defocus amount is
obtained even by the search integration operation, the AFNG flag is
set to "1" and the control is returned and enters the power-down
operation at step S217.
[0087] When the control enters the search integration operation
(search operation), the AF motor 31 is firstly search-driven (in
the direction of the close focal position) and the search flag is
set to "1" to commence the integration by the AF sensor 21. When
the integration is completed, the integral value is input as the AF
sensor data to calculate the defocus amount by defocus calculation
(steps S311, S313, S315). If the effective defocus amount is
obtained, the control proceeds to the drive direction checking
operation (step S317, YES). If no effective defocus amount is
obtained, the control is returned to the VDD loop operation to
perform the operations at step S207 and steps subsequent thereto
(steps S317, NO; S319).
[0088] The AF motor search-driving operation refers to an operation
in which the AF motor 31 is first driven in the direction of the
close focal position and when the focusing lens 12 reaches and
stops at a movement extremity on the close distance side, the AF
motor 31 is driven in the reverse direction, i.e., in the direction
of the infinity focal position. When the focusing lens group 12
reaches and stops at a movement extremity on the infinity side, the
AF motor 31 is stopped. If an effective calculation result is
obtained during the search driving, the AF motor is driven in
accordance with the effective value of the defocus amount.
[0089] When the control enters the operation at step S205 of the
VDD loop operation, the overlap flag is cleared. Since the search
flag is set to "1", the control enters the search integration
operation at step S303 and the search integration operations at
step S313 and steps subsequent thereto are carried out. If no
effective calculation result is obtained when the focusing lens
group 12 reaches the infinity focal position, the control enters
the AFNG operation, in which the AFNG flag is set to "1".
Thereafter, the control is returned to the VDD loop operation and
enters the power-down operation at step S217 (steps S317, NO; S319,
YES; S391).
[0090] The above discussion has been directed to the case when no
effective calculation result is obtained from the beginning. Once
an effective calculation result is obtained, thereby the focusing
lens group 12 is moved but still no focused state is obtained, if
no effective calculation result is obtained by the re-integration
operation (steps S381; S383), the control proceeds to the AFNG
operation from step S385. The AFNG flag is set to "1" in the AFNG
operation and thereafter, the control is returned to the VDD loop
operation and enters the power-down operation at step S217 (S385,
NO; S391).
[0091] The interrupt operation, whereby the calculation/control
circuit 23 interrupts at regular intervals via a hard timer during
executing the above operations, will now be described with
reference to FIG. 10. Firstly, the moving amount data from the
reference position of the focusing lens group 12 detected by the
movement detector 19 (counter value) are input at step S401. The
amount-of-movement data is represented by .DELTA.d. The object
distance "a" is obtained by calculation based on the
amount-of-movement data (step S403). The obtained object distance
is displayed on the indicator 17 (step S405).
[0092] The state of the AF switch 29 is input at step S407. If the
AF switch 29 is OFF, namely the present state is not the AF mode,
the manual focus mode as well as the out-of-focus state are
displayed (steps S407; S409, NO; S411; S413). Then the control is
returned. If the AF switch 29 is ON, namely the present state is
the AF mode, the AF mode is displayed (steps S407; S409, YES;
S415). Thereafter, the focusing flag is checked. If the focusing
flag has been set to "1", the focused state is displayed (steps
S417, YES; S419). Conversely, if the focusing flag has been set to
"0", the out-of-focus state is displayed (steps S417, NO;
S421).
[0093] The above interrupt operation may display the object
distance currently focused, on the display 17 a in the visual field
of the indicator 17, both in the autofocus mode and the manual
focus mode.
[0094] As the operator has power of analysis and focus recognition
ability via his/her eye(s), when he/she observes an object through
the collimating telescope of the auto-level 10 wherein a little
defocus amount exists, he/she may feel that the image is focused
even though the telescope is not actually in the focused state.
Accordingly, even if accurate focusing is not actually carried out,
as long as the defocus amount is insignificant enough such that the
operator feels the image is focused, the focusing operation in the
automatic focusing is considered as being in a focused state. Thus
the time required for focusing can be reduced, and "hunting" of the
telescope can be prevented.
[0095] However, it is true that the error of the object distance
will become larger when the object distance is obtained based on
the position of the focusing lens group 12 in which, as discussed
above, a little amount of defocus exists.
[0096] Therefore, according to a second embodiment of the present
invention, an amount-of-defocus to be considered as being focused
in the automatic focusing operation is set within a predetermined
amount, and the object distance may be obtained with reference to
the amount-of-defocus.
[0097] FIG. 11 shows the second embodiment of the present
invention, which is illustrated by a flow chart of the distance
indication operation. This distance indication is actuated
according to the forced interruption at regular intervals by a
timer, similar to the distance indication operation shown in FIG.
10.
[0098] When the control enters this distance indication operation,
the number of calculations is firstly cleared at step S501. The
number of calculations relates to a counter which counts and
controls the number of calculations of the defocus amount. The lens
position counter value is then input from the movement detector 19,
and the AF sensor data is also input to calculate the defocus
amount (steps S503, S505).
[0099] Thereafter, the focusing flag is checked. If the focusing
flag has been set to "1", the number of 1 is added to the number of
calculations, and when the present value of the number of
calculations is not N, the control is returned to step 505 (steps
S507, YES; S508; S509, NO; S505) Accordingly, when the focused
state is obtained, the calculations of the defocus amount are
repeated several times to improve accuracy of calculation of the
defocus amount. When the defocus amounts are calculated N times,
the average of the calculated defocus amounts is obtained, and the
lens position data is amended, then the control proceeds to step
S515 (steps S509, YES; S511; S513; S515). If the telescope is in an
out-of-focus state, the control jumps from step 507 to step 515
(steps S507, NO; S515).
[0100] The object distance "a" is calculated at step 515 based on
the lens position counter value and the lens position amended data.
The calculated object distance "a" is then displayed in a visual
field of the indicator 17 or by the indication projector 172 (step
517).
[0101] Thereafter, the focusing flag is checked. In the focused
state, the focused state is displayed (steps S519, YES; S521), and
in the out-of-focus state, the out-of-focus state is displayed
(steps S519, NO; S523). Then the state of the AF switch 29 is input
at step 525. In the AF mode (AF switch 29 is ON), the AF mode is
displayed and the control is returned (steps S527, YES; S529). In
the manual focus mode, namely not in the AF mode (AF switch 29 is
OFF), the MF mode is displayed (steps S527, NO; S531). In the MF
mode, if the defocus amount is effective, the defocus direction and
The defocus amount are displayed, and the control is returned
(steps S533, YES; S535). If the defocus amount is not effective,
the control is returned by jumping step 535 (step 533, NO).
[0102] According to the second embodiment of the present invention,
the object distance is displayed by not only using the position of
the focusing lens group 12, but also using the defocus amount
detected by the AF sensor 21, thus an accurate object distance may
be detected and displayed.
[0103] In addition, according to an aspect of the present
embodiment, the defocus direction and the defocus amount are
displayed, it is possible to confirm whether the accurate focused
state is obtained, and in the case of an out-of-focus state, it is
possible to confirm whether the present state is front focus or
rear focus, as well as the amount of error thereof.
[0104] Although the distance information is displayed in the visual
field according to the above embodiments as above illustrated, the
display is not limited to be positioned in the visual field, and
may be positioned outside the optical instrument. In addition,
although the above embodiments are applied to an auto-level, the
present invention can be equally applied to other surveying
instruments, such as a transit or a total station, as well as a
telescopic optical system such as a telescope or a binocular
telescope, etc.
[0105] As may be understood from the foregoing, according to the
present invention, the object distance is indicated in the visual
field of observation, by obtaining the object distance from the
position of the focusing lens group, in regard to the optical
instrument in which the focusing is carried out by moving the
focusing lens group. Thus the operator can easily confirm the
object distance during observing the object.
[0106] Further, according to the present invention as claimed in
claim 13 below, there is a device to detect the defocus amount, and
the position of the focusing lens group is amended according to the
defocus amount detected by the defocus amount detecting device.
Thus an accurate object distance can be detected.
* * * * *