Learning About C-mount Lenses
C-mount lenses are special lenses, that are threaded male to fit into the female threads of a box style c-mount camera. Lenses come in all types of millimeter pieces both fixed and varifocal lenses. In the video surveillance world, the smallest lens is a 2mm lens. It is the widest shot you can get on the market. The lens sizes increase from there up to a 100mm or more. A relationship to remember when you are in the market of choosing the right lens is the field-of-vision to distance relationship. The future you want to see out, the bigger the lens is. On the contrary, a lens that is small like a 2.5mm lens will see a very wide angle-of-view, but distance is limited. One of the main reasons c-mount cameras do not come with a lens is due to nature of so many CCTV applications. No CCTV application is the same, so it is left up to the end-user to measure the dimensions of what they want to see and purchase the right lens for their c-mount camera. Most that are unsure will select a lens that is varifocal so they have some room to adjust the focus and zoom to get the right shot. In many cases varifocal lenses are becoming more and more popular. There are now varifocal lens that come in a 5mm to 100mm adjustment setting and some of them have powered DC auto-iris functionality too. All in all you will find many different lenses which will give you a very wide range of options, thus you are able to render the video you really want.
Typical C-mount Lens Formats
When figuring out how a lens works initially, it can be confusing to understand just what their purposes are and what they actually do. C-mount lenses consist of a few integrate parts that is responsible for producing their images. Lens format include focal length and aperture to determine the image a lens will capture. True lens format is the size of the CCD for the camera. There are many different formats, for example there are 1/2", 1/3", and 1/4" CCD chip-sets. Most c-mount cameras will have a 1/3" chip-set, thus making for an easy range of lenses to be compatible with. Not all lenses are made to work with certain chip-sets. For example, larger format lens are best used with c-mount cameras with smaller CCD chipsets. You need to always make sure you check the format of each lens before purchasing. They must format with the CCD or you will not have optimal video.
C-mount Lens Focal Length Concept
We were talking about this briefly earlier in this document about understanding how lenses work. Well focal length plays a huge role for many security camera system applications. Most CCTV applications have very unique problems and they are all solved differently. A very common problem is determining how wide of a shot you need. Most CCTV applications need to have very wide angle-of-views. To ensure you find a the right lens, you need to determine the dimensions of the area you want to see to be able to know what lens type you need. A rule of thumb is to go with the smallest lens millimeter size to get the widest shot. Focal length is the distance from the "principal point" of a lens to its focal point, expressed in millimeters (mm). Focal length controls the magnification of the image captured and the field-of-view. Again focal lengths can be fixed or varifocal. The shorter the focal length the wider the angle-of-view, the lower the magnification and the greater depth of field your video becomes. On the flip side, a longer focal length means you have a tighter angle-of-view, the higher the magnification, and the less depth of field you have.
C-mount Lens Aperture Concept
Aperture refers to the diameter of a lens's opening. It is a ratio relationship as well. The larger the lens opening, the more light enters the camera, which renders a very high quality of video. However with such a large aperture (lens opening) you have less depth of field. An example size for a c-mount lens with a large aperture is F1.2. Now a c-mount lens with a small aperture, will be a lens with a small lens opening. This produces a greater field of depth for your video shot. So know that a c-mount lens's aperture controls the amount of light and depth-of-field.
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