The purpose of a vaible focal length is to allow adjustment of the focal length at the time of installation to best suit the location and purpose of the camera. Not every camera should be a "wide field of view" camera as nice as that may look to most people. With a 2.8mm lens if you ant to actually identify someone, that someone needs to be within about ten feet of the camera. A varifocal lets you set exactly what you need rather than settling for a 2.8, 3.6 or 6mm and is typically a 12mm maximum focal length.
There are two downsides to varifocals. They are more expensive than a fixed lens. There is a slight loss of light due to the additional optics. IE it need a little more light than a fixe lens.
A varifocal is designed to be set and left at a specific focal length. It is not a true zoom lens.
All I saw in the wiki in the blue bar was a lot about Blue Iris, which I have no intention of using....Can you post a link to the material in question about lenses?A lot of people will buy a varifocal camera first. Then set it up with a test rig, bucket of stones or sand, a 2x4 and a long network cable, to test each camera location and figure out what fixed focal lens will work best for each proposed camera location as well as to test those locations. There is a calculator here which will convert the "zoom" number into mm so an approximate focal length can be determined.
I'll caution you about those wide, sweeping views. With a 2.8mm at a distance, you may be hard pressed to figure out what is happening. 3.6mm is a wide view, IMHO, and that makes it hard, at times, with things that happen further out.
Have a look in the Wiki, in the blue bar at the top of the page. There's a ton of excellent information in there regarding camera selection and lens selection. Running out and buying a "kit" usually ends up in disappointment when the rubber meets the road, and wasted time, effort and money. Video surveillance is not as simple as it's made out to be on TV and in the movies. When you zoom in, digitally, on a video it will pixelate at 2x magnification with no way to magically clear it.
Varifocal (VF) is like a PTZ camera without the panning and tilting, it can just zoom with physical lens moving.The purpose of a vaible focal length is to allow adjustment of the focal length at the time of installation to best suit the location and purpose of the camera. Not every camera should be a "wide field of view" camera as nice as that may look to most people. With a 2.8mm lens if you ant to actually identify someone, that someone needs to be within about ten feet of the camera. A varifocal lets you set exactly what you need rather than settling for a 2.8, 3.6 or 6mm and is typically a 12mm maximum focal length.
There are two downsides to varifocals. They are more expensive than a fixed lens. There is a slight loss of light due to the additional optics. IE it need a little more light than a fixe lens.
A varifocal is designed to be set and left at a specific focal length. It is not a true zoom lens.
Example; I'm wanting to purchase a camera to place in the corner of a room. Walls are at right angles (90°).Why would a camera show it in degrees instead of mm?
Motorized Varifocal Lens 57°-106°
That seems to be the common answer around here just like using Blue Iris seems to be the end all be all, for me its not.In the Wiki, read the Cliff Notes, on a real computer, not a smart phone, it's all there, you just have to do a bit of reading.
Buy once cry once.
I got them answered in this thread....What additional questions do you have that weren't answered in the above posts?