2.8mm or 4mm help me

[i6jm]

I am confused between 2.8 and 4 and these are pictures of my house on the nature and from the maps I will install 4 cameras in each corner, Approx 4-6 meters high .
I want it to cover the entire green area that I identified in the pictures.
I bought DS-2CD2683G2-IZS(2.8-12mm) camera that has a Lens from 2.8 mm to 12 mm, but the camera when zooming does not show the numbers 2.8 and 4 mm etc. and I could not determine the appropriate Lens.




The four camera models that I will buy are DS-2CD2T87G2-

 

[Parley]

Without question, the 4mm in those areas. The 4mm has about 90 degrees of angle. Heck a 6mm might be better, depending on the view you want.

 

[Mike A.]

Regardless how common they are, rarely is 2.8 the right answer to this question.

 

[i6jm]

Regardless how common they are, rarely is 2.8 the right answer to this question.

You mean use a 4mm or 6mm lens?

 

[sebastiantombs]

Frankly, with them mounted that high you won't be able to identify, positively, anyone even with a 6mm. I'd suggest using and mounting varifocals down around two and a half meters and using the varifocal to zoom in to get positive identification. A varifocal typically goes from around 3mm to 12mm.

 

[Mike A.]

Generally so. Unless you want a cam only for very wide overview. Or, at the opposite end, if subjects will be very close (like within 10 feet or so). Otherwise, the 2.8 is going to be too wide to allow you to identify anyone.

Even if you don't have exact numbers, you should be able to reasonably approximate this with your current cam. All the way out will be 2.8. Halfway will be ~6. Somewhere between the two will be ~4mm.

ETA: I should have mentioned too that even if you had exact numbers, you'd still end up with only an approximation of the view since the field of view between cams at the same focal length may vary some. i.e., What you see at 4mm or 6mm or whatever from one cam to another may differ a little.

 

[sebastiantombs]

There's a converter in the WIki, in the blue bar at the top of the page, that will produce approximations of focal length based off the number displayed in the zoom setting of the camera.

Focal Length Calculator

Focal Length Calculator

Calculate the focal point of a camera to help determine the best size lens to order. Save & view your results later.

ipcamtalk.com

 

[Parley]

By the way your thread shows why a lot of us are waiting on a good varifocal camera with a 1/1.2" sensor to hit the market.

 

[i6jm]

Thank you all, I bought one camera with a 4mm lens because I never found a 2.8 lens in the local market, I will try it later and let you know

 

[i6jm]

By the way your thread shows why a lot of us are waiting on a good varifocal camera with a 1/1.2" sensor to hit the market.

Unfortunately, I was in a hurry to buy a Model DS-2CD2683G2-IZS, and its quality is rather weak at night due to my lack of experience, but after I found this forum, I benefited a lot.

 

[CCTVCam]

Listen to what Sebastian says. Mounting the camers high will just get you good pictures of someone's hair from the top or the top of their cap if wearing one. 2-2.5 metres is the ideal height. Rarely do cameras get interefered with and if mounting one on each corner, the cameras can probably cover each other. If height really is a concern, mount them as low as you can whilst out of reach to the average person. I personally wouldn't point them outwards because once people reach the building they are under the cameras fov and you will capture nothing - no damage or entry so proving it could be hard. I've always though the best way to cover a building is to point them, along the side so the majority of the view is away from the building but the building is still in at the side of the picture. That way you can capature most of what's out there but also what happens at the building. If you need a cameras looking further out, eg to cover that entry point on the front, just mount a 3rd one doing that.

 

[i6jm]

There's a converter in the WIki, in the blue bar at the top of the page, that will produce approximations of focal length based off the number displayed in the zoom setting of the camera.

Focal Length Calculator

Focal Length Calculator

Calculate the focal point of a camera to help determine the best size lens to order. Save & view your results later.

ipcamtalk.com

How does this tool work, when i zoom in Hikvision NVR it does not show any numbers only + -

 

[i6jm]

Listen to what Sebastian says. Mounting the camers high will just get you good pictures of someone's hair from the top or the top of their cap if wearing one. 2-2.5 metres is the ideal height. Rarely do cameras get interefered with and if mounting one on each corner, the cameras can probably cover each other. If height really is a concern, mount them as low as you can whilst out of reach to the average person. I personally wouldn't point them outwards because once people reach the building they are under the cameras fov and you will capture nothing - no damage or entry so proving it could be hard. I've always though the best way to cover a building is to point them, along the side so the majority of the view is away from the building but the building is still in at the side of the picture. That way you can capature most of what's out there but also what happens at the building. If you need a cameras looking further out, eg to cover that entry point on the front, just mount a 3rd one doing that.

The problem, my friend, is that the wires have been established at this height since I built the concrete building, but I will try to extend the wire outside to reach a height of 3 meters

 

[sebastiantombs]

The zoom number is available from the camera, not the NVR controls for the camera. I'm not an NVR expert, I use Blue Iris exclusively, but maybe one of our NVR folks can point you in the right direction to get to the camera directly from the NVR and bypass those controls on the NVR.

 

[The Automation Guy]

Listen to what Sebastian says. Mounting the camers high will just get you good pictures of someone's hair from the top or the top of their cap if wearing one. 2-2.5 metres is the ideal height.

Normally I would agree, but in this case the OP wants to monitor/capture footage of the street and has to shoot over a perimeter fence. If they mount the cameras at "normal" heights, they will only be able to monitor the courtyard and not the street.

 

[i6jm]

A model DS-2CD2T87G2-L 4mm was tested and placed in the window of the house temporarily, and at the weekend I will install it in one of the corners of the house.
I am notice that the colors and clarity of the model DS-2CD2T87G2-L(4mm) are much better than the model DS-2CD2683G2-IZS(2.8-12mm) set 2.8mm, is it because of the different lens?

Although the place for the two cameras is about 10 meters high, the model DS-2CD2T87G2-L(4mm) was able to distinguish the faces of the people and some of the license plates of the parked cars, again I do not know if it is because the lens is 4 mm or the model DS-2CD2T87G2-L(4mm) is has best specifications.


DS-2CD2683G2-IZS(2.8-12mm) set on 2.8mm

DS-2CD2T87G2-L(4mm)

 

[sebastiantombs]

The Fstop of a varifocal lens is generally higher than the Fstop of a fixed length lens due to the extra lenses needed to make it varifocal. That means it transmits less light through the lens because of those extra lenses. Focus can be fine tuned in the GUI of the camera if auto focus isn't working as well as it should be.

 

[i6jm]

The Fstop of a varifocal lens is generally higher than the Fstop of a fixed length lens due to the extra lenses needed to make it varifocal. That means it transmits less light through the lens because of those extra lenses. Focus can be fine tuned in the GUI of the camera if auto focus isn't working as well as it should be.

Thank you, so not because of specifications of Model DS-2CD2T87G2-L(4mm), but rather the multifocal cameras have weaker light than the fixed lens camera, this is what I understand

Another question, is this IPVM Designer / Calculator accurate?

This is what I concluded when I placed DS-2CD2T87G2-L(4mm) on my house on the map



But I don't understand what he means "Distance"، I put it 22 meters

 

[wittaj]

What he means is that many fixed cameras aren't really infinity focus - now some do a very good job at all distances, while others have a clear focus sweet spot distance and anything before or after that distance can be blurry.

The varifocal, while needing more light, has the ability to focus to your field of view.

 

[The Automation Guy]

Thank you, so not because of specifications of Model DS-2CD2T87G2-L(4mm), but rather the multifocal cameras have weaker light than the fixed lens camera, this is what I understand

Another question, is this IPVM Designer / Calculator accurate?

This is what I concluded when I placed DS-2CD2T87G2-L(4mm) on my house on the map

View attachment 141624

Yes. That calculator is pretty accurate in determining coverage and DORI distances. It's not perfect, but it is a very helpful tool. Of course this is a two dimensional diagram of a three dimensional space. As already discussed, how high you mount your cameras will have an effect on the type of footage you are able to capture that isn't well represented by the calculator. There is a section on the right side labeled "blind spot" and you should turn that on and enter the correct mounting height of your cameras. You might be surprised at what the camera won't capture near the camera.

What that diagram shows is that you will only be able to "identify" an unknown subject inside of your courtyard (the dark blue area). However given the height of the cameras, it will be capturing the tops of people's heads and you aren't going to get a good facial shot of anyone in your courtyard which will limit it's effectiveness. Honestly, cameras mounted at the height you are considering will not be effective for the courtyard at all due to this fact. If you want to capture footage in the courtyard, these cameras might be a good option, but they will need to be mounted 6-8' off the ground to work.

The next lighter blue band is the "recognize" distance. This means that you will likely be able to recognize a person that you already know out to about 1/2 into the street. Anything past that and you will have a hard time even recognizing someone - we call that the "observe" range. You can see people and what they are doing, but your footage isn't going to have enough detail to identity anyone.

If you need to "identify" people in the street, then you are going to need to look at cameras with a longer focal length (6mm or greater). Of course these cameras will cover less area, so you may need more cameras if you expect to cover 100% of the street.