JP4284223B2 - Dome camera and dome cover - Google Patents

Description

  The present invention relates to a dome type camera in which a lens is accommodated in a dome cover.

  As a conventional dome type camera, for example, a surveillance camera is known, and a general surveillance camera includes a lens housed in a dome cover and a rotation mechanism that rotates the lens in a tilt direction and a pan direction. Yes.

In a dome type camera, a dome cover and a lens may be arranged such that the lens optical axis is offset from the center of the dome to the dome top side (see, for example, Patent Document 1). Such an arrangement enables photographing in a direction parallel to the mounting plane without causing vignetting. Here, vignetting means that the image becomes partially dark because the camera housing or the like enters a part of the shooting range.
JP 2000-244783 A (2nd page, FIG. 1)

  However, in the conventional dome type camera, as described below, when the lens optical axis is offset with respect to the center of the dome, an aberration caused by the dome cover occurs, and this aberration deteriorates the image quality.

  The problem of the aberration will be described with reference to FIG. In FIG. 4, the lens 100 is accommodated in the dome cover 102 and is arranged so as to face the horizontal direction. The optical axis 104 of the lens 100 is offset in the dome zenith direction with respect to the center 106 of the dome cover 102. An upper ray 108 and a lower ray 110 in the figure are rays that are parallel to the optical axis 104 and enter the vicinity of the upper end and the lower end of the lens 100.

  As shown in FIG. 4, since the lens 100 is offset, the optical path length a of the upper light beam 108 and the optical path length b of the lower light beam 110 at the cover portion are different, and the latter is longer. Here, the optical path length in the cover part (cover passing part) is the length of the part in the cover in the optical path, and corresponds to the thickness of the cover in the direction along the optical path. An aberration is caused by the difference between the optical path lengths a and b.

  More specifically, when the angle α between the upper light beam 108 and the cover surface is compared with the angle β between the lower light beam 110 and the cover surface, the angle α is larger than the angle β. That is, the lower light beam 110 is incident on the dome cover 102 obliquely as compared with the upper light beam 108. Due to such a difference in angle, the optical path length b of the lower light beam 110 at the cover portion is longer than the optical path length a of the upper light beam 108. This optical path difference causes aberrations.

  In this way, when the dome cover 102 is offset, the dome cover 102 functions as an asymmetric optical system member that constitutes a part of the optical system and causes aberration. The larger the tilt angle, the larger the aberration, and the image quality deteriorates. The sensation of the subject may even appear double.

  The above-mentioned problems are not so noticeable with surveillance cameras specialized in wide-angle shooting, which has been common in the past. However, with the widespread use of surveillance cameras, surveillance cameras have a zoom function and take high-magnification images. When the magnification is increased, the above-mentioned aberration problem becomes remarkable.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a dome capable of obtaining a good image even when the lens optical axis is offset in a surveillance camera capable of high magnification zoom photography. To provide a type camera.

The dome type camera of the present invention has a lens and a dome arranged so that the outer surface or the inner surface is spherical and the optical axis of the lens is offset to the dome zenith side from the center of the outer surface or inner surface having a spherical shape. The dome cover is configured such that the cover wall thickness increases as the tilt angle from the dome top direction increases. Here, the cover thickness may continuously increase over the entire range of the dome cover. Further, the cover thickness may be increased stepwise. The cover wall thickness may be increased according to the tilt angle in a part of the area, not in the entire range of the dome. For example, the cover thickness may be constant when the tilt angle is less than a predetermined size, and the cover thickness may be increased according to the tilt angle when the tilt angle is greater than the predetermined size.

  With this configuration, when photographing a direction with a large tilt angle such as a horizontal direction, the optical path difference in the cover portion of the light beam passing through both ends of the lens is reduced, thereby reducing the aberration and improving the image quality.

  In the dome type camera of the present invention, the outer surface and the inner surface of the dome cover are spherical, and the center of the inner surface is offset to the dome zenith side from the center of the outer surface. Thereby, the dome cover of the present invention in which the cover wall thickness changes according to the tilt angle can be easily manufactured.

In another aspect of the present invention , the outer surface or the inner surface is spherical, and the lens is arranged such that the optical axis of the lens is offset from the center of the outer surface or inner surface that is spherical to the dome zenith side. The cover is configured such that the cover thickness increases as the tilt angle from the dome zenith direction increases. In the present invention, the outer surface and the inner surface are spherical, and the center of the inner surface is offset to the dome zenith side with respect to the center of the outer surface. With such a configuration, the advantages of the present invention described above can be obtained.

  According to the present invention, there is provided a dome-type camera having an effect of improving image quality when photographing a direction with a large tilt angle such as a horizontal direction by changing the thickness of the dome cover according to the tilt angle. Is something that can be done.

  Hereinafter, a dome type camera according to an embodiment of the present invention will be described with reference to the drawings. In the present embodiment, the dome type camera is a surveillance camera.

  FIG. 1 is a diagram modeling a main part of the dome type camera according to the first embodiment of the present invention, and FIG. 2 shows an example of the entire configuration of the dome type camera.

  As shown in FIG. 2, the dome camera 10 has a base portion 12, and a lens 14 and a dome cover 16 are attached to the base portion 12. The base portion 12 is attached to the attachment object by the attachment portion 18. The attachment object is, for example, a ceiling.

  The base portion 12 is provided with a pan / tilt mechanism 20, and the pan / tilt mechanism 20 is provided with a lens 14, whereby the lens 14 is rotatable with respect to the base portion 12 in the pan direction and the tilt direction. The pan / tilt mechanism 20 includes a motor and may be moved by remote operation. The pan / tilt mechanism 20 may be a manual type. The lens 14 has a configuration in which a plurality of lenses are assembled to a lens barrel. An imaging device such as a CCD is incorporated behind the lens barrel, thereby constituting a camera.

  The dome cover 16 is attached to the base portion 12 in a state where the lens 14 is accommodated. The dome cover 16 is made of polycarbonate or acrylic, and is transparent. The dome cover 16 is generally a hemisphere. The optical axis of the lens 14 is offset toward the dome top side with respect to the center of the dome cover 16 (that is, the center of the hemisphere). The offset amount A in FIG. 2 is the magnitude of the offset when the optical axis is horizontal. Specifically, the offset amount is the length of a perpendicular line from the center of the dome to the optical axis, and changes according to the direction of the lens 14. With this offset, even when the lens 14 faces in the horizontal direction, the lens 14 can photograph the front without being obstructed by the base portion 12.

  Here, the angle formed by the dome zenith direction and the optical axis of the lens is called a tilt angle. The tilt angle when the lens 14 (lens optical axis) faces the dome zenith is zero. The tilt angle when the lens 14 (lens optical axis) is oriented in the dome horizontal direction is 90 degrees. In the present embodiment, since the dome-type camera 10 is installed downward on the ceiling, the tilt angle is 0 degree when the lens 14 faces directly below.

  Referring now to FIG. 1, both the outer and inner surfaces of the dome cover 16 are hemispheres. However, as a feature of the present embodiment, the center O2 of the inner hemisphere is offset toward the dome zenith side with respect to the center O1 of the outer hemisphere. Thereby, the dome thickness (thickness in a direction perpendicular to the dome surface) at the dome zenith T is thinner than the thickness in the dome horizontal direction. As the tilt angle from the dome zenith T increases, the dome thickness increases. Further, as already described, the lens optical axis 30 is offset toward the dome zenith T side with respect to the dome center O1.

  In FIG. 1, the lens 14 is oriented in the horizontal direction (tilt angle is 90 degrees). An upper light beam 32 and a lower light beam 34 in the figure are light rays that are parallel to the optical axis 30 and enter the vicinity of the upper end and the lower end of the lens 14. In the present embodiment, since the cover thickness changes according to the tilt angle, the optical path length a of the upper light beam 32 at the cover portion is substantially equal to the optical path length b of the lower light beam 34. The optical path length in the cover part (cover passing part) is the length of the part in the cover in the optical path, and corresponds to the thickness of the cover in the direction along the optical path.

  This will be described in more detail. In FIG. 1, the angle α formed by the upper light beam 32 with the cover surface is about 90 degrees. On the other hand, the angle β formed by the lower light beam 34 with the cover surface is smaller than 90 degrees. It can also be said that the lower light beam 34 enters the dome cover 16 more obliquely than the upper light beam 32. Here, if the dome thickness is uniform as in the prior art, the optical path length a of the upper light beam 32 at the cover portion is shorter than the optical path length b of the lower light beam 34 due to the above-described angle difference.

  However, in the present embodiment, the cover thickness increases in accordance with the tilt angle. This change in thickness cancels out the change in optical path length due to the above-described angle difference. As a result, the optical path lengths a and b at the cover portions of the upper light beam 32 and the lower light beam 34 are substantially equal. Further, since the difference between the optical path lengths a and b of the upper light beam 32 and the lower light beam 34 is reduced, the aberration due to the optical path difference is reduced.

  The operation of the dome type camera 10 described above will be described. In the dome type camera 10, the lens 14 is rotated in the tilt direction by the pan / tilt mechanism 20.

  First, the case where the lens 14 faces the dome zenith direction (tilt angle is 0 degree) will be described. Although this state is not shown, since the dome cover 16 is rotationally symmetric, when the lens 14 faces the dome zenith direction, there is no difference in optical path between the cover portions at both ends of the lens 16. Therefore, no aberration occurs in the cover portion, and a high-quality image can be obtained.

  Next, in the state of FIG. 1, the lens 14 is oriented in the horizontal direction (tilt angle is 90 degrees). Also at this time, as described above, in the present embodiment, the optical path difference between both ends of the lens in the cover portion is reduced, so that the aberration due to the optical path difference is small. As a result, a good quality image can be obtained even when shooting in the horizontal direction.

  Thus, the optical path difference at the cover portion of the light beam passing through both ends of the lens 16 is small both when the lens 14 faces the dome zenith direction and when it faces the dome horizontal direction. Further, when the lens 14 is oriented in any direction between the dome zenith direction and the dome horizontal direction, similarly, the optical path difference is small, the aberration is small, and a good image can be obtained.

  FIG. 3 is a simulation result of the optical path length (the dome penetrating portion) of the above-described upper ray and lower ray, and shows a comparison result between the present invention and the conventional configuration.

  In the conventional example, when the tilt angle is 90 degrees, the offset amount of the lens optical axis from the dome center is 15 mm, and the diameter of the lens 12 is 48 mm. The dome outer diameter is 150 mm and the dome inner diameter is 145 mm. The centers inside and outside the dome are coincident, so the dome thickness is 2.5 mm and uniform.

  On the other hand, in the example of the present invention, the offset amount (eccentric amount) of the center of the dome inner diameter with respect to the center of the dome outer diameter is 0.4 mm. Therefore, the thickness in the dome top direction is 2.1 mm, and the thickness in the dome horizontal direction is 2.5 mm, and the thickness increases during this time. Others are the same as the conventional example. The lens optical axis offset of 15 mm is the distance from the center of the dome outer diameter.

  As shown in FIG. 3, in the conventional example, when the tilt angle is 0 degree (the zenith direction), the optical path difference between the upper ray and the lower ray of the cover portion is almost zero. However, as the tilt angle increases to 45 degrees and 90 degrees, the optical path difference between the upper light beam and the lower light beam increases. In accordance with this optical path difference, aberration increases and image quality deteriorates. On the other hand, since the optical path difference is reduced in the example of the present invention as compared with the conventional example, the aberration is reduced, and thus the image quality is improved compared to the conventional example.

  As described above, according to the dome type camera 10 of the embodiment of the present invention, the cover thickness of the dome cover 16 increases in accordance with the tilt angle, so that a direction with a large tilt angle such as a horizontal direction is photographed. In this case, the optical path difference in the cover portion of the light beam passing through both ends of the lens 12 is reduced, thereby reducing the aberration and improving the image quality.

  Considering a surveillance camera, which is a typical example of a dome type camera, in a conventional surveillance camera specialized in wide-angle shooting, image quality degradation according to the tilt angle was not so significant. However, with the widespread use of surveillance cameras, surveillance cameras have a zoom function and perform high-magnification photography. In such a high-magnification shooting, the aberration of the conventional configuration greatly deteriorates the image quality, and it is possible that the image looks double in terms of feeling. Under such circumstances, according to the present embodiment, the image quality can be greatly improved.

  In the dome type camera 10 according to the embodiment, the outer surface and the inner surface of the dome cover 16 are spherical, and the center of the inner surface is offset to the dome zenith side with respect to the center of the outer surface. By adopting such a configuration, it is possible to easily manufacture a dome cover whose cover thickness suitably changes according to the tilt angle.

  In the present embodiment, the thickness of the dome cover 16 continuously increased over the entire range from the zenith direction to the horizontal direction. However, the present invention is not limited to such a configuration. For example, the cover wall thickness may increase stepwise. Further, the cover thickness may be increased not in the entire range of the dome but in a part of the region. For example, the cover wall thickness may be constant in a predetermined tilt angle range including the dome zenith, and the cover wall thickness may increase in accordance with the tilt angle in a horizontal region exceeding the predetermined range.

  Further, in the above embodiment, the inner surface of the cover is a spherical surface, which makes it easy to manufacture the dome cover 16. However, the present invention is not limited to the above configuration. One or both of the outer surface and the inner surface may be a rotationally symmetric curved surface whose curvature gradually changes. Also in this case, the advantage of the present invention can be obtained if the cover thickness increases in accordance with the tilt angle.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and it goes without saying that those skilled in the art can modify the above-described embodiments within the scope of the present invention.

  As described above, the dome camera according to the present invention has an effect of improving the image quality, and is useful as a surveillance camera or the like.

The figure which shows the dome shape camera in embodiment of this invention The figure which shows the dome shape camera in embodiment of this invention The figure which shows the comparison of the dome shape camera in embodiment of this invention, and a prior art example Diagram showing a conventional dome camera

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Dome type camera 12 Base part 14 Lens 16 Dome cover 20 Pan tilt mechanism 30 Optical axis 32 Upper ray 34 Lower ray

Claims (4)

A lens,
A dome cover arranged such that the outer surface or the inner surface is spherical and the optical axis of the lens is offset from the center of the spherical outer surface or inner surface to the dome zenith side;
The dome cover is configured such that the cover wall thickness increases as the tilt angle from the dome zenith direction increases.   The dome type camera according to claim 1, wherein the outer surface and the inner surface of the dome cover are spherical, and the center of the inner surface is offset to the dome zenith side with respect to the center of the outer surface. A dome cover in which the outer surface or the inner surface is spherical and the lens is arranged so that the optical axis of the lens is offset from the center of the outer surface or inner surface that is spherical to the dome zenith side, from the dome zenith direction A dome cover characterized in that the cover wall thickness increases as the tilt angle increases.   The dome cover according to claim 3, wherein the outer surface and the inner surface are spherical, and the center of the inner surface is offset toward the dome zenith side with respect to the center of the outer surface.

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