On Thursday, 29 November 2012 at 10:29:19 +0800, RizThon wrote: > 2012/11/29 Greg 'groggy' Lehey <[email protected]> > >> Partially. The 9 mm has: >> >> Horizontal FOV: 87.73° >> Diagonal FOV: 100.49° >> Vertical FOV: 71.68° >> >> I don't have a formula for fisheyes, so I can't give the output of my >> program, but I'm told that it has 180° on the diagonal. Being a >> fisheye, this *should* mean (on a 4:3 aspect ratio) a horizontal FOV >> of 144° and a vertical FOV of 108°. That's a long way from the 9 mm. > > There can indeed be a big difference between a 9mm rectilinear lens > and an 8mm fisheye lens, even if 9 doesn't sound that far from > 8. It's also possible to have fisheyes from different vendors with > different mm, even if they are all fullframe or circular.
Indeed. This is what has been puzzling me. There are two different 8 mm fisheyes available for Olympus: the relatively expensive 8 mm f/3.5 from Olympus, and the 8 mm f/3.5 from various rebadgers (Bower, Samyang, Rokinon). The former costs about $800 and has a full 180° diagonal angle of view. The latter costs about $300, and from the specs state an angle of 139.3° on Four Thirds. From what I've read it will only give a full diagonal 180° on APS-C cameras. http://www.bhphotovideo.com/c/product/880776-REG/Bower_sly358od_8mm_f_3_5_For_Olympus.html Since my last message I've been reading a bit about fisheyes, and it seems that, like Hugin, there are various projections. http://en.wikipedia.org/w/index.php?title=Fisheye_lens&action=edit§ion=12 gives some information, though I'm still trying to digest it. At least one of the images appears to show a horizontal angle of more than 180°. If anybody knows more details, I'd be interested. >> I also get the same results whether I select "full frame fisheye" or >> "circular fisheye". What's the difference? > > I find it weird that it gives the same result... > > A fullframe fisheye gives you an image corresponding to the biggest > rectangle (because your sensor is a rectangle) in a circle, that's why the > diagonals are 180°, but horizontal and especially vertical won't be > as much. OK, and that's what the Olympus is. But there's the implicit assumption that *somewhere* there's a 180° angle. That's clearly not the case for some lenses. 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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