A fisheye lens is a lens with a viewing angle close to or equal to 180° (maybe greater than 180°). It is an extreme wide-angle lens, fisheye lens is its common name. In order to maximize the viewing angle of the lens, the front lens of this photographic lens has a short diameter and a parabolic projection to the front of the lens, which is quite similar to the eyes of a fish, so it is called a fisheye lens.
The shorter the focal length, the larger the viewing angle, and the stronger the distortion due to optical principles. In order to achieve or exceed the super-large viewing angle of 180 degrees, the designer of the fisheye lens has to make sacrifices to allow this kind of distortion to exist reasonably. As a result, except for the scene in the center of the picture, the other scenes that should have been horizontal or vertical have changed accordingly.
A fisheye lens is an optical imaging system with a large field of view and a large aperture. Generally, two or three negative meniscus lenses are used as the front lens group to compress the object-side large field of view to the field of view required by a conventional lens. For object point imaging with a large field of view, the beam hits the optical surface of the front lens group at a larger incident angle. After imaging by the optical system, the focus position in the meridian and sagittal planes may be completely inconsistent with the wavefront parameters. The exit angle is small. Therefore, a fisheye lens has the imaging characteristics of a plane symmetric optical system, but the aberration analysis of an axisymmetric optical system is not suitable for this.
Security cameras generally also use fisheye lenses. The imaging principle of fisheye lenses is different from that of ordinary lenses. It is not a one-time imaging. At the same time, the focal length is different from ordinary lenses, and the focal length of the fisheye lens will not affect the viewing distance and viewing angle. Nevertheless, the focal length of fisheye lenses used in security cameras is generally small. On the other hand, a fisheye lens camera cannot see too far, and is generally suitable for installation in a relatively narrow and enclosed space, such as the middle of the hall, the elevator, and the middle of the room.
Fisheye lens type
Fisheye lenses can be divided into round fisheye lenses and full-frame fisheye lenses due to the different image effects they present.
Lens angle
As mentioned earlier, the angle of view of the fisheye lens is not determined by the focal length, but is calculated and designed according to different projection mapping methods. Generally, the angle of view of a fisheye lens is designed to be 180°, of course, there are also 190°, 200°, etc. The largest fisheye lens on the market currently has a viewing angle of 280°. Considering the cost, design process and other optical alternatives, a fisheye lens with a larger viewing angle does not have much practical significance.
As described in the article “Lens of security camera”, the size of the target surface of the fisheye lens is best to be the same as that of the sensor, so that the best image effect can be obtained. The following figure shows several different matching effects of the lens and the sensor target surface.
1’ fisheye lens matching different target surface sensor renderings
2/3’ fisheye lens matching different target surface sensor renderings
The shorter the focal length, the larger the viewing angle, and the stronger the distortion due to optical principles. In order to achieve or exceed the super-large viewing angle of 180 degrees, the designer of the fisheye lens has to make sacrifices to allow this kind of distortion to exist reasonably. As a result, except for the scene in the center of the picture, the other scenes that should have been horizontal or vertical have changed accordingly.
A fisheye lens is an optical imaging system with a large field of view and a large aperture. Generally, two or three negative meniscus lenses are used as the front lens group to compress the object-side large field of view to the field of view required by a conventional lens. For object point imaging with a large field of view, the beam hits the optical surface of the front lens group at a larger incident angle. After imaging by the optical system, the focus position in the meridian and sagittal planes may be completely inconsistent with the wavefront parameters. The exit angle is small. Therefore, a fisheye lens has the imaging characteristics of a plane symmetric optical system, but the aberration analysis of an axisymmetric optical system is not suitable for this.
Security cameras generally also use fisheye lenses. The imaging principle of fisheye lenses is different from that of ordinary lenses. It is not a one-time imaging. At the same time, the focal length is different from ordinary lenses, and the focal length of the fisheye lens will not affect the viewing distance and viewing angle. Nevertheless, the focal length of fisheye lenses used in security cameras is generally small. On the other hand, a fisheye lens camera cannot see too far, and is generally suitable for installation in a relatively narrow and enclosed space, such as the middle of the hall, the elevator, and the middle of the room.
Fisheye lens type
Fisheye lenses can be divided into round fisheye lenses and full-frame fisheye lenses due to the different image effects they present.
- Round fisheye lens. The circular fisheye lens has a vertical viewing angle of 180°, and the horizontal and diagonal viewing angles are also 180°. The image sensor (sensor) is generally rectangular. According to the design, the image range covered by most round fisheye lenses is smaller than that of linear lenses. Therefore, the corners around the picture taken by the round fisheye lens with the rectangular sensor are completely black.
- Full frame fisheye lens. The fisheye lens enlarges the image circle to cover the entire sensor rectangular frame, which is called a “full-frame fisheye lens”. The diagonal viewing angle of the picture taken by this fisheye lens is 180°, and the horizontal and vertical viewing angles are both less than 180°.
Lens angle
As mentioned earlier, the angle of view of the fisheye lens is not determined by the focal length, but is calculated and designed according to different projection mapping methods. Generally, the angle of view of a fisheye lens is designed to be 180°, of course, there are also 190°, 200°, etc. The largest fisheye lens on the market currently has a viewing angle of 280°. Considering the cost, design process and other optical alternatives, a fisheye lens with a larger viewing angle does not have much practical significance.
As described in the article “Lens of security camera”, the size of the target surface of the fisheye lens is best to be the same as that of the sensor, so that the best image effect can be obtained. The following figure shows several different matching effects of the lens and the sensor target surface.
1’ fisheye lens matching different target surface sensor renderings
2/3’ fisheye lens matching different target surface sensor renderings
Last edited: