On Thursday, 29 November 2012 at 13:43:46 +0800, RizThon wrote: >> 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. > > I feel like the full 180° *diagonal* angle of view from Olympus and the > 139.5° (as it's not specified it should be horizontal,
It's specified in the descriptions of other rebadged versions of this lens. Go to (for example) http://www.bhphotovideo.com/c/product/769514-REG/Rokinon_FE8M_O_8mm_Ultra_Wide_Angle.html and read: 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 The Bower badged lens is also available for Canon (APS-C). http://www.bhphotovideo.com/c/product/635178-REG/Bower_SLY358C_SLY_835C_8mm_f_3_5.html states: 180° diagonal angle of view on APS-C image format. > which is what is normally used) from Bower ends up being almost the > same (you computed for a fullframe fisheye 144°) Yes, but diagonal values look better for selling the product :-) >> 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. > > Each lens displays what it "sees", and there are usually distortions > compared to reality. So even with "normal" non fisheye / non very wide > angles, you have distortions. Those distortions are directly linked to the > way the lens is built, and thus different lenses with the same FOV will > have different distortions (even if they are not really noticeable). Did you read the article? It specifies numerous different projections. And the difference between 140° and 180° can't be attributed just to distortion. >> 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. > > For me a real fisheye lens should have at least a diagonal of 180° > for FF, or a full 180° circle for circular (or at least quite close > to 180°). It's possible that some vendors use the term fisheye just > because of the look of the pictures you can take. Clearly it's related to the projection. 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
pgp6dWjPXRutb.pgp
Description: PGP signature
