06-22-2009, 12:14 PM
A. The aspherical lens and the IR lens
Ashpherical Lens
The term “aspherical” describes the non-spherical shape of the lens. A non-aspherical lens has imperfect curvature, which can cause the corners of a picture to either appear unfocused or distorted. This is especially apparent with lenses with shorter focus lengths (hence at wider angles). The aspherical lens removes such an adverse effect from the lens.
Infrared (IR) Lens
In most environments, there exist three types of light: ultraviolet, visible, and infrared. The former is not recognized by the CCD camera, but both visible and infrared lights make an impact to the video. While the human eye cannot register infrared light waves, the CCD camera can and does convert it into light visible by the viewer through their monitor. Since visible and infrared are different types of lights, oftentimes they land on different focal points after travelling through the lens. This causes the final picture to become blurry as lighting condition changes.
An IR (infrared) lens is designed to achieve the ideal case, as seen on the right hand side of the illustration above. A special grade of coating is applied on the lens to allow more precise IR light passage, as well as allowing more light into the CCD. This means that both light waves will land on the CCD at the same location, giving the viewer a perfect picture. This type of lens is especially important when IR illuminators are used in conjunction with the camera.
The IR lens is also useful for cameras with and without the optical low-pass filter alike. The OLPF is designed to remove IR radiation to give truer colors. As explained earlier, both light visible by the human eye and the longer wavelength IR light are visible by the CCD. There also existsnear-IR light, which can penetrate the OLPF and give less ideal picture quality. The IR lens also forces such light to focus on the CCD, as it does with pure IR.
Due to the superior quality of these lenses, we only make recommendations of the aspherical IR lenses. For more information about the OLPF or lenses in general, please consult IP Surveillance 101 and IP Surveillance Deployment Guide on the ACTi website.
SUMMARY
B. What brands and lens types are recommended for use with ACTi cameras
Although there are countless types of CCTV lenses on the market at the moment, Tamron is arguably the top brand. It offers some of the best selections, as well as superior optics and excellent auto-iris responses.
Here are some general models we would recommend:
Ashpherical Lens
The term “aspherical” describes the non-spherical shape of the lens. A non-aspherical lens has imperfect curvature, which can cause the corners of a picture to either appear unfocused or distorted. This is especially apparent with lenses with shorter focus lengths (hence at wider angles). The aspherical lens removes such an adverse effect from the lens.
Infrared (IR) Lens
In most environments, there exist three types of light: ultraviolet, visible, and infrared. The former is not recognized by the CCD camera, but both visible and infrared lights make an impact to the video. While the human eye cannot register infrared light waves, the CCD camera can and does convert it into light visible by the viewer through their monitor. Since visible and infrared are different types of lights, oftentimes they land on different focal points after travelling through the lens. This causes the final picture to become blurry as lighting condition changes.
An IR (infrared) lens is designed to achieve the ideal case, as seen on the right hand side of the illustration above. A special grade of coating is applied on the lens to allow more precise IR light passage, as well as allowing more light into the CCD. This means that both light waves will land on the CCD at the same location, giving the viewer a perfect picture. This type of lens is especially important when IR illuminators are used in conjunction with the camera.
The IR lens is also useful for cameras with and without the optical low-pass filter alike. The OLPF is designed to remove IR radiation to give truer colors. As explained earlier, both light visible by the human eye and the longer wavelength IR light are visible by the CCD. There also existsnear-IR light, which can penetrate the OLPF and give less ideal picture quality. The IR lens also forces such light to focus on the CCD, as it does with pure IR.
Due to the superior quality of these lenses, we only make recommendations of the aspherical IR lenses. For more information about the OLPF or lenses in general, please consult IP Surveillance 101 and IP Surveillance Deployment Guide on the ACTi website.
SUMMARY
- Aspherical lenses reduce improper diffraction of light by precise lens curvature.
- Aspherical lenses rarely generate unfocused corners, and reduce image distortions at wide angles.
- IR lenses allow more light into the camera, essentially lowers the aperture level.
- IR lenses make sure IR and near-IR light are aligned with visible light on the CCD, making it useful for OLPF and non-OLPF cameras alike.
B. What brands and lens types are recommended for use with ACTi cameras
Although there are countless types of CCTV lenses on the market at the moment, Tamron is arguably the top brand. It offers some of the best selections, as well as superior optics and excellent auto-iris responses.
Here are some general models we would recommend:
