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Jul 15, 2012, 03:18 PM
Dance the skies...
United States, MA, Walpole
Joined Dec 2003
19,012 Posts
Len A and Lens B FOV/AOV

I did my own calculations for the two lenses I have for testing... the std. lens ,now being called Lens A, and the new "red" lens, referred to as Lens B. To keep the terminology with a point of reference, I'm using FOV (field of view) as reference to the width of the native 16:9 camera image, and AOV as reference to the corner-to-corner dimension of the native camera image (like it or not!).

My method placed the camera 28.875 in. above the floor pointing straight down to take a picture of a tape measure running horizontally across the center of the frame. I did this with both Lens A and Lens B (see attached images). The lighting was not great, just natural light from a nearby window, but good enough for this exercise. Two things are apparent just by looking at the pictures: Lens A has less vignetting than Lens B... not surprising since wider AOV normally result in loss of brightness and focus. Also, the tape measure is not perfectly in the center, but close enough, and the Lens B camera may have been slightly out of vertical with some loss of focus on the left hand side, but again, close enough for this exercise.

So knowing the distance of the camera from the center of the image, the width of the image, and the fact that the width to height ratio of the image is 16:9, the image height can be calculated, and then appling a little geometry to get the diagonal distance and a little trigonometry to measure the FOV and AOV. I also attached my calcs for Lens A if anyone is interested.

Bottom line:

Lens A: FOV = 52.1 deg. & AOV = 58.6 deg.

Lens B FOV = 59.7 deg. & AOV = 66.8 deg. (my prior 5-10 deg. eyeball estimate was on target!)

I'll do the same for lens C and D when I get them.

You might be wondering why the stock Lens A has been called a 70 deg. AOV lens. That's the angle that was given to me as the manufacturer's designation, and is not necessarily wrong. In order to keep recorded images from showing some of the natural vignetting and distortion that is present in ALL simple lenses like these, the lenses need to project an image on the sensor that is larger than the sensor diagonal. A 70 deg. lens would give an image about 6 deg. beyond the captured frame corners... very reasonable to give a better picture quality.