Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Field of the_Invention:
The present invention xelates generally to an auto focus
system and is directed more particularly to an auto focus system
which is particularly suitable for use with a television camera
which includes, for example, a zoom lens.
Description of the Prior Art:
A prior art camera is described in the Paqel U.S. Patent
No. 3,442,193, in which a focusing state is detected and displayed
on a view finder. Also, known in the prior art is a system for
automatically controlling the ~ocusing state of the camera by
utilizing the above focusing state detecting sys~em.
BRIE~ DESCRXPTION OF THE DRAWINGS
Fig. 1 is a schematic diagram showing the construction of
a conventional auto focus system;
Figs. 2A to 2C are diagrams used to explain the conven-
tional auto focus system shown in ~ig. 1;
Fig. 3 is a schematic diagram showing one ~mbodiment of
the auto focus system according to the present invention; and
Figs. 4A and 4B are explanatory diagrams useful for show-
ing the effect which the auto focus system according to the present
invention can achieve.
In one such auto focus system, a conventional auto focus
system is employed as illustrated in Fig. 1. Shown in Fig. 1 is
an arrangement in which reference numeral 1 denotes a pick-up or
camera lens and 2 designates a focusing screen. The lens 1 iB
provided with a focus adjusting mechanism and the focus adjusting
mechanism is driven by a driving member or driver 3. There is
further provided a light source 4 and a light receiving member 5
used to measure a distance between an object and a camera body.
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9 light source 4 radiates, for example, an infrared radiation
beam toward the optical axis of the lens 1 and the light
receiving direction of the light receiving member 5 is changed
along a plane which includes an infxared radiation beam emitted
from the light source 4 and the ~ptical axis of the lens 1, so
that a light, which is the infrared radiation beam fr~m the
light source 4 strikes an object 6 and is reflected and detected
thereby. This detecting signal from the light receiving member S
is delivered to a si~nal processing circuit or processor 7 to
measure the distance,.
In other words, in case of measuring the distance, the
light sourcc 4 is illumin~ted by tl-e signal derived from the
processor 7 and at the same time, the light recPiving direction
of the liaht receiving member 5 is gradually changed or displaced
from the direction parallel to the optical axis of the lens 1 to
the inside as shown by an arrow P in Fig. 1. When the reflected
light beam from the object 6 is detected by the light receiving
member 5, the detected signal responsive to the angle of the
light receiving direction of the light receiving member 5 is
supplied to the processor 7 to measure the distance from the camera
body to the object 6.
A signal responsive to the measured distance is delivered
from the processor 7 to the driver 3 to adjust the focus or focal
point of the lens 1.
Further, as shown in Fig. 1, the pick-up lens 1 is also
provided with a 200m system 8. In this example of the prior art
auto focus system seen in the figure, the zoom system 8 consist~
of a concave lens 8a and a convex lens 8b and is used as a
telephoto lens by locating the concave lens 8a near the convex
lens 8b, and is used as a wide-angle lens by moving the concave
lens 8a away from the convex lens 8b. The focu5 adjustment of
this camera lens 1 i~ carried out in such a manner as to move a
convex lens la just befor~ and after. In this case, another
convex lens lb is formed as a fixed lens. As shown in Fig. 1,
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letter W represents a range of luminous flux receiv~d from the
~bject 6 in case o the wide angle lens mode and letter T
represents a like range of the telephoto lens mode, respectively.
In this auto focus system, owing to the fact that the
lens 1 and the optical system composing the light source 4 ~nd
and the light xeceiving member 5 for the distance measuring are
all independently constructbd, even if the optical field of the
lens 1, whieh i~ used for example, the zoom lens, i5 changed in
each case of the telephoto and wide-angle lenses, a range S of
irradiated luminous ~lux emitted from the light source 4 is not
altered.
To describe this more specifically with reference to
Figs. 2A to 2C, Fig. 2A describes a case, for example, where the
zoom lens is utilized as the standard lens. In this case, the
object 6, which will be displayed or projected on a view finder F
of the camera, is indicated thereon as shown in the figure. It
is assumed that the range S of the irradiated luminous flux at this
time will be represented by a broken line D. On the othPr hand,
Fig. 2B shows a case in which the zoom lens is used as the tele-
photo lens and therefore the object 6 is enlarged as illustrated
in the figure. At this time, although the range S of the
irradiated luminous flux stays within the fixed range relative
to the object 6, the distance measuring range is forced to be
enlarged to cover almost all area of the field as shown by one
dot chain line D' in accordance with the fact that the object
6 displayed within the finder F is also enlarged. Further, Fig.
~C describes a case in which the zoom lens is used as the wide
angle lens and the object 6 to be displayed within the finder
F is reduced as ilIustrated in the figure and the distance
measuring range (shown by two dots chain line D'~ in FigO 2C~
becomes small.
As described abov2, in case of the zoom lens, an apparent
di~tance measurang range relative t~ the frame of th~ view finder
F i~ fluctuated. But, in these cases, although the dis ance
measuring rnages D' and D" to the frame of the vi~w finder F are
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~ ased or reduced, such increase or reduction is not perceivableon the view finder F, so that it can not be known after all where
or whether the object 6 is precisely focused.
In other words, in such cases, user is apt to hanale the
camera system while to believe the distance measuring range as
being fixed ~shown by the broken line D). As a result, when the
zoom lens is used as, for example, the telephoto lens, there is a
fear that if another object exists between the distance measuring
ranges D (shown by the broken line) and D' Ishown by one dot chain
line) which is before or after that object 6, the focus adjustment
will be forced to be made before or after that object 6 even when
that object 6 is caught within the broken line D on the finder F
in Fig. 2B. This results in such a defect that when a picture of
a round-shaped object such as a human figure is taken, the focus
adjustment is liable to be per~ormed around the part of the
object to be picked up, so that the focus is not correctly made
coincident with the intended part of the object. When the zoom
lens is used as the wide-angle lens, even if the object 6 is
caught within the broken line D on the finder F as seen in Fig. 2C,
there is also a fear that the focus adjustment will not be per-
formed when the object 6 exists outside of two dots chain line D".
In this case, in case of the telephoto lens, since the
depth of the field is small, it is necessary to adjust the focus
correctly. On the other hand, in case of the wide-angle lens, it
is permissible that the focus may be adjusted roughly to a certain
extent because the depth of the field thereof bPcomes large. In
other words, in case of the known auto focus system as set forth
above, the precision on the distance measurement is lost parti-
cularly when the zoom lens is used as the telephoto lens which
normally requires high precision in focus adjustment.
OBJECTS AND SVMMARY C)F THE INVENTION ~
Therefore, it i~ an object of this invention to provide an
auto focus system which can remove the aforedescribed de~ects
inh~rent to the conventional auto focus system.
It is another object of this invention to provide an auto
focus system which is simple in construction and which can prevent
the occurrence of the a~ove men~ioned fluctuation of ~he distance
measuring range.
According to an aspect of the present invention, there is
provided an auto focus system comprising a pick-up lens ~ncluding a
zoom lens system, a distance measuring light source and a distance
measuring light receivin~ portion, the pick-up lens having a focus
adjusting mechanism, the distance measuring light source beina
illuminated, and a detecting device is provided for detecting the
angle of the reflected light beam emitted from th~ light source and
reflected by an object, the focus adjusting mechanism beinq driven
in accordance with the detected distance measurement output and
either of the distance measuring light source and the distance
measuring light receiving portisn being disposed behind the zoom
system within the pick-up lens.
The other objects, ~eatures and advantages of the present
invention will become apparent from the ~ollowing description taken
in conjunction with the accompanying drawings through which the
like references desi~nate the same elements and parts.
DESCRIPTION OF T~E PREFERRED EMBODIMENT
Now, one embodiment vf the auto focus system according to
the pre ent inv ntio~ will hereinafter be described with reference
to the attached drawings.
As shown in Fig. 3, a half mirror 9 having an angle 45~
relative to the optic~l axis of the lens system is provided between
these zoom system 8 and the convex lens of the lens system 1. The
light receiving mem~er 5 ~or measuring the distance is locat~d at
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the position where the optical axis of the lens 8ystem 1 is
~ ec~ed by the half mirror 9. The light ~ource 4 i5 provided at
the p~sition of the light receiving member 5 as was previously
illustrated in Fig. 1. ~he irradiation direction of the beam
irradiated from this light source 4 is adapted to change along a
plane which includes the optical axis of the lens 1.
In the auto focus system of the present invention thus
arranged, the distance measurement i~ carried out as follows. When
it is desired to perform the aistance measurement, the light
~ource 4 is illuminated by the signal derived from the processor 7
and the irradiation direction of the light beam therefrom is
changed from the direction parallel to the sptical axis of the lens
1 to the inside gradually, as indicated by the arrow P. When the
reflected light beam reflected by the object 6 is entered in~o the
convex lens la, then it is passed thr~ugh the zoom system 8 and
reflected by the half mirror 9 so as to be introduced into the light
receiving member 5, the detecting signal responsive to the angle
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of the irradiation clirection of the beam emitted from the light
source 4 is delivered -from the liyh-t receiviny member 5 to the
processor 7 by which the distance from the camera body to the
objec-t 6 is measured.
Therefore, in accordance wi-th this system, since the light
receiving member 5 is located behind the zoom system 8~ the ranqe
(distance measuring range) of the light received by the light
receiving member 5 becomes always fixed by following the field
enlarged or reduced by the zoom system 8 and the distance measur~
ing ranges in the telephoto and wide-angle lenses make the cons-tant
values against the frame of the view finder F, so that the object
6 can be ascertained ~ithout difficulty. In other words, as
shown in Fig. 3, in case of the telephoto lens, the distance
measurement is carried out in the range shown by one dot chain
line T, and in case o the wide-angle lens, the distance measure-
ment is performed in the range shown by two dots chain line W.
In case of the telephoto lens, the dis-tance measurement is carried
out with the accuracy higher than the wide-angle lens. Because,
in the wide-angle lens mode, the focal position of the reflected
light against all areas of the object 6 is largel~v moved within
the range shown by 1W in Fig. 3, thus giving rise to the scattering
of the focal position. On the contrary, in the telephoto lens
mode, the area of the re~lected light is quite narrow, so tha~ the
focal position is only moved within the range shown by LT in Fig.
3. Accordin~ly, the precision in the focus adjustment is improved
more in the telephoto lens mode as compared with the wide-angle
lens mode.
In this way, the distance is measured and the focus of the
lens 1 is adjusted. According to the embodiment of this invention,
since the distance measuring range on the view finder F is not
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changed in both cases of -the telep~o-to and wicle~an~le lenses,
there is no possibility that the user may misoperate the auto
focus sys-tem. In addition, in case of the -telephoto lens, the
more accurate distance measurement is carried out and -therefore
good focus adjustment can always be done.
Fur-ther, although in case of the prior ar-t auto focus
system as seen in Fig. 1, there is a fear that the error in
measuring the distance will occur especially when the short
distance measurement is done, since the beam from the light
source 4 is spaced apart from the optical axis of the lens 1,
according to the auto focus system of the present invention, the
light receiving member 5 is so arranged -that the ligh-t receiving
member 5 receives the light passed through the optical axis of
the lens system 1, so that there is no fear that the aforesaid
error in measuring the distance will be caused. ~his will be
described with reference -to Figs. 4A and 4B wllich respectively
illustrate the presence or absence of a so-called parallax in
measuring the distance in case of -the convent:Lonal auto focus
system and the system according to the presen-t invention. In
the figures, reference numeral ]0 designates a camera body. As
shown in Fig. 4~, due to the fact that the irradiation direction
of the infrared light emitted from the light source 4 is fixed in
the prior art, irradiated areas Sx, S~, Sz against objects X, Y
and Z by the light from the light source 4 are displaced in
response to the distance of the objects X, Y and Z Erom the camera
body 10. Accordingly, the value of the luminous flux to be
detected by the light receiving member 5 is changed by the distance
occupied by the camera body 10 and the objec-ts X, Y and Z, thereby
giving rise to the error in measuring the distance. Fig. 4B
illustrates the case of the present invention in ~hich the light
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source and the light receiving member are exchanged as compared
with those of Fig. 3. In case oE Fig~ ~B, the infrared light is
emitted from a light source 12 buil-t in the camera body 10 to
irradiate the respective objects X, Y and ~ by way of ~ mirror 13.
In accordance with this example, i-t is understood that the
irradiated areas Sx Sy and Sz are always made coincident with the
respective objects X, Y and Z irrespective of the distances
occupied by the camera body 10 and the objects X, Y and Z each and
therefore no parallax occurs.
In case of the conventional auto focus system as shown in
Fig. l, since there are provided the light source 4 and the light
receiving member 5 in addition to the lens 1, this greatly re-
stricts the well-known auto focus system in design. But,
according to the auto focus system of the present invention, since
only the light source 4 is prepared in addition to the lens 1, the
aforementioned restr.iction in design upon the system is largely
reduced.
In the auto focus system according to the present inven-
tion, the half mirror 9 is formed of a dichroic mirror which re-
flects the beam of the infrared rays to introduce it into the
light receiving member 5 and which also serves to introduce a
visible light into a target screen (not shown) of the pick-up
tube.
Therefore, according to this invention, it becomes
possible to measure the distance without a cut filter of the
infrared rays which is normally located in front of the pick-up
tube.
While in this embodiment there is disclosed the auto focus
system in which any one of the light source and the light receiving
member is relatively rotated to measure the distance of the o~ject
away from the camera body, the embodiment of the present invention
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is not limited to the aforesaid embodiment and such modi:Eication
may also be possible for example, that both of the light source and
light receiving member are no-t rotatably moved but fixed and
instead, there is simply provided two light receiving members in
parallel to each other whereby the rotation angles of the light
receiving members are made correspondent to the output ratio of
these two light receiving members to detect the focus.
In this case, in the afore described arrangement, it may
also be possible that the arrangement of the light source ~ and
the light receiving member 5 is exchanged as shown in Fig. 4B,
but instead, the light source 4 is located within the lens 1.
The above description is given on a single preferred em-
bodiment oE the invention, but it will be apparen-t that many
modifications and variations could be effected by one skilled in
the art without departing from the spirit or scope o~ the novel
concepts of the invent.ion, so that the scope of the inven-tion
should be de-termined by the appended claims only.
