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"Neil Harrington" <> wrote in message
news: ...
>
> "Savageduck" <savageduck1@{REMOVESPAM}me.com> wrote in message
> news:2010081011344922503-savageduck1@REMOVESPAMmecom...
>> On 2010-08-10 11:14:04 -0700, Shiva Das <> said:
>>
>>> In article <>,
>>> "Neil Harrington" <> wrote:
>>>
>>>> "Shiva Das" <> wrote in message
>>>> news:shiv-
>>>> .com...
>>>>> In article <crednS_gOehk4P3RnZ2dnUVZ_g->,
>>>>> "Neil Harrington" <> wrote:
>>>>>
>>>>>>>
>>>>>>> And by perspective I mean what Albrecht Durer, Johannes Vermeer,
>>>>>>> Leonardo da Vinci, and Michelangelo Buonarote meant by perspective:
>>>>>>> the
>>>>>>> geometrical reconstruction of a stationary point of view looking at
>>>>>>> an
>>>>>>> image projected on a stationary picture plane (in the case of Durer
>>>>>>> a
>>>>>>> glass plate, in the case of Vermeer a Camera Oscura).
>>>>>>
>>>>>> Obscura, I assume you mean.
>>>>>>
>>>>>
>>>>> You may assume what you wish. I meant exactly what I said: Camera
>>>>> Oscura. Brush up on it here -- I hope you read Latin:
>>>>>
>>>>> http://www.uniurb.it/Filosofia/bibli...oza/camera.htm
>>>>
>>>> I don't. I also don't read Italian, which is what that text appears to
>>>> be
>>>> in. But in any case, the illustration in that article is of a camera
>>>> obscura. (With a "b.")
>>>>
>>>>>
>>>>>
>>>>> And since you have amply demonstrated that you do not understand the
>>>>> first thing about perspective, I will bow out of this waste of time of
>>>>> a
>>>>> discussion.
>>>>
>>>> You are probably wise to do so. You might want to instead spend the
>>>> time
>>>> brushing up on the difference between Latin and Italian.
>>>
>>> Now you are seeing the letter "B" where it isn't. The page has the word
>>> "Oscura" six times and the word "Obscura" zero times.
>>>
>>> 'Nuff said.
>>
>> You are taking "oscura" from an old latin document,
>
> I think he's taking it from a document in Italian, not necessarily old.
>
>> and it may well have been the correct term when that document was
>> drafted. However check; < http://en.wikipedia.org/wiki/Camera_obscura >
>> and I think you will find your usage is the "obscure" and less commonly
>> used one.
>
> Yes indeed, though it still may be commonly used among Italians.
>
>

So we have obscure and obsolete translations & definitions of obscura,
rooted in Latin, Greek & Italian, depending upon your linguistic
orientation.


--
Peter

"Neil Harrington" <> wrote in message
news: ...
[]
> 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_o...ra_obscura.asp

Cheers,
David

"Neil Harrington" <> wrote in message
news: ...
[]
> 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
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

David J Taylor <david-> wrote:

> "Neil Harrington" <> wrote in message
> news: ...
> []
> > 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_o...ra_obscura.asp
>
> Cheers,
> David

I visited one in Tavira, Portugal last year. The operator/guide was an
english chap.

--
Andy Templeman <http://www.templeman.org.uk/>

"David Ruether" <> wrote in message
news:i41jlu$i18$...

[...]
> YEAH!!! Judge Williams has just
> followed up his ruling declaring Prop. 8 in California unconstitutional with
> a judgment that his own stay on implementation will be of very limited
> duration.

A BIG Oooopser above! That was Judge Walker, not Judge Williams!
--DR

"Paul Furman" <paul-@-edgehill.net> wrote in message
news ...
> 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/l...tive_types.htm
>> http://www.donferrario.com/ruether/l...erspective.htm
>> http://www.donferrario.com/ruether/s...erspective.htm
>> http://www.donferrario.com/ruether/l...tion_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=...+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/l...erspective.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

"Paul Furman" <paul-@-edgehill.net> wrote in message
news: ...
> Neil Harrington wrote:
>> "Paul Furman"<paul-@-edgehill.net> wrote in message
>> news ...
>>> David Ruether wrote:

[Answering "NH"...]
>>>>> 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!

>> But that doesn't solve it at all, Paul. Again: if you take a very wide-angle
>> shot of the distant horizon, with nothing else in the scene to lend
>> perspective, then there is NO perspective no matter how wide the "angle of
>> view" is. (Everything is at infinity for all practical purposes.) And
>> because there is no perspective, someone looking at the photo has no clue as
>> to whether its "angle of view" is wide, normal or narrow.

Neil is still confusing angle of view, distance, subject characteristics,
image "look", etc. with perspective. But, in his narrow example, it is
true that the characteristics of various lens perspective types would
likely not show (unless the lens were pointed up or down relative
to the horizon, especially with a lens of fisheye type, and/or the subject
foreground contained detail, hard to avoid....

> Yep. Near the center angle, it doesn't matter much. Using a fisheye lens, you can put a person in the middle of the frame (with a
> little distance) and they look perfectly normal.

Yep!

>> Only when objects are reasonably close *and* three-dimensional do you get
>> perspective. Your drawing of a half-sphere that you linked to is a good
>> example of this. The half-sphere's surface at the corner of what would be a
>> very wide-angle photo shows the apparent distortion you'd get with a very
>> wide-angle lens. But the sections of the half-sphere, being flat, are still
>> round because they are two-dimensional.
>
> Right. And those same sections would appear as ovals once you turn the lens toward them because they are no longer parallel to the
> rectilinear projection (perpendicular to the axis of the lens).

Yep, again! As with tilting a photo relative to our visual axis...

>>> http://www.google.com/#hl=en&source=...+angle+of+view

>>>>>> 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:

Ahem! NOT "distorted" if you are strict about definitions! Although it may
look "unfamiliar"...

>>>>>> http://www.donferrario.com/ruether/l...erspective.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 [Paul] 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.

>> Right. And those differences are the stuff of which perspective is made.

> On further thought, perspective has two properties: distance and angle. The word 'viewpoint' might encompass both. I agree that
> changing the angle changes the perspective.

No. Perspective is NOT a subject characteristic (nor any other characteristic),
but it is ONLY a lens/imaging-type characteristic!

> I learned to draw isometric in high school drafting class then perspective in college: 1 point, 2 point and even 5 point fisheye
> perspective constructed on paper with a 3D grid and vanishing points. When you get into macro beyond 1:1, it's not uncommon for
> some lenses or lens combinations to exhibit reversed perspective where the vanishing point is behind you, or a telecentric lens
> where there is no vanishing point. For telecentric, you can only capture an image as wide as the front element of the lens. Long
> telephoto perspectives come close.

I cover some of these in my articles... And, as you point out with
the above, these *perspective types* have individual characteristics,
and names...
--DR

"Paul Furman" <paul-@-edgehill.net> wrote in message
news ...
> 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/l...tive_types.htm
>> http://www.donferrario.com/ruether/l...erspective.htm
>> http://www.donferrario.com/ruether/s...erspective.htm http://www.donferrario.com/ruether/l...tion_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=...+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/l...erspective.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

"Paul Furman" <paul-@-edgehill.net> wrote in message
news: ...
> Neil Harrington 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.

>> 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...

>>> The word 'viewpoint' might encompass both. I agree that changing the angle
>>> changes the perspective. I learned to draw isometric in high school
>>> drafting class then perspective in college: 1 point, 2 point and even 5
>>> point fisheye perspective constructed on paper with a 3D grid and

>> That 5 point fisheye perspective is something I'd like to see an example of.
>> The term sort of boggles my mind.

> http://kurtssketchbook.blogspot.com/...rspective.html

This appears to me to have a single vanishing point...

>>> vanishing points. When you get into macro beyond 1:1, it's not uncommon
>>> for some lenses or lens combinations to exhibit reversed perspective where
>>> the vanishing point is behind you, or a telecentric lens where there is no
>>> vanishing point. For telecentric, you can only capture an image as wide as
>>> the front element of the lens. Long telephoto perspectives come close.

>> 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.

> Well, it's not really relevant and was intended just for mind blowing <g>. But telecentric lenses are used for industrial
> measurement scopes. The light rays simply are gathered parallel from the front element so you can measure objects with depth
> accurately and there's no parallax errors. Focusing doesn't cause enlargement changes.

A good example...

> Reverse perspective, I believe is only a property of how the out of focus areas are rendered when stopping down so you couldn't do
> focus stacking and get that result. There is only ever one little slice in focus and the rest of the image is interpolated by
> shrinking the OOF circles. I probably explained that wrong but it's not all that unusual when using reversed lenses and various
> combos beyond 1:1.
>
> Here's a full explanation:
> http://www.janrik.net/PanoPostings/N...allaxPoint.pdf

??? 8^)
--DR

"Paul Furman" <paul-@-edgehill.net> wrote in message
news:7dWdnSTwUdo-...
> David Ruether wrote:
"NH" wrote:

>>>> That 5 point fisheye perspective is something I'd like to see an example of.
>>>> The term sort of boggles my mind.

>>> http://kurtssketchbook.blogspot.com/...rspective.html

>> This appears to me to have a single vanishing point, [not 5...].

> Hmm, it is actually drawn wrong somewhat. The arcs should meet the other 4 points, or the points should be marked further off the
> page. I'm not sure I really understand the grids on this page but it shows it:
> http://nanarealm.blogspot.com/2008/0...rspective.html

This site makes some points I have also made about our seeing
in spherical (fisheye) perspective, but I disagree about the use of
the term barrel "distortion" - and the "5-point perspective" still makes
no sense to me in reference to spherical perspective... This site, at
http://www.scottmcdaniel.net/drawing...e/5_point.html
a l m o s t "gets there", but maybe not quite...

>>> Reverse perspective
[...]
>>> Here's a full explanation:
>>> http://www.janrik.net/PanoPostings/N...allaxPoint.pdf

>> ??? 8^)

> LOL, yep. I did actually grind through that whole thing once and sort of got it. The aperture selects rays when stopping down and
> if the aperture isn't in the correct position, it'll select the wrong rays and misrepresent things.

Hmmmm.......
--DR