is the field of vision on 2.8mm lens and 3.6mm the same on 720p cameras?

yeahman

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Hi,
I have ordered a 720p IP camera with 2.8mm on aliexpress but I received the 720p camera with 3.6mm instead.

I contacted the seller and he replied me by saying FOV on 2.8mm is the same as 3.6mm on 720p camera.

Is this true or he is lying to me??
 

nayr

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that is not true; but in nearly all cases 2.8mm sucks ass so you got lucky.. its far too wide to see detail at any reasonable distance.. its rarely finds an approprate use, and its almost always indoors.

Camera Calculator / Design Software <-- learn to use this awesome tool
 

yeahman

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but I chose the 2.8mm because I want a wider angle FOV... I don't really need to see long distance
 

nayr

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you get fisheye warping of horizontal lines that distorts the image; its usually wider than 90 degrees.. and im not talking long distance, they struggle to see detail further than a few feet away, espically at 720p
 

yeahman

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hmm ok so I should keep the 3.6mm lens then?

is 2.8mm on 1080p cameras better?
 

nayr

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you should at least try it and see how you like it IMHO, yeah its a bit better with 1080p..

Play with: Camera Calculator / Design Software and keep PPF > 100 to maintain the ability to identify faces.. the more pixel density the more detail (generally, in practice more megapixels does not always mean more detail due to different sensors photon capturing capabilities)

720p 2.8mm drops below 100ppf beyond 7ft away... 3.6mm is beyond 9ft away.
1080p 2.8mm drop below 100ppf beyond 8ft away.. 3.6mm is beyond 11ft away.

All things being equal, a 3.6mm 720p will have more detail than a 2.8mm 1080p.. just barely tho.

Indoors 3.6mm often gives you nearly a 90 degree FOV which can see an entire room when mounted in the corner, Outdoors most people are far better off with 6-12mm optics if your targets are typically 15-35ft away.. almost never are wide angle lenses worth a shit for any security purposes.
 
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yeahman

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ok so you recommend that I keep the 3.6mm lens .. was going to open a dispute
 

Masejoer

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"I contacted the seller and he replied me by saying FOV on 2.8mm is the same as 3.6mm on 720p camera." - that is a blatant lie. Focal length and field-of-view will depend on sensor size, not resolution. Other numbers don't mean anything.

is your shot wide enough? If not, get the seller to fix their mistake, and pick up a 2.8mm lens camera. It's as simple as that. Nayr is playing with numbers to show that because you get a wider shot at 2.8mm, you also lose detail from subjects further away from the camera - they will be on fewer pixels. Higher resolution simply lets you get more detail in the scene, potentially allowing you to go wider on the focal length.

Picking up detail is all about filling the frame with the subject. You choose your focal length for that. In general, 2.8mm works great for watching an area, but 6mm+ (up to 100mm or higher) is useful for catching details (license plates, faces, etc) of a subject when they pass through that area. Backyard gates and doors are areas where longer focal lengths (more zoom) can be beneficial. As you can imagine, it can be good to have one longer-focal-length camera for every wide angle camera you have. Gather a lot of views with more detail (6-12mm can work well), and also pick up the general area with wide-angle to see everything that occurs. That or install 20x 6mm cameras on just the front of a house - catch all the detail, one narrow field-of-view at a time.
 
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