Perspective (was Re: Has ultrawide angle become an overused cliche?)
in [Digital Cameras]
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From: David Ruether on 13 Aug 2010 08:09 "Paul Furman" <paul-@-edgehill.net> wrote in message news:xLydnf4ncKnVEPnRnZ2dnUVZ5rGdnZ2d(a)giganews.com... > David Ruether wrote: >> as I have pointed out earlier, with ever narrower angles of view, ALL the >> several perspective *types* approach each other in appearance. You ["NH"] are confusing the "look" of a photograph with the >> definition of "perspective", >> and leaving out defining "angle of view". For more, see -- >> http://www.donferrario.com/ruether/lens_perspective_types.htm >> http://www.donferrario.com/ruether/lens-angle-of-view-and-perspective.htm >> http://www.donferrario.com/ruether/seeing_and_perspective.htm http://www.donferrario.com/ruether/lens_distortion_types.htm >>> This seems like mostly an argument about semantics but here's an example that supports the idea of real differences in wide >>> angle 'perspective'. >> Um, best to correct that to "angle of view"...;-) > OK, "angle of view" is a better term. Semantics solved! :-) > http://www.google.com/#hl=en&source=hp&q=site%3Adonferrario.com+angle+of+view 8^) >>> > Take a pic with a super-wide, then crop the*corner* of the image. Now try to reproduce that perspective with a telephoto >>> > lens. It >>> > could be accomplished with a stitched pano, if the stitching software stretches things but not without software distortion. >>> > >>> > Check the drawing on the bottom of this page, of a distorted sphere in the cropped corner of a wide angle view: >>> > http://www.donferrario.com/ruether/lens-angle-of-view-and-perspective.htm I don't think that could be reproduced with a >>> > telephoto lens. >>> > Put a striped ball on the left side of your desk and try it. >> Thanks for that drawing for my article.;-) It also clearly shows that within >> planes parallel with the sensor plane (with rectangular perspective) that >> there is no "distortion" no mater how wide the angle of view is. > Well, there is distortion in the egg shaped silhouette of the sphere because it's at the far corner of a super-wide. If you swing > the same lens around to center the sphere, it'll have a round outline again. The topographical lines parallel to the image plane > are perfect circles though. More than this is that the axes running through the parallel-plane-cut sections of all the hemispheres are on the vanishing lines/point for the rectangular perspective, so there really is no "distortion", although there may be "unfamiliar visual effects due to viewing 3D objects imaged near the edges of a wide angle of view" since the "stacking" of their sections on the off-axis vanishing lines will cause offsets that change the overall shape of the 3D object... --DR
From: Neil Harrington on 13 Aug 2010 09:39 "David J Taylor" <david-taylor(a)blueyonder.co.uk.invalid> wrote in message news:i42mfl$nm6$1(a)news.eternal-september.org... > "Neil Harrington" <nobody(a)homehere.net> wrote in message > news:v_6dnZGdNcTKA_nRnZ2dnUVZ_sOdnZ2d(a)giganews.com... > [] >> I don't know about Greek, and I don't know whether "camera oscura" is >> still current in Italian. But it is still called a camera obscura today, >> within the last few decades there were still several in operation and my >> guess is they still are. They are fascinating devices in the modern form, >> and at least one was built in a rotating tower so that it could scan a >> good part of the local town That one used a reflex system which projected >> the image down onto a large flat table. > > We have one locally in Edinburgh, for example: > > http://camera-obscura.co.uk/camera_obscura/camera_obscura.asp > > Cheers, > David Yes! Remarkable! I'd never heard of that one.
From: Neil Harrington on 13 Aug 2010 09:46 "David J Taylor" <david-taylor(a)blueyonder.co.uk.invalid> wrote in message news:i42mrc$ol0$1(a)news.eternal-september.org... > "Neil Harrington" <nobody(a)homehere.net> wrote in message > news:i_qdnRQSpt9vU_nRnZ2dnUVZ_tWdnZ2d(a)giganews.com... > [] >> Can you explain that a little more? Or direct me to a source? I'm having >> a problem grasping that "reversed perspective" and "telecentric" >> business. It looks very interesting but I'm really floundering here. > > See: > http://en.wikipedia.org/wiki/Telecentric_lens > > For digital use, the idea is that the rays from the lens hit the sensor at > a vertical angle of incidence, thus reducing the variations in the image > due to any variations of the sensor with angle of incidence. Some Yes, that principle I'm familiar with. > manufacturers claim their lenses are "telecentric", but whether they > actually work any better in a system I don't know. A pointer to > comparative tests would be helpful. > > Cheers, > David Thanks for the link, David. It's something I'm going to have to read over carefully before I really understand it.
From: Neil Harrington on 13 Aug 2010 16:37
"Paul Furman" <paul-@-edgehill.net> wrote in message news:7dWdnSTwUdo-EvjRnZ2dnUVZ5oednZ2d(a)giganews.com... > David Ruether wrote: >> Paul Furman wrote: >> >>>>> On further thought, perspective has two properties: distance and >>>>> angle. >> >> No! See my post, above (or read some of it in "PF's" post, since >> you "plonked" me (and I see your posts also only in "PFs" posts...;-). >> Again, "perspective" is defined by the lens perspective type, and >> by NOTHING else. This is confusing. David seems to be addressing me, but he's replying to a statement by you. >> >>>> Also shape and size, I would say. Just distance and angle perhaps if >>>> you're >>>> only considering the relationship of viewer to subject(s), but shape >>>> and >>>> size as well if you're considering the image itself that's shown in >>>> perspective. Again, your drawing of the half-sphere being an example of >>>> this. Or any photo of reasonably close three-dimensional objects, >>>> especially >>>> when taken with short lenses. With long lenses there is what I think >>>> it's >>>> reasonable to call a loss of perspective, as the photo approaches >>>> (though it >>>> can never reach) the character of an isometric drawing. >> >> I have pointed out that last a few times before - that within ever >> narrowing >> angles, the appearance of the various lens types approach each other, but >> do not ever really become the same. The perspective is defined by the >> type the lens makes use of, and nothing else, contrary to your opinion. >> But it does look like you [NH] are making progress...;-) Nothing has changed in my opinion about any of the above, so DR's seeing my "progress" here seems to be his developing understanding of my position. I am going to un-plonk David to make this discussion easier. If I can figure out how to do that. There must be a list of killfiled people here somewhere but I don't think I've ever taken anybody off it before. . . . Dang, I hope I haven't just plonked Paul. [ . . . ] |