Ken, I get the same results from the Theia calculator. We'll ask Vivotek for comment.
We actually had a similar thread asking about other camera's FoV width calculation, with equally confusing results!
Thanks John. I believe we have shared a formula with you that I found quite helpful but wanted to post it.
d = horizontal size of sensor
f = focal length
Seems that this is pretty accurate as long as you have the dimensions of the sensor.
The challenge with the formula Ken lists and most basic tools is that they don't work for fisheye and 'fisheye-like' lenses or any lens designed to view close to or beyond 90 degrees. Those lenses come with some optical distortion at the edges but those edge regions then also receive a non-linear projection of the field of view so a little bit of additional sensor gives a lot of additional angle of view.
Also the calculation is affected by the aspect ratio of the sensor.
A 2mp 16:9 sensor is wider than a 4:3 sensor of equivalent diagonal dimensions.
Did your calculations assume a 4:3 or 16:9 sensor?
My calculations assumed both Bohan. It impacts the vertical FOV angle but not the horizontal.
This calculator allows you to switch the aspect ratio and see the difference in FOV angle. Although you cannot chose a true 1/2.7" because they do not have the option, one can make an educated decision given the calculations for sensors that are 1/2.5" and 1/3".
Maybe you can weigh in on this John.
Unless Vivotek is willing to publish the sensor model used the actual size of the sensor may well be different to that on the spec sheet. We have discovered this issue with more than 1 world Top 20 manufactuer.