On Thursday, 29 November 2012 at 16:02:03 +0800, RizThon wrote: >> Ultra wide-angle 8mm fisheye lens with exaggerated perspective and >> approximately 180° angle of view, for dramatic effects >> >> Ultra-wide 139.3° diagonal field-of-view for 4/3 size image formats > > Of course if you use the same lens with different sensor size, the result > will be different. That's why the Nikkor 10.5 on a small sensor has a 180° > diagonal while on a fullframe sensor the HFOV is around 180°.
I seem to be having difficulty making myself clear. My apologies. To spell it out: - The Olympus 8 mm lens, designed for Four Thirds sensors (21.63 mm diagonal), covers an angle of 180° along this diagonal. - The Samyang (I think that's the original manufacturer), also 8 mm, covers an angle of 139.3° along this same diagonal. And as I said, the difference in angle can't be explained by distortion alone. >> Did you read the article? It specifies numerous different >> projections. And the difference between 140° and 180° can't be >> attributed just to distortion. > > Indeed: > "The angle of view of a fisheye lens is usually between 100 and 180 degrees[ > 1] <http://en.wikipedia.org/wiki/Fisheye_lens#cite_note-bare_url_a-1> while > the focal lengths <http://en.wikipedia.org/wiki/Focal_length> depend > on the film > format <http://en.wikipedia.org/wiki/Film_format> they are designed for." That wasn't what I was referring to, but arguably it needs to be improved. The reference is barely authoritative, and "Film format" sounds positively archaic. I was referring to section 3, http://en.wikipedia.org/wiki/Fisheye_lens#Mapping_function which discusses the projections and gives a reason for the big differences in angle. > At least now you should have a better idea whether or not you want > that fisheye lens! I don't see any input to that decision from this discussion. > I have a fullframe fisheye and it's quite practical to only take 6 > pictures horizontally (I have a pano head so I also take a zenith, > but I always have issues stitching the nadir, as the shot is > handheld to avoid seeing the tripod). Indeed. I've taken the coward's way out and done without a nadir, so looking straight down shows a black hole. Greg -- Sent from my desktop computer. Finger [email protected] for PGP public key. See complete headers for address and phone numbers. This message is digitally signed. If your Microsoft MUA reports problems, please read http://tinyurl.com/broken-mua
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