JP2864178B2 - Lens barrel for surveillance camera - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens barrel for a surveillance camera , and more particularly to a lens barrel for reducing an image jump phenomenon caused by a movement of a principal point of a focus lens group.

[0002]

2. Description of the Related Art A helicoid structure is widely used in a lens barrel as a focusing mechanism for moving a focusing lens in an optical axis direction. In this helicoid structure, basically, a male helicoid is provided on one of two annular members (for example, a fixed ring) that rotate relatively,
The other (for example, a focusing ring on which a focus lens group is mounted) is provided with a female helicoid screwed to the male helicoid. When the focusing ring is rotated with respect to the fixed ring, the focusing ring (focus lens group) moves in the axial direction according to the lead angle of the helicoid, and focusing is performed.

Instead of the helicoid mechanism, a focusing mechanism is also known in which a focusing ring is provided with a lead groove having a specific lead angle, and a fixed ring is provided with a roller which fits into the lead groove. These are all the same in that two relatively rotating annular members are displaced in the axial direction with the relative rotation, and the focus lens group is mounted on one of the annular members.

In this focusing mechanism, there is always a clearance between the two annular members in the fitted state. The focus lens group can move a small distance in a direction parallel to the optical axis according to the clearance, or the optical axis may be tilted. In particular, in a surveillance camera, when focusing is performed by a motor drive, if a rotational driving force is applied to one of the annular members via a gear, the focus lens group falls down, and the principal point position shifts with respect to the optical axis due to this. (Hereinafter referred to as principal point shift) is inevitable.

[0005] The movement of the principal point of the focus lens group is not a problem in a still camera as long as the movement is small.
However, in a surveillance camera that forms an image from a lens on an image pickup device such as a CCD and observes the image on a monitor TV, if the principal point moves due to a change in the focusing direction or the like during observation. This causes a so-called image skipping phenomenon, which is not only very difficult to see, but also impairs reliability.

[0006] In particular, a recent surveillance camera has an image sensor size of 1 inch (about 15.9 mm diagonal) from the initial size of 1 inch.
/ 3 inch (11.0mm), 1/2 inch (8.0mm),
The size is reduced to 1/3 inch (6.0 mm), and since this is magnified and observed on a monitor TV, slight image skipping is observed as large image movement. For example, 20 inches (500m
The image movement distance of 1 mm on the monitor TV in m) corresponds to an image movement of 32 μm on a 1-inch image sensor, 22 μm in 2/3, 16 μm in 1/2 and 12 μm in 1/3. When the image movement on these image sensors is converted into the movement distance of the principal point of the focus lens group from the optical axis, for example, the following table is obtained. That is, the main point movement amounts of the focus lens group from being transmitted to the image plane at a ratio ,, f / f ₁ of the focal length f ₁ of the composite focal length f and the focusing lens group of the entire lens system, for example, present Assuming that the combined focal length f = 56.3 mm on the long focal length side and the focal length f ₁ of the focus lens group f ₁ = 41.5 mm in the example optical system, f / f ₁ = 1.3566, and the principal point movement amount of the focus lens group is With a coefficient of 1.3566,
It is a value obtained by dividing the amount of image movement on the image sensor.

[0007]

[0008] This means that, under the above assumption, 1 /
In order to keep the image movement on a 20-inch monitor TV to 1 mm or less using a 3 ″ camera, the clearance A between the two fitting members must be 9 μm or less. Is the current mass production technology,
Inexpensive product production is a practically difficult figure.

On the other hand, in the current mass production technology, it is possible to obtain a clearance of about 30 to 60 μm in the case of helicoid fitting. By intervening, apparently image skipping can be prevented. That is, when the high-viscosity lubricating oil is interposed, the movement of the two fitting members becomes slow, and the image jump becomes inconspicuous. But,
When a high-viscosity lubricating oil is interposed, there is an unavoidable problem that the usable temperature range is narrowed. The solution of interposing a high-viscosity lubricating oil cannot be used in severe use conditions.

Further, the amount of image skipping due to the movement of the principal point of the focus lens unit is determined by setting the focal length of the focus lens unit to f ₁ ,
When the focal length of the entire lens system is is f, it is transmitted to the image plane at a ratio of f / f _1. Surveillance cameras generally consist of zoom lenses, which require higher zoom magnifications.
On the long focal length side, f / f ₁ becomes 1.3 to 1.5. Therefore, in a high-magnification zoom lens, the above-mentioned problems are more closely observed on the long focal length side.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the problem of image skipping caused by the movement of the principal point of a focus lens group of a surveillance camera lens barrel .

[0012]

SUMMARY OF THE INVENTION According to the present invention, it is possible to prevent the movement of the principal point of the focus lens group by uniformly increasing the fitting accuracy of two members fitted to each other from the viewpoint of processing technology and processing cost. In consideration of the lack of accuracy, a lens barrel having a structure in which the fitting clearance between the two annular members, which cannot be avoided in processing, has little effect on image skipping is obtained.

According to the present invention, two relatively rotating annular members are provided.
A lens barrel that is fitted in such a way that it is displaced in the axial direction with relative rotation, and a focus lens group is mounted on one of the members
Wherein an image formed by the lens barrel is formed on an image sensor.
Into a lens barrel for a surveillance camera to observe on a monitor TV
Between the fitting clearance of the two annular members
The principal point position of the lens group or a position closer to the image plane side than the principal point position
By location, between the fitting clearance of the annular second member,
It is characterized in that a tilting fulcrum is provided near the principal point of the focus lens group.

As described above, if the tilt fulcrum is provided near or behind the principal point, the amount by which the principal point of the focus lens group can move in the direction orthogonal to the optical axis is limited. Therefore, the amount of image jump can be reduced. Of course, the optical axis of the focus lens group may be tilted around the tilt fulcrum, but the tilt of the focus lens group without moving the principal point does not cause image jump.

Strictly speaking, it is preferable that the falling fulcrum coincides with the position of the principal point (second principal point) of the focus lens group. However, if it is provided behind the principal point , sufficient practical effect can be obtained. Can be obtained.

Specifically, the falling fulcrum can be constituted, for example, by a plurality of fulcrum screws in the radial direction screwed from one of the two annular members toward the other. Alternatively, it may be constituted by a plurality of elastically deformable elastic members inserted between two annular members.

The fitting clearance a in the falling fulcrum screw portion may be set by linking to the allowable range of the amount of image movement on the monitor TV, but 0 <a <0.01.
(Mm) . The setting for this amount is
After once applying the falling fulcrum screw to the mating annular member,
The adjustment operation can be performed relatively easily by slightly returning the adjustment operation.

The falling fulcrum can also be constituted by an elastic fulcrum member. In the case of this elastic fulcrum member, a counterbore depth (hole) for installing the elastic fulcrum member is set so that an elastic force capable of controlling the amount of tilt can be obtained with respect to the external pressure of the focusing operation, and It is preferable that the above-mentioned 0 <a <0.01 (mm) is obtained without performing the adjustment operation as in the case.

[0019]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
FIG. 6 shows the overall configuration of a surveillance camera lens to which the present invention is applied. In order from the object side, a focus lens unit L1, a variable power lens unit L2, and a compensator lens unit L3 are shown.
And a master lens group L4. Each lens group
L1 to L4 are supported by the respective lens frames 11, 12, 13 and 14.

The lens frame 11 is fixed to a focusing ring 16 located on the outer periphery of a fixed cylinder 15. A male helicoid 17 and a female helicoid 18 screwed to each other are formed on the fixed cylinder 15 and the focusing ring 16. ing. The lens frames 12 and 13 are linearly guided by the fixed barrel 15 and move in the optical axis direction by rotation of a cam ring 19 rotatably fitted on the inner circumference of the fixed barrel 15. The master lens unit L4 is fixed to the fixed barrel 15. An annular gear 16a is fixed to the outer periphery of the focusing ring 16, and a pinion (not shown) meshes with the annular gear 16a. This pinion is driven by a motor.

The falling fulcrum, which is a feature of the present invention, is provided between the fixed cylinder 15 and the focusing ring 16.
1 and 2 show a first embodiment. Three falling fulcrum screws 20 are screwed around the outer periphery of the focusing ring 16 at 120 ° intervals. The clearance a between the tip and the fixed cylinder 15 of the falling fulcrum screw 20 can be adjusted by adjusting the screwing amount.

The falling fulcrum screw 20 is located behind (the image plane side) the principal point (second principal point H ₂ ) of the focus lens unit L1.
It is provided to be placed . The clearance a between the tip of the falling fulcrum screw 20 and the fixed barrel 15 is set such that A> a, where A is the total clearance between the fixed barrel 15 and the focusing ring 16. And a
Is 0 < for a 1/3 "lens, as described above.
a <0.01 (mm) is preferable.

As described above, when the falling fulcrum screw 20 having a clearance smaller than the clearance between the fixed barrel 15 and the focusing ring 16 is provided near the principal point of the focus lens unit L1, it is separated from the optical axis of the principal point. Directional displacement is limited. For this reason, the phenomenon of image skipping hardly occurs,
It is small even if it occurs.

FIGS. 3 and 4 show a second embodiment of the present invention. This embodiment uses an elastic fulcrum member 21 in which the clearance a is preset, instead of the falling fulcrum screw 20 of the first embodiment in which the clearance a can be adjusted. The elastic fulcrum member 21 has a hemispherical shape, a large-diameter portion is fitted into a counterbore recess 22 formed in the fixed cylinder 15, and the spherical surface at the tip thereof is in elastic contact with the inner surface of the focusing ring 16. The strength of the elastic force is determined by the elastic fulcrum member 2.
If 1 has the same shape, it can be set by setting the depth of the counterbore recess 22.

In setting the elastic force of the elastic fulcrum member 21, taking into consideration that a pinion pressure from a motor indicated by an arrow is applied to the focusing ring 16 via an annular gear 16a, the falling of the focusing ring 16 is determined by the focus lens. The elastic fulcrum member 21 is determined to be generated near the main point of the group. Accordingly, when the elastic fulcrum member 21 is used, the above-mentioned operation can be performed without performing the adjusting operation.
A condition corresponding to 0 <a <0.01 (mm) can be given. On the other hand, the elastic fulcrum member 21 supports the large-diameter portion in a counterbore recess provided on the focusing ring 16 side,
The tip may be configured to contact the outer surface of the fixed cylinder 15.

The position of the elastic fulcrum member 21 in the direction of the optical axis should coincide with the principal point of the focus lens unit L1.
Doo is desirable, in this embodiment, focus lens group L
A from principal point of the 1 backward (image plane side) are provided to match the surface position after full Okasurenzu group L1.

Next, the effects of the present invention will be described with reference to specific calculation examples. FIG. 5 shows a lens barrel having neither the above-mentioned falling fulcrum screw 20 nor the elastic fulcrum member 21 for comparison. FIGS. 1, 3 and 5 show specific examples of numerical values used as the basis for this calculation.

In the first embodiment, the position of the falling fulcrum screw 20 is about 2 mm behind the principal point of the focus lens unit L1.
In the second embodiment, the elastic fulcrum member 21
Is the position of the rear end face of the thickness of the focus lens unit L1, which is about 5 mm behind the principal point position. In the lens barrels of the first embodiment, the second embodiment, and the comparative example, the clearance A between the fixed barrel 15 and the focusing ring 16 is 0.
The same conditions as 05 mm (for example, the outer diameter of the fixed cylinder 15; 42.
16 mmφ, inner diameter of focusing ring 16; 42.21 mmφ, or the amount of loose play of helicoid screw is A = 0.05 mm). It is assumed that the maximum tilt of the focusing ring 16 occurs at a position 17.5 mm behind the principal point H2.

In the embodiment shown in FIGS. 1 and 2, the focusing ring 16 is tilted with the position of the tilt fulcrum screw 20 as a fulcrum. In the optical system of the embodiment, the principal point of the focus lens unit L1 is Since the distance from the falling fulcrum screw 20 is 2 mm ahead, the displacement x of the principal point with respect to the optical axis is 0.007 mm.
(7 μm) (x = 0.05 × 2 / 15.5).

In the embodiment shown in FIGS. 3 and 4, the focusing ring 16 falls down with the elastic fulcrum member 21 serving as a fulcrum.
Since the fulcrum position is about 5 mm rearward from the principal point of the focus lens unit L1, the shift amount x of the principal point with respect to the optical axis is 0.
02 mm (20 μm) (x = 0.05 × 5 / 12.5).

In the comparative example (conventional example) shown in FIG. 5, when the focusing ring 16 moves parallel to the optical axis, the displacement x of the principal point of the focus lens unit L1 with respect to the optical axis is 0.05 mm.
Becomes The displacement x due to the fall is 0.05 mm (50 μm). That is, in the conventional example, the clearance A is equal to the principal point movement amount of the focus lens unit L1.

In the above specific example (combined focal length f = 56.3 mm, focal length f ₁ of focus lens unit L1 = 41.5 mm), f /
f ₁ = 1.3566. Accordingly, in order to convert the shift amount of the principal point with respect to the optical axis in each of the examples and the comparative examples into the shift amount of the image plane, the shift amount x × 1.3566 is obtained.

[0033]

Further, this image is displayed on a monitor T of 20 inches.
When viewed from V, the image sensor for １ ／ ″ and 1 /
The magnification of the 2 "image sensor is 500 mm / 6 mm = 83.3 times in the case of the 1/3" image sensor; 500 mm / 8 mm = 62.5 times in the case of the 1/2 "image sensor.

The value obtained by multiplying the above-mentioned image plane movement amount by this magnification is the amount of image jump on the monitor TV.
The following table shows.

According to this calculation example, in the first embodiment of the present invention, since the falling fulcrum screw 20 is set at a position relatively behind the principal point position and relatively close to the principal point position, the monitor image is displayed.
The movement ratio to the surface is (0.63 / 500) × 100 = 0.13%,
(0.83 / 500) × 100 = 0.17%. Further, in the second embodiment in which the fulcrum member is set near the end face within the thickness and behind the principal point position of the focus lens unit L1, the movement amount ratios to the monitor screen are similarly set to (1.69). / 500) × 100 =
0.34%, (2.25 / 500) × 100 = 0.45%, which is acceptable as the amount of image jump on the monitor screen. On the other hand, in the comparative example (conventional example), (4.25 / 500) × 100 = 0.85
%, (5.66 / 500) × 100 = 1.13%, the moving amount ratio on the monitor screen is about 1%, and the image jump is conspicuous. As described above, according to the present invention, even if the clearance amount under the same condition is set between the two annular members, the accuracy of the image jump can be improved several times.

In the above embodiment, the fixed cylinder 15 and the focusing ring 16 are helicoid-coupled. However, the present invention can be applied to a focusing mechanism using lead grooves and rollers instead of the helicoid. it can.

[0038]

As described above, according to the present invention, two annular members which are relatively rotated are fitted in a relation of being displaced in the axial direction with the relative rotation, and the focus lens group is mounted on one of the members. In the lens barrel, the principal point movement of the focus lens group can be suppressed to a minimum, and the image jump phenomenon caused by the principal point movement can be suppressed. Therefore, especially the lens barrel
This is suitable as a surveillance television lens that forms an image on an image sensor and continuously observes the image on a monitor TV .

[Brief description of the drawings]

FIG. 1 is an upper half sectional view showing an embodiment of a lens barrel according to the present invention.

FIG. 2 is a sectional view taken along line BB of FIG.

FIG. 3 is an upper half sectional view showing another embodiment of the lens barrel of the present invention.

FIG. 4 is a sectional view taken along line CC of FIG. 3;

FIG. 5 shows a conventional lens barrel shown as a comparative example,
FIG. 4 is a sectional view corresponding to FIG. 3.

FIG. 6 is a side view showing an example of the entire configuration of a surveillance camera lens to which the present invention is applied;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Lens frame 15 Fixed ring (annular member) 16 Focusing ring (annular member) 20 Falling fulcrum screw (falling fulcrum) 21 Elastic fulcrum member (falling fulcrum)

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 7/04

Claims (4)

(57) [Claims] 1. A lens barrel having two annular members that rotate relative to each other so as to be displaced in the axial direction with relative rotation, and a focus lens group is mounted on one of the members.
The image formed by the lens barrel is formed on the
Surveillance camera lens barrel observed on Nita TV
Te, during the fitting clearance of the annular second member, position on the image plane side principal point position or the principal point position of the focus lens group
By location, monitoring turtle, characterized in that a falling fulcrum
Lens barrel for LA . 2. The lens barrel according to claim 1, wherein the fitting clearance a of the two annular members at the falling fulcrum is:
A lens barrel for a surveillance camera in which 0 <a <0.01 (mm) . 3. The surveillance camera according to claim 1, wherein the tilting fulcrum is constituted by a plurality of radial fulcrum screws screwed from one of the two annular members toward the other. use the lens barrel. 4. The lens barrel according to claim 1, wherein the tilting fulcrum is constituted by a plurality of elastically deformable elastic fulcrum members inserted between the two annular members.
Lens barrel for surveillance camera .