Comparison of a Fixed Lens and a Varifocal Lens Camera's FOV

[Perimeter]

I have seen several threads here in these pages comparing cameras of different types and different focal length.
Many comparisons assume tacidly that zoom setting number and focal length are linearly related and use a formula which assumes linearity to compute the dialed in focal length. But this does not have to be the case at all. Is there an official statement from Dahua that the zoom number relates linearly to focal length?

What I have been looking for but could not find is a simple table for the 5442T-ZE:
Zoom setting number vs vertical field of view ANGLE. That is the one table which needs no (hidden) assumptions but only a reference distance for focus. If you have enough data points in it, you could use linear interpolation for nearby angles without making big blunders.

Given such a table for your varifocal, if you like to know what a specific fixed lens will be able to cover, you just look up the vertical field of view ANGLE of that fixed lens in the spec sheet. (If that is wrong in specs, you better look for 30 day return policy)
Then you look up the zoom number that belongs to this angle on your zoom camera. Set the cam to this number and you got the vertical field of view of the fixed focal cam.

As a side effect, you get to check how accurate the specs for your zoom camera really are OR how precise you work OR how much tolerance there is.

I am actually considering to do just that, once the weather gets better. I am kind of curious...

 

[Fastb]

Interesting idea.
You say you'd

like to know what a specific fixed lens will be able to cover

The thing is, you don't have much choice in selecting a fixed lens for your camera. eg: 2.8, 3.6, 4.0, 6.0, 8.0, 12.0



If your calculations show you need a 3.25mm, that size lens isn't available in off-the-shelf fixed lens cameras.

That granularity in focal length isn't available to you - unless you choose a varifocal lens. Only then can you "dial in" the exact focal length your situation needs, based on real-world FOV. No fine calculations needed, really.
If I understand your objective is to pick the exact right focal length, you can do that. But the marketplace will only support specific sizes.

And remember, there's another real world variable to consider. Lens specifications are dependent upon on the size of the silicon sensor. ie: using the exact same lens in two cameras (with different size sensors) will produce two different size camera images. ie: different FOV.

All the above means consumers can simplify their camera selection by using a varifocal. (ignoring the impact on cam price)

Have fun,
Fastb

 

[Perimeter]

The thing is, you don't have much choice in selecting a fixed lens for your camera.

I don't want to get a fixed lens for my camera, I want to get another camera with a fixed lens in it. And I want to know what I will see with it before it gets here. (That was basically what the thread was about.)

All of your other arguments I try to circumvent with my method, as sensor size, lens mount etc will no longer matter.

My objective is to pick the exact right zoom setting number to emulate the field of view of a potential new camera with an existing zoom camera.

 

[tigerwillow1]

For selecting a fixed lens camera, I use a protractor and scissors to make cardboard cutouts based on the camera FOV specs, then take them out to the presumed camera location and carefully sight along the edges. Besides seeing what the FOV covers, this has also led me to change the camera location a few times. Not very high tech I realize.

 

[Perimeter]

For selecting a fixed lens camera, I use a protractor and scissors to make cardboard cutouts based on the camera FOV specs, then take them out to the presumed camera location and carefully sight along the edges. Besides seeing what the FOV covers, this has also led me to change the camera location a few times. Not very high tech I realize.

My idea is to get it done once and then have the zoom cam set right. Not because I hope to be at the right focal lenght but because I am at the correct viewing angle. You do it analogue, I want to do it digitally.

 

[wittaj]

If you are fast enough you can do it on this tool LOL

IPVM Releases Phone Version of Calculator

Thanks to everyone who uses and recommends the IPVM calculator! We have a new version that works on phones - no app install, just we optimized it with a responsive design for phones. Like the 'desktop' version, it is free for up to 4 cameras, with the same functionalities. If anyone has any...

ipcamtalk.com

 

[dudemaar]

I don't want to get a fixed lens for my camera, I want to get another camera with a fixed lens in it. And I want to know what I will see with it before it gets here. (That was basically what the thread was about.)

All of your other arguments I try to circumvent with my method, as sensor size, lens mount etc will no longer matter.

My objective is to pick the exact right zoom setting number to emulate the field of view of a potential new camera with an existing zoom camera.

There is an app for that. It gets you close.