Alley in Pisa, Italy

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I am trying to create a DIY wide angle webcam with the goal of maximizing my horizontal and vertical fov. I'm thinking that I need to use fisheye filters and then defish the video afterwards. Is this worth the hassle vs just getting a wide angle filter?

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This appears to be a question about videography specifically, as opposed to photography. Have you looked to ask this on the Audio-Video Production site? –  John Cavan Aug 2 '13 at 10:40
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also, is half a long piece of string longer than a short piece of string? –  Matt Grum Aug 2 '13 at 13:33
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This is probably an example of a video question where it's exactly the same for stills. –  mattdm Aug 2 '13 at 14:13
    
@mattdm - which is why I just commented. Mind you defishing video is probably harder. –  John Cavan Aug 2 '13 at 18:30

1 Answer 1

The field of view would be the same as an equivalent focal length, but fish eye can go wider than a flat lens. There is only so much distortion you can remove however. By nature of the way the light paths travel, there is going to be some roundness to the image. It's the same problem as projecting a round globe on to a flat map. You can distort the image to make it appear less rounded, but this actually decreases the accuracy of the image because the angle that things were photographed from was not flat, it was rounded. This means that on the edges, you will be making it look like you are looking forward at things you were actually looking sideways at.

It's also worth noting that even non-fisheye wide angle lenses do a certain amount of this effect as well, it is simply projected differently.

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I have no idea what you mean by "By nature of the way the image is sampled, there is going to be some roundness to the image" or "this actually decreases the accuracy of the image because the angle that things were photographed from was not flat, it was rounded". There is a 1:1 correspondence between a rectilinear and fisheye image. Also it is not possible for any defishing or other 2D image transformation to make it look like something was photographed from the front when it was side on to the camera. That be magic. –  Matt Grum Aug 2 '13 at 14:55
    
@Mattgrum - the edges of a fisheye image deform and stretch, in theory you can perform a deformation that will make it look less bowed, but it would distort things from how they actually appear. Sampled was a bad word though, the light paths from a fish eye are coming in near perpendicular, thus they aren't photographing the front of the object, but the side. I took defishing to simply mean correcting for the high degree of lens deformation in the image that makes it appear spherical. You can make it look more flat, but things still appear distorted since perspective is all wrong. –  AJ Henderson Aug 2 '13 at 15:32
    
It's the classic round globe on flat map problem. You can change the projection, but it still looks funky. –  AJ Henderson Aug 2 '13 at 15:32
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The point is you can take a fisheye image and transform it into an image that is exactly how the scene would have appeared had you used a (well corrected) rectilinear lens (apart from different resolution). If the way things appear in this image (which is not "wrong" just different) is not what you want, then you can chose not to defish, or apply a different projection... –  Matt Grum Aug 2 '13 at 16:03
    
@Mattgrum - right, I should clarify that I mean to say that a fisheye can go to a wider field of view than a flat lens since it can capture light coming in perpendicularly. I should clarify on that. I didn't understand what you were saying in your last comment until I reread the question. –  AJ Henderson Aug 2 '13 at 16:07

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