Researching security cameras online is an exhausting endeavor. It is difficult to identify the difference between cameras when bombarded with a list of dozens that appear the same (Further Reading: CCTV Lens Guide: Choosing a Security Camera Lens). Pricing is what stands out to the average user and it may not always be clear why there is a large price difference between two similar cameras. Brand and country of origin play a big part in a unit’s price, but the specs of a camera are very important. Most companies list products and their specifications using vocabulary words and industry terms that are not common knowledge to most consumers. I think we (CCTV salespeople) are guilty of doing that as well. Today, I want to write about the difference between monofocal and varifocal lens, but first I should define what those words mean.
Basically every camera needs a lens. Lens focal length, which determines the field of view and zoom, is measured by millimeters. The smaller the number of mm, the wider the angle of view will be. Transversely, the larger the mm the narrower the field of view, and the picture will be zoomed into a smaller area, like looking through binoculars. For box cameras, a lens is a separate interchangeable piece that is sold separately. For all dome and board cameras, the lens is built into the camera and is part of the spec sheet for the camera. Monofocal lenses will also be called “fixed” lenses. Whatever the focal length , the important thing to know is that it only has one setting. A varifocal lens has multiple focal lengths. In regular terms, it means that the lens can zoom in and out, manually. Monofocal lenses for box cameras come in many focal lengths, but for cameras with built-in lenses, most either have a wide angle monofocal lens or a varifocal lens. If you want a dome camera with an 11mm lens you will probably have to buy a varifocal dome to get it.
In the real world, it works like this. If you buy a camera with a 3mm lens and put it up, you are stuck with that field of view. That is not always a bad thing. For a small room or any area in which a wide angle is needed, a fixed 3mm camera will be fine. If you put it up and realize that you want a tighter image or want to zoom into an area, then you are out of luck.
Freedom to Adjust
With a varifocal lens, you have more freedom. Now for the varifocal lenses I am writing about, there will be two adjustments. One will zoom the lens in and out and one will focus it. The focal length and focus must be set by hand at the camera. If you get a camera with a 2.8 to 12mm lens, you can adjust to focal length to any number between 2.8 and 12. That means that you don’t need to have a precise measurement of the lens needed but simply a general idea. Once the camera is installed and you realize you want a 7mm lens, all you need to do is adjust it to 7mm. This is the same for any length between 2.8 and 12mm. So if you need 8 cameras, one with a 7mm, one with a 10mm, one with a 3mm, etc., just get 8 varifocal cameras and adjust them to the right focal length during the install. Another plus is the ability to adjust the lens for different applications. For example imagine a store owner buys a camera with a 2.8 to 12mm lens. When he installs it originally he sets it to 2.8mm which is gives him a wide angle of the register area. Then he has a problem with theft. He then adjusts the camera all the way to 12mm to zoom in on the register. The same camera in the same place was used for different purposes at different times.
Size of Range
What to look for when buying a varifocal camera is the size of the range. A lens with a 4 to 9mm lens has fewer options than a 3.5 to 16mm lens. Also make sure that you have a good idea of what you want to see and with how much detail (Check our Lens Calculator). It is a weird question to ask because I know we want to see everything with perfect detail but that is not realistic.
I hope this helps explain a little bit about lenses and what to look for when designing a system. Please give one of our salespeople a call if you have any questions, they are happy to work with you to pick the right camera and accessories.