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Old Dec 29, 2012, 12:53 PM
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Camera vs. lens AOV

Quote:
Originally Posted by KillerCut View Post
So the #16v1 and #16v2 both with a D lens would have 120degree fov?

how come this site:
http://www.chucklohr.com/808/C16/

says the #16 has 90degrees with the D lens
and the #16v2 has 120degrees with the D lens?

I have a feeling that the sensor chip is slightly different, but the lenses are the same... So shouldn't I get 90degrees fov on the #16v2 (which has live output) if I were to swap sensor chips between the two?
No, there is no difference in sensors. This keeps coming up, including just recently. A thread search will find all the posts, but the bottom line is people use AOV to mean different things.

The lens has an angle of view that is fixed, and it's used by the lens manufacturers to tell a developer the (conical) angle the lens is physically capable of capturing. This is critical to a camera designer since this image cone must be at least big enough to cover the image sensor shape the camera is trying to record. And that shape (e.g. the 16:9 aspect ratio image the #16 camera captures for HD recording vs the 4:3 aspect ratio image the #16 camera outputs in the composite video output signal) are different. A lens that can only project an image that just barely covers the corners of the 4:3 image will not be able to fully cover the corners of the wider 16:9 image.

So the lens AOV is what it is... fixed and definitive. And it has to be big enough to at least cover the corner-to-corner distance of all the image sizes a camera intends to capture. But that is still not enough for a good quality image!

Inexpensive lenses can have a significant light drop off (vignetting) the further the portion of the image is from the center of the lens axis. Also, it's common for the focus to become less sharp on the sensor array (which is flat) the further the image gets from the lens center. This is because the lens focal plane (where the image is sharp) is NOT flat like the sensor array, but rather is slightly curved, like the surface of a sphere. So for these reasons, to get a very bright and sharp image with consistent color across the entire captured image frame (corner-to-corner!), the lens AOV in these inexpensive cameras must be considerably greater than captured image size to crop off those bad image portions. This is one key thing that defines a good camera from a poor one.

Then aside from the lens AOV comes the different meaning of AOV to different people. Many consider it to mean the side-to-side view angle of the image the camera actually captures. You'll see this in many posts here. And as mentioned above, even that can be different for the same camera and same lens for different aspect ratio images!

The problem is there is no consensus definition for what just the term "AOV" means for a camera. It's necessary to specify what is being referenced when speaking of AOV.

So, it can be correct to say, for example, the lens has a 120 deg. AOV as the ads say, and for an image to have a 90 deg. side-to-side AOV for the same camera with the same lens! AOV for a camera could also be stated in terns of top-to-bottom, or corner-to-corner AOVs, and each of those will be different for a 16:9 image vs a 4:3 image for the same camera with same lens!

Hence all the confusion!
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Last edited by Tom Frank; Dec 29, 2012 at 04:08 PM. Reason: added title and made a FAQ
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