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wide angle lense distortion (objects appear larger at the ..

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April 7, 2005 10:05:08 PM

Archived from groups: rec.photo.digital (More info?)

In theory, objects that are the same size and the same distance away from
the lense should appear on the photo the same size, right?

That doesn't seem to be the case with wide angle lenses. If I just stand
still and pivot the camera (i.e. keeping the same distance to all objects in
the frame), the same object would appear larger when passing near the edge
of the frame. Is this a bug or a feature?

This distortion makes it difficult to stitch photos of interior shots of a
room, which is what I want to do. I have seen people try to do this and the
resulting photo looks bad because you can sense where the edges of the
original frames are (objects are bigger there).

Are there wide angle lenses that does not have this distortion? Alternately,
is there a program/plugin that could correct this distortion?
April 7, 2005 10:05:09 PM

Archived from groups: rec.photo.digital (More info?)

I had a tough time stitching really wide angle shots but the better
stitching programs should be able to do it. Panotools did, Autostitch
did not.


I guess if you don't want that distortion, the other option is fisheye
where lines aren't straight & things up close in the middle are over-sized.

peter wrote:
> In theory, objects that are the same size and the same distance away from
> the lense should appear on the photo the same size, right?
>
> That doesn't seem to be the case with wide angle lenses. If I just stand
> still and pivot the camera (i.e. keeping the same distance to all objects in
> the frame), the same object would appear larger when passing near the edge
> of the frame. Is this a bug or a feature?
>
> This distortion makes it difficult to stitch photos of interior shots of a
> room, which is what I want to do. I have seen people try to do this and the
> resulting photo looks bad because you can sense where the edges of the
> original frames are (objects are bigger there).
>
> Are there wide angle lenses that does not have this distortion? Alternately,
> is there a program/plugin that could correct this distortion?
>
>
Anonymous
April 7, 2005 10:09:50 PM

Archived from groups: rec.photo.digital (More info?)

Think of the path that the light has to follow and you will see what is
happening. The cure is to turn the camera on its side and shoot your
panoramic that way...and don't go any wider than necessary. Overlap by
50%....stichers do better with more overlap.


"peter" <nospam@nospam.com> wrote in message
news:o De5e.3363$ox3.2082@trnddc03...
> In theory, objects that are the same size and the same distance away from
> the lense should appear on the photo the same size, right?
>
> That doesn't seem to be the case with wide angle lenses. If I just stand
> still and pivot the camera (i.e. keeping the same distance to all objects
in
> the frame), the same object would appear larger when passing near the edge
> of the frame. Is this a bug or a feature?
>
> This distortion makes it difficult to stitch photos of interior shots of a
> room, which is what I want to do. I have seen people try to do this and
the
> resulting photo looks bad because you can sense where the edges of the
> original frames are (objects are bigger there).
>
> Are there wide angle lenses that does not have this distortion?
Alternately,
> is there a program/plugin that could correct this distortion?
>
>
Related resources
Anonymous
April 7, 2005 11:29:09 PM

Archived from groups: rec.photo.digital (More info?)

peter <nospam@nospam.com> wrote:
> In theory, objects that are the same size and the same distance away from
> the lens should appear on the photo the same size, right?
>
> That doesn't seem to be the case with wide angle lenses. If I just stand
> still and pivot the camera (i.e. keeping the same distance to all objects in
> the frame), the same object would appear larger when passing near the edge
> of the frame. Is this a bug or a feature?
>
If you make a big enlargement and view the picture from
the centre from a distance equal to the focal length times
the enlargement ratio, the picture will then appear in
correct perspective.

When you take a picture, you are mapping a section of
a sphere (the scene viewed from one point in space)
onto a flat surface. The normal way of doing this is
called rectilinear perspective which is based on the
idea that keeping straight lines straight is important.
The inescapable consequence of keeping straight lines
straight is that objects get enlarged towards the edge
of the picture. Since the exact opposite size distortion
happens when you view the picture from the centre at
a distance equal to the focal length times the enlargement
factor, everything looks right again.

One other approach which can sometimes work well is the
cylindrical perspective offered by swing-lens panoramic
cameras. In cylindrical perspective, vertical lines are
kept straight, but horizontal lines towards the top
and bottom of the frame are curved. The relative sizes
are correct from left to right, and since the panoramic
photograph does not show much to the top and bottom,
you do not notice any size distortion in that dimension.
If you are stitching pictures together to create this sort
of panorama, you would normally have each picture take
up a rather small horizontal angle. It should be possible
to mathematically transform a wide angle rectilinear view
into cylindrical perspective, but I don't know enough
about image editing to help you.

The problem is essentially the same as that of making
a flat map of the world show all countries in the right
shape. You have to decide what aspects you wish to distort
when you map a spherical surface onto a plane.

Peter.
--
pirwin@ktb.net
Anonymous
April 7, 2005 11:30:25 PM

Archived from groups: rec.photo.digital (More info?)

In article <oDe5e.3363$ox3.2082@trnddc03>, peter <nospam@nospam.com> wrote:
>In theory, objects that are the same size and the same distance away from
>the lense should appear on the photo the same size, right?

Not if you want to keep straight-lines as straight lines in your image.
Fundementally, the image of the world that you see is curved - you can't
represent that accurately on a flat surface. Something has to give - it's
the same problem that cartographers have.

>Are there wide angle lenses that does not have this distortion?

Yes, they're called "fisheye lenses". They preserve relative area by
distorting angles instead.

Some scenes (I find group portraits and lots of landscape stuff) look much
better with a fisheye lens, I find. Others (typically scenes with lots of
straight lines in, such as architectural shots) work better with a
rectilinear lens.

>Alternately,
>is there a program/plugin that could correct this distortion?

You could, in theory, transform your rectilinear-projection wide-angle scene
into a fisheye-projection wide-angle scene, but something has to give - you
can't keep both the area and the angles on a flat surface.

The only way to get both is to project your print onto the surface of a
sphere.
Anonymous
April 8, 2005 7:49:13 AM

Archived from groups: rec.photo.digital (More info?)

peter wrote:
> In theory, objects that are the same size and the same distance away
from
> the lense should appear on the photo the same size, right?

Sir, the difference between theory and real world is greater in real
world than in theory, Sir.


> Are there wide angle lenses that does not have this distortion?

There are some primes that can greatly reduce that distorsion. They're
(of course) a bit expensive.
Some wide zooms can have low distorsion, but NOT null distorsion all
across the zoom range. They're (of course) more expensive than
equivalent primes.
For both, see serious reviews.


> Alternately,
> is there a program/plugin that could correct this distortion?

The epaperpress PTLens PS-plugin (I've heard that there is also a
standalone version) of Panorama Tools is (imho) great and (objectively)
free.
Btw, the other parts of the Panorama Tools may suit your assembling
needs.

Greetings from France,
Nicolas
Anonymous
April 8, 2005 3:29:23 PM

Archived from groups: rec.photo.digital (More info?)

In article <1112957353.894465.322670@l41g2000cwc.googlegroups.com>,
<nikojorj_jaimepaslapub@yahoo.Fr> wrote:
>
>peter wrote:
>
>> Are there wide angle lenses that does not have this distortion?
>
>There are some primes that can greatly reduce that distorsion.

I think you may be confusing area distortion with barrel distortion. There
*are* indeed primes that reduce area distortion - they're called "fisheye
lenses", but I rather suspect that's not what you had in mind.

>They're (of course) a bit expensive.

Fisheyes tend to be cheaper than rectilinear lenses of similar focal
lengths.

>Some wide zooms can have low distorsion,

I'm not aware of any fisheye zooms. The distortion of area is a direct
consequence of using a rectilinear projection - you can't reduce it without
distorting something else instead. These are the fundemental geometric
consequences of trying to project a spherical image onto a flat surface.

It's why Greenland and Canada look much bigger than they are on many maps.
April 9, 2005 8:49:07 PM

Archived from groups: rec.photo.digital (More info?)

Interesting idea -- use a fisheye and then convert the result to a
rectilinear photo.

How would the focal length of the fisheye lense affect the resulting photo?
Since all fisheye gives you 180 degree view, it would seem that longer focal
length (e.g. 15mm for 35mm camera) would give the best result -- as in
farther objects don't appear too small, right?

Do you know where I can find sample photos using this method? Thanks.

-peter

"Chris Brown" <cpbrown@ntlworld.no_uce_please.com> wrote in message
news:7neii2-50s.ln1@narcissus.dyndns.org...
>
>>The solution (apart special hardware with rotating lens such as Noblex
>>or Horizon chemical cameras, anyone knowing of digital equivalent to
>>these???) could be taking ONE image with a fisheye.
>>You could then (maybe, according to your taste!) rectifying it to a
>>cylindric projection, instead of the spherical projection of the
>>fisheye (please correct me if I'm wrong!), probably at the expense of
>>some loss of resolution.
>
> Yes, that's my favoured source of input for my own panoramas, but you
> absolutely have to have software that resamples.
April 12, 2005 10:39:05 AM

Archived from groups: rec.photo.digital (More info?)

On Thu, 07 Apr 2005 18:05:08 GMT
In message <oDe5e.3363$ox3.2082@trnddc03>
"peter" <nospam@nospam.com> wrote:

> In theory, objects that are the same size and the same distance away from
> the lense should appear on the photo the same size, right?
> ,,,

I've come to HATE barrel distortion. One would think that in the 21st
century these smallish dSLR lenses could be rectilinear...

Jeff
!