Patent Application
20100321494
This disclosure relates generally to video capture systems and more particularly to compact video capture systems with folded optical assemblies.
Video capture systems, such as closed circuit television (CCTV) dome cameras, are popular in the security market because they provide a record of activities occurring at a recorded location and because of their deterrent effect on potential wrongdoers. As these video capture systems have evolved from rudimentary analog video cameras with grainy recordings to more advanced digital systems, image quality and relative size of the video imaging equipment has become increasingly important. In many instances, the vertical dimension (overall thickness) of these systems is becoming more important with a desire to make them as thin as possible. A relatively thin vertical dimension allows them to be inconspicuously placed so as not to detract from the décor of the area that requires video surveillance.
Video capture systems generally use single linear optical path systems, which include a lens and image sensor, that are pointed toward a specified direction of view by rotation about a pivot point within a vertical plane. These systems can be angled from 0 degrees to 90 degrees and then rotated about a pivot axis normal to the plane of the mounting plane to allow video capture over an entire hemisphere or, with additional hardware, an entire sphere. In some cases a folded optical path has also been used. Folded optical paths also point toward an area of interest by rotation about a pivot axis normal to the plane defined by the longitudinal axes of the folded optical path.
To maintain a thin form factor, however, the longitudinal length of the optical path must be relatively short in length. This length limitation negatively affects the performance of the video capture system by reducing the length of the optical path available for the lens and by creating a size limitation on the image sensor. That is, the lens must be very compact in order to accommodate the optical path, which can limit the lens resolution, zoom capability, and may require a restricted F number. For high resolution image sensors of small size, the pixels are very small, decreasing the low light functionality of the system and increasing the potential for electronic noise in the image.
As discussed above, one issue with conventional video capture systems is that a reduction in size to the overall thickness of the image capturing hardware limits the longitudinal length of the optical path, which results in a reduction in the lens resolution and zoom capability while further requiring a restricted F number.
In a typical security camera setup, the video capture system 100 will be mounted on a level ceiling with a mounting plane 138 parallel to the ceiling. The direction of view 140 of the optical assembly 112 can be changed by rotating the optical assembly about a first rotational axis 142 to change the vertical direction of view and about a second rotational axis 144 to change the horizontal direction of view.
As opposed to this conventional system that requires limited lens performance as a tradeoff for a relatively small size, embodiments of the present invention provide a video capture system with far superior lens performance while maintaining or even reducing the compact size of the system. Some embodiments of the present concept obtain these advantageous aspects by providing a folded lens and optical assembly for use in a compact video system. These compact video systems may be implemented in a CCTV dome camera or digital security camera dome, although, the scope of this invention is not limited to these two camera systems. It is understood that embodiments of the invention may have utility in military, video conferencing, projection, and many other devices requiring an imaging lens with a variable or settable field of view.
In one embodiment of the invention, a folded lens is used in a video capture system. The lens, which is part of an optical assembly that includes the image sensor, has an entrance to capture light from an object and direct the light along a direction. This direction is usually parallel to the optical axis of the initial part of the lens. At some point within the optical system, the light intersects an optical fold element such as a mirror or prism and is redirected along a second direction. This second direction is usually approximately 90 degrees from the initial direction but could be configured at any other angle change. In an embodiment with only one fold element, this second direction is parallel to the optical axis of the final part of the lens and is generally perpendicular to the plane of the image sensor. After travelling along this new direction, the image is captured at an image sensor.
The optical fold in the system allows many advantages over video systems without this feature. The folded lens allows the video capture system to be compact without limiting the performance of the lens. This allows the dome of the video capture system to remain relatively thin and compact with a protective dome having a diameter on the order of, for example, 1 inch to 2 inches without limiting the lens length. The folded lens in this compact dome may still have longitudinal length of, for example, 40 mm to 120 mm or more.
The relatively long length of the lens allows the use of many different optical lens elements within the optical assembly. Each of these optical elements performs a small change to the direction of the light transmitting through the surfaces of the element. In total, the elements create a focused image of the object at the image sensor. Keeping the directional change of the light at each individual element small and the number of elements large allows a greater degree of control of the light at different field points in the pupil and image. This greater control allows the lens to be designed without unwanted aberrations such as coma, astigmatism, and chromatic aberration, all of which increase the blur spot size at the image sensor. This smaller blur spot achievable with the larger number of lens elements means that the lens has a high image resolution and can focus light from points of the object onto a small spot at the image sensor. This allows the image sensor to have very small pixels and thus a large number of pixels in a small area. The large number of optical elements required to minimize the optical aberrations requires a certain physical distance between the lens entrance and image sensor. By folding the optical assembly, length of the lens can be increased without sacrificing video capture system compactness and while maintaining a small protective dome diameter.
The folded optical assembly also allows the use of larger image sensors. This folded optical assembly can use image sensors of, for example, ⅓″ format, ½″ format, 1/1.8″ format, or larger, as well as smaller image sensors. There are at least two advantages for using a large sensor: The first advantage is the ability to use a large number of pixels on the image sensor creating a very high resolution image; The second advantage is the ability to use large pixels which collect light more efficiently with a better signal to noise ratio creating an image which is more clear. Large image sensors generally require large diameter lens optics, which in turn requires a relatively long lens length. As discussed above, folding the optical assembly as set out in embodiments of this invention allows the length of the lens to be relatively long without requiring an overly large protective dome for the video capture system. For example, some of the folded optical assembly embodiments discussed herein can provided a lens length at twice that of a conventional video capture system while retaining relatively small diameters, such as 1 inch to 2 inch diameters.
The folded optical assembly can have one or more moving lens groups or systems allowing focal adjustment for different object distances and lens focal length adjustments for different angles of view. These moving lens groups are translated along their own optical axis and thus require physical air space around the lens group to move within. Folding the optical assembly allows additional room for adding translatable lens groups without the need for a larger protective dome cover or increased system thickness.
Furthermore, the direction of view of the camera can be pointed within an entire hemisphere or sphere by rotating the lens about the video capture system axis and one of the optical axis directions. Rotation about a pivot point within the plane defined by the longitudinal axes of the optical paths is therefore not needed. For instance, in an embodiment of a security camera mounted on a horizontal ceiling that includes a single fold in the optical system, the lens can be rotated about the second optical axis direction which is normal to the image plane. This has the effect of changing the direction of view of the camera in a vertical direction.
In addition to rotating about an axis in the optical assembly for vertical image pointing direction, the entire video capture system can be rotated about an axis perpendicular to the plane of the mounting bracket. This operation will change the direction of view of the camera in a horizontal direction. Here, the dome of the video capture system can remain small by allowing it to rotate along with the rest of the video capture system. The image on the monitor will appear to shift up or down and side to side as expected with the rotation of the optical assembly.
With rotating limits of 90 degrees about the optical assembly lens axis and 360 degrees about the video capture system axis, all directions in the hemisphere can be observed. Allowing a rotation of up to 180 degrees about the optical assembly lens axis and 360 degrees about the video capture system axis will allow all directions in a sphere to also be observed.
The folded optical assembly can include one or more motors to adjust optical performance aspects of the lens. The use of these one or more motors allows the video capture system user to adjust, for instance, the lens focus distance, lens focal length, angle of view, and/or direction of view, remotely or without physically touching the lens. This allows the video capture system to remain compact since there is no need to allow the video capture system user to remove the cover of the video capture system and there is no need to allow finger-sized access points to control these lens performance aspects. Advantageously, the one or more motors enable greater ease of use, as well as compactness, of the video capture system.
Within the optical assembly, the direction of travel of the light is altered by an optical fold element 226, which in this embodiment is shown as an optical minor. In other embodiments, the fold element may also be a prism or other optical fold element. In this embodiment, only one fold element is shown in the optical path. However, in other embodiments two or more optical fold elements could be utilized along the optical path between the entrance and image sensor.
After received light is redirected by the fold element 226, it continues to travel through lens elements contained in the optical assembly along a second optical axis direction 230. This second optical axis direction 230 is parallel to the normal 232 to the plane of the image sensor and is substantially perpendicular to the initial optical axis direction 216. In other embodiments, the fold element 226 may fold the received light at an angle different than 90 degrees. In these embodiments, the second optical axis direction 230 may be angled from the initial optical axis direction 216 at an angle relative to the angle of the fold element 226. Here, the first optical axis direction 216 and second optical axis direction 230 intersect in the proximity of the optical fold element 226. In a typical security camera setup, the video capture system will be mounted on a level ceiling with a mounting plane 238 parallel to the ceiling.
Referring to
This first optical fold element 526 serves to redirect the light from a first optical axis direction 516 to a second optical axis direction 530, which is different from the first optical direction. The change in direction of the light can be between approximately 60 degrees and 120 degrees, although other fold directions are possible. A typical change of direction will be about 90 degrees. The intersection of the first optical axis direction 516 and second optical axis direction 530 is in the proximity of the first optical fold element 526.
The light will be then be transmitted through one or more additional optical lens elements 531 in the optical assembly 512 along the second optical axis direction 530. The light traveling along the second optical axis direction will next intersect a second optical fold element 556, which will serve to redirect the light along a third optical axis direction 558. The intersection of the second optical axis direction 530 and third optical axis direction 558 is in the proximity of the second optical fold element 556. Again the change of direction of the light due to the second optical fold element 556 can be between approximately 60 degrees and 120 degrees, although other fold directions are possible. A typical change of direction will be about 90 degrees.
The first optical axis direction 516 and second optical axis direction 530 form a first plane. Likewise the second optical axis direction 530 and the third optical axis direction 558 form a second plane. The first plane and second plane are shown as coincident planes in the embodiment illustrated in
The embodiments shown in
In addition, a second motor 884 may be attached to the folded optical assembly 812 in such a way as to cause one of the internal translatable lens groups 870 to be translated along its translation axis. In this illustrated embodiments, this translation is carried out by the rotation of cam 888 connected to a gear 890, which is attached to and driven by a second motor 884. In other embodiments, however, this translation can be accomplished by many different means. These one or more motors 884 that move the translatable lens groups can change the focal distance and/or magnification of the optical assembly.
The motor 880 to rotate the entire folded optical assembly 812 is shown with a shaft axis that is coincident with the optical assembly direction axis 830. However, this is not a requirement or limitation of the invention, as the shaft 882 of the motor 880 may be offset but parallel to the optical axis direction 830.
Some embodiments of the invention have been described above, and in addition, some specific details are shown for purposes of illustrating the inventive principles. However, numerous other arrangements may be devised in accordance with the inventive principles of this patent disclosure. Further, well known processes have not been described in detail in order not to obscure the invention. Thus, while the invention is described in conjunction with the specific embodiments illustrated in the drawings, it is not limited to these embodiments or drawings. Rather, the invention is intended to cover alternatives, modifications, and equivalents that come within the scope and spirit of the inventive principles set out in the appended claims.
This application claims priority to U.S. Provisional Patent Application No. 61/218,396, filed Jun. 18, 2009, entitled MICRODOME CAMERA, the contents of which are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61218396 | Jun 2009 | US |
