Variable Lens

[jwadsley]

What is the purpose of a variable lens in a camera? What does it do for quality, detection, etc?

I see a lot of Amcrest cameras with 2.8MM and then then there are variable lens cameras....don't understand the difference...

 

[sebastiantombs]

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 want 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.

 

[jwadsley]

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.

So a Varifocus lens would be useful for a gate or a driveway where you know someone is going to be. Otherwise a fixed 2.8mm lens is better for covering a wider area just "to see what is out there"?

If I understood your explanation correctly, it was a fantastic explanation!

 

[sebastiantombs]

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.

 

[jwadsley]

Why would a camera show it in degrees instead of mm?


Motorized Varifocal Lens 57°-106°

 

[jwadsley]

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.

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?

 

[sebastiantombs]

Just a guess, because, for some reason, they don't want to reveal what the actual focal length range is. The example you cite I'd approximate at ~4mm to 10 or 12mm

 

[Mark_M]

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.

Varifocal (VF) is like a PTZ camera without the panning and tilting, it can just zoom with physical lens moving.

To the example above, lets say you have a large farm and want to manage a gateway. Why would you have a wide angle lens when it only needs to focus on that one part.
You may think a wide lens captures more area, but that loses detail (like faces and number plates).

Varifocal comes in two types, motorised and manual. Manual means you set it on the camera and motorised means the camera can change automatically.

I really haven't seen a decent scenario for a lens needing to automatically zoom in/out during the day.
You could have it capturing a wide view and then zooming onto a gate at night, but why?
CCTV is all about capturing the detail needed and there's no way to get detail unless it's recorded. Better to have more cameras than one trying to fit the place of two.

 

[sebastiantombs]

I've seen the chart in many posts, but don't have it at my fingertips right now. It's simply a chart showing approximate distances for identification, recognition and so on.

 

[Mark_M]

Why would a camera show it in degrees instead of mm?

Motorized Varifocal Lens 57°-106°

Example; I'm wanting to purchase a camera to place in the corner of a room. Walls are at right angles (90°).
So I could buy a camera with a 2.8mm lens which has a view of 90°. That would see the whole area with no blind spots.

 

[wittaj]

To identify someone with the 2.8mm lens that is popular, someone would have to be within 13 feet of the camera, but realistically within 10 feet after you dial it in to your settings.

My neighbor was bragging to me how he only needed his four 2.8mm fixed lens cams to see his entire property and the street and his whole backyard. His car was sitting in the driveway practically touching the garage door and his video quality was useless to ID the perp not even 10 feet away.

Here are my general distance recommendations, but switch out the Dahua 5442 series camera to the equivalent 2MP on the 1/2.8" sensor or equivalent Hikvision works as well.

• 5442 fixed lens 2.8mm - anything within 10 feet of camera OR as an overview camera
• 5442 ZE - varifocal - distances up to 40-50 feet (personally I wouldn't go past the 30 foot range but I like things closer)
• 5442 Z4E - anything up to 80-100 feet (personally I wouldn't go past 60 feet but I like things closer)
• 5241-Z12E - anything from 80 feet to almost 200 feet (personally I wouldn't go past 150 feet because I like things closer)
• 5241-Z12E - for a license plate cam that you would angle up the street to get plates up to about 175 feet away, or up to 220 with additional IR.
• 49225 PTZ - great PTZ and in conjunction with an NVR or Blue Iris and the cameras above that you can use as spotter cams to point the PTZ to the correct location to compliment the fixed cams.

You need to get the correct camera for the area trying to be covered. A 2.8mm to IDENTIFY someone 40 feet away is the wrong camera regardless of how good the camera is. A 2.8mm camera to IDENTIFY someone within 10 feet is a good choice OR it is an overview camera to see something happened but not be able to identify who.

Main keys are you can't locate the camera too high (not on the 2nd story or above 7 feet high unless it is for overview and not Identification purposes) or chase MP and you need to get the correct camera for the area trying to be covered. A 2.8mm to IDENTIFY someone 40 feet away is the wrong camera regardless of how good the camera is. A 2.8mm camera to IDENTIFY someone within 10 feet is a good choice OR it is an overview camera to see something happened but not be able to identify who. Also, do not chase marketing phrases like ColorVu and Full Color and the like - all cameras need light - simple physics...

 

[sebastiantombs]

Thanks @wittaj

 

[Flintstone61]

Thanks to wittaj…now i have buy more Cameras

 

[sebastiantombs]

Found this one which might help, too, Keep in mind this is approximate and varies based on sensor size. -

 

[looney2ns]

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.

 

[jwadsley]

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.

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.

I've already read the cliff notes and still had questions....I appreciate the responses posted here for the additional insight

 

[biggen]

What additional questions do you have that weren't answered in the above posts?

 

[jwadsley]

What additional questions do you have that weren't answered in the above posts?

I got them answered in this thread....

 

[Rob2020]

Out of curiosity, why don't you like Blue Iris? I did not see anything in the thread to explain your hesitance.

Before I found Ipcamtalk, I read all kinds of horror stories, CPU runs at 80 - 100% all the time, learning curve makes it unusable, only liked by the fanboys at Ipcamtalk, etc

Based on the recommendations here I bought BI and I have found Blue Iris to be affordable, rock solid, and easy to use, I have yet to have any issues and even with my Ryzen 2700 Processor I have yet to hit 15% CPU with 4 cams recording 24/7. I don't have a dog in this fight but all the Ipcamtalk recommendations (BI, EmpireTech, etc) I have followed have done me well.

 

[Flintstone61]

I was liking Blue iris over Eye MAx PC's software which, along with an Intel Celeron, Plain Jane mid tower, I was told, " And here's the Security System",,,,
Wheres the guy keying a White Hundai Sonata. (Hint, it's in the 1st pic) Pretty horrid security system in place at the Condo in 2017. ... I'm very busy with other tasks and haven't got much time to tweak settings on BI....So I like that the DVR's need less attention,
But when it comes to scrubbing thru video, and finding incidents quickly.... Gotta Love BI......Until I figured out that my Jidetechs were making BI unstable, I wasn't feeling too "in love with it, I wanted to Love it, but It kept fritzing out over the weekends, until I learned more about the hardware and software I was doomed to mediocre results.
Now I've been stable for a couple weeks and trusting BI. I still like that 15 of my 26 Cameras are also being recording to XVR's and Dvr's.....But I hate searching the timelines on them,
I've come a long way Baby!!!