Subscriber Discussion

How To Calculate Hfov With Viewing Angle?

Hi, I would like to know how to calculate the horizontal field of view (ft /m) considering horizonal viewing angle. For example, there are two cameras both are: CMOS 1/4", Focal 2.8, and f-stop 2.0. Though, horizontal viewing angle is 66 and 80 degrees and resolution supported are SVGA and 1.3Mp

How does the resolution affect the viewing angle?

Undisclosed, There lies the crux of another discussion I started. I can't understand how you can get different HFOVs out of two cameras that use the same size imager and the same focal length lens unless one of the cameras doesn't use the entire width of the imager. It's just not possible since HFOV is a function of imager size and lens focal length, no matter the pixel count.

A lot of manufacturers use the same imager in different resolution models. For instance, in this SVGA vs 1.3MP case, they probably both use a 1.3MP imager. On the SVGA model, the manufacturer simply crops the extra pixels, thus reducing the FoV.

Now, you may ask, if you are already using a 1.3MP imager, why even sell an SVGA model? This is typically a price segmentation issue, offering a small discount for more cost conscious buyers.

Great! With that in mind and getting back to the original question, how do you calculate FOV if the manufacturer doesn't release data regarding what part of the imager they use, just the imager's size?

Well John, there's something else to add to your camera tests: spec vs. actual measured FOV :)

As per Theia's Lens Calculator, on changing the resolution the view angle changes while keeping other parameters constant

But as per their paper

HFOV = Camera Dist * Chip Width / Focal Length

Taher, that equation is true presuming the manufacturer uses all the pixels. As such, it's better to think of it as a maximum. If they crop it obviously it is going to be a narrower FoV. The alternative to cropping and dropping those pixels is to simply encode at a stream resolution lower than the sensor resolution. That will maintain the max HFoV.

As for testing this, I am still not convinced this is a big practical problem?

I could see it being a practical issue if a dome is marketed as wide angle, for example, with a 110° FOV, and out of the box it's 89°. But I really doubt that's the case. I'd like to think that manufacturers aren't crazy enough to make those claims. I'd like to think.

It is, if the Installer typically pre-calculates lens requirements based on manufacturers' published focal length and imager size (like us). If you can't count on the published specs, or don't trust them (regarding the Axis 3000 series), how do you determine what to buy if FOV is critical (again, our case).

I goes along with many analog camera manufacturers publishing diagonal FOV - a useless spec.

On a similar note, I need to find a new lens calculator. It is simple to calculate lens requirements based on a 1/3" or 1/4" imager when you measure the HFOV and distance to the camera. Not so when you consider the greater variety of modern camera imager sizes (1/1.8", 1/2.5", 1/3.6", 1/5" and 1/6" and the more standard 1/4", 1/3" and 1/2").

Carl, the Theia calculator has quite a number of imager size options.

That calculator doesn't work the way I want. As far as I can tell, you can't plug in sensor size, distance and desired FOV numbers and have it calculate the lens focal length required.

Carl, you can select "Other Lens" from the lens dropdown, and it will give you a slider from 2.5mm-60mm - the FOV will change realtime as you slide it, so you can just adjust focal length until you see the FOV you want. Not EXACTLY what you're looking for, but should do the job.

Yeah, and I could use a 12" ruler to measure the 12' distance between the camera and the table but why would I? :>o

Welllll... at least the Theia calculator doesn't require getting up off yer arse ;)

This one lets you select sensor size, distance to target, and width of target area, and will provide lens length... it only has 1/4, 1/3 and 1/2 sensors, but for oddball sizes, you can always go one size larger, which will give you a slightly wider FOV for a given lens, then either accept the extra area, or guesstimate the proper lens from there. If nothing else, it will give the minimum focal length you need, and you can go for a varifocal that covers that.

Could try Pelco's as well: Pelco Field of View Camera Lens Calculator - select sensor, then provide two of three factors (FOV, lens length, or distance) and it gives you the third.

JVSG's calculator lets you play with a lot of different parameters, including mounting height, tilt angle, required PPF, etc.

At least the Theia calculator shows the same HFOV, no matter the sensor's resolution pixel count. Exactly what I determined with my trusty Rainbow lens calculator:

  • 1/3" sensor
  • 12' distance
  • 6' HFoV
  • = 10mm

Hi All I found a site Angular Size Calculator which lets you put in the measurments of Width x Distance to calculate the angle of Fov. By doing this we could get the FOV required then work out what lens and camera combo would come close to the the area we want to cover. What do you think?

Well, it works! but it is extremely rudimentary. You then need to take result (in degrees) to another calculator to figure out the focal length (in mms). Yes/no?