We have made choosing the right lens for your camera easy. There are many factors to consider when selecting the correct lens for your application. Use this easy to follow lens guide to make the correct choice for your CCTV Cameras.
Fixed Iris- CCTV security cameras that are used in good and constant light conditions (e.g. indoors with electric lighting) will perform satisfactorily with a "Fixed Iris Lens". Fixed Iris lenses with fixed focal length are the least expensive and the most widely used.
Fixed lens cameras have a set field of view and cannot be manipulated to produce a wider or narrower angle. These lenses are generally found as 3.6mm, 4.3mm, 8mm, 12mm, etc.. The higher the number of the focal length, the more telephoto the effect, and the narrower the angle of view.
Manual Iris - In constant light conditions that are either dim or very bright, a "Manual Iris Lens" may be the answer. As its name implies, this type of lens can have the Iris aperture adjusted by hand to give the optimum camera image quality. Pricing for "Manual Iris" lenses is higher than Fixed Iris and lower than Auto Iris lenses.
Auto Iris - In varying light conditions (e.g. outside or inside facing a window) the iris on the camera will need to open and close to accommodate changes in light intensity, otherwise the camera images will be too bright or too dark. Lenses with electrically powered irises which automatically adjust as light conditions change are called "Auto Iris Lenses". They are more expensive but do a much better job in varying light conditions.
DC powered Auto Iris – This function is basically used to amplify or reduce light for a lens to obtain a more defined picture view for the camera. Use of such a camera and lens outfit can dramatically improve performance in lower lux conditions. You can often spot such a setup by seeing a cord between the back of the camera body and the lens itself. It is there to provide a means to deliver the DC voltage to the circuitry inside the lens. You cannot simply attach such a lens to any camera- even if the mount is a perfect fit. DC auto iris lenses require voltage and, therefore, a camera with a compatible DC output. This is why it is recommended that you purchase a lens and camera together from our company.
Variable focus (or vari-focal Lens) - Allow the user to modify the field of view from its widest/ most panoramic to the narrowest and most telephoto views that it is capable of. Some lenses provide a 4-8mm (widest at 4mm and most telephoto at 8mm), whereas others may provide 5-50mm for a super zoom in ability. Many are set up to interface with a variety of optional lenses. However, there are also cameras with built-in lenses that cannot be removed or replaced. The removable lens cameras are referred to as "C" or "CS" mounts because those are the type and size which are security industry standards. Many lens choices are available and the decision should be based on actual requirements for the application.
Focal Length- The focal length of a lens is usually given in Millimeters (mm). Focal lengths of most CCTV camera lenses vary from 3.6mm to 16mm for fixed focal length lenses, to well over 70mm for zoom lenses. So what does that mean? In general, short focal length lenses (e.g. 4mm) have wide fields of view. This is good for close-ups or for seeing a large area. Objects appear smaller, rapidly, as distance from the camera increases. As lens focal length increases, the field of view narrows and more distant objects are easier to define.
If, for instance, you wanted to be able to positively identify people, 25' away from a camera, a short focal length lens (e.g. 3.6mm) would give such a large field of view (37'x 26') that recognition would be uncertain. An 8mm or even 12mm lens would be far better.
It is important to use the right lens for the light conditions and desired field of view; otherwise the images seen and recorded will not be satisfactory. CCTV security cameras with an integral lens are less expensive but do not offer lens choices and are therefore limited in their usefulness.
How to select a proper security camera lens in 3 easy steps
1. Should I use Manual Iris, Auto Iris or DC lens?
- You can save money and use manual iris lens only when scene illumination never changes. Example: illuminated store or office. If the light changes a lot it is recommended using auto-iris.
2. What focal length lens do I need?
- Hint: The smaller the focal length number => The wider the field of view.
- If you have security camera in the office or warehouse and you want to see as much as you can, you should go for 2.8 or 4 mm lens (makes wide, somewhat distant view)
- If you want to observe limited area, like entrance you should go for 8mm or (makes narrow view and objects are closer).
3. Use vari-focal lenses to get flexibility for choosing best field of view.
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