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I was looking for a webcam that shows a wide area left and right of me, so I compared the field of view of several webcams.

I was under the impression that a greater number as the FOV angle means that one can see more. To verify this, I looked up the specs of the Logitech C160 and C310 which I both own. I found that the C160 has a field of view of 50° while the C310 has 60°, so one would think that the C310 shows a bigger area of the wall behind me.

Since this is contrary to what I had said from gut feeling, I did a little experiment. I set both cameras next to each other facing a sheet of graph paper.

camera setup

Then I looked at the picture from the webcam and marked the edges of the image with a pen on the paper (click for original resolution).

results (click for original)

I found that in the C160 (field of view = 50°) I can see 21.6 cm of the paper and in the C310 (field of view = 60°) I can see only 19.2 cm.

To see the marks for the C160 in the C310 I have to move the C310 further away by a full 3 cm.

This makes no sense to me, can someone clarify what "field of view" actually means?

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The focal length of the lenses on the units seem to be different. It is also possible that the sensors are different sizes. If you can determine the sensor size you should be able to do the math on it yourself and see if the quoted angle of view's were correct or not. –  dpollitt Jul 8 '13 at 1:37
    
The focal length given in the datasheets I linked confuses me as well. –  AndreKR Jul 8 '13 at 1:51

2 Answers 2

up vote 2 down vote accepted

Field-of-view is the angular extent shown through the lens. For fixed-lens cameras, and all web-cams that I know of, the field-of-view is normally stated relative to sensor-size. This is very reasonable since the lens is fixed and cannot server on something else.

While this sounds like numbers could be compared, there several reasons why not:

  • Field-of-view can be measured vertically, horizontally and diagonally. Those numbers are not the same but some manufacturer only quote one of them and do not say which one. If you have to guess, it is usually the diagonal field-of-view.
  • Field-of-view changes with focus. As a lens focuses, there is often change in its field-of-view, particularly when close-focusing. Most field-of-view numbers are stated with the lens focused at infinity. Actually, even the focal-length changes when away from infinity! Unfortunately, there is no formula for what happens to field-of-view as focus is changed because it depends on the particular optical design of the lens.
  • Field-view varies with aspect-ratio. On cameras that shoot with different aspect-ratio, a reduced field-of-field is possibly shown. Only a few makers special field-of-view by aspect-ratio. A common example is switching between SD (4:3) and HD (16:9) video but the same thing applies with image-formats (3:2, 4:3, 1:1, etc).
  • Digital processing reduces aspect-ratio. Certain features reduce the displayed aspect-ratio to save some boundary pixels used in their computation. This is always the case for electronic stabilization and most often used for multi-shot techniques like Multi-Frame Noise-Reduction, and HDR plus geometric corrections such as distortion correction,
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It turned out that the given field of view does only apply for higher resolutions, when I open the C310 device to capture 320 x 240 (like Skype did in my first test) it changes it's field of view. I guess the reasoning was to get a better resolution on the subject which is assumed to be in the middle. –  AndreKR Jul 8 '13 at 2:39

Field of View refers to the breadth of the field (the region of a real-world scene that is "visible" by the imaging medium. The angle for a given field of view can be determined a few ways. It can be measured horizontally, vertically, or diagonally. In a general sense, most people think of the FoV in terms of the horizontal, but that is not necessarily what is actually measured for a given product like a web cam.

It should also be noted that the Field of View is not purely determined by the lens' focal length...it is also affected by the sensor. Sensor shape and size can affect the angle. Assuming a 4.4mm focal length, a larger sensor is going to support a wider field of view, where as a smaller sensor will constrict the field of view. Sensor area may even remain constant, however if the shape of the sensor changes, that too will change the field of view. A wide sensor will have a larger FoV, where as a square sensor with the same area will have a smaller FoV (again, assuming a horizontal angular measure).

Given the specs of the two web cams you linked, I think there is very likely some typos or just sloppy data entry work. A 40cm focal length for the C160 makes no sense, especially when the C310 has a mere 4.4mm focal length. I suspect it is more likely that the C160 has a 4.0mm focal length, which would indeed mean it has a wider field of view, if the two cameras use the same sensor.

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