Newsgroups: rec.photo

In rec.photo, tjl@cbnews.cb.att.com (timothy.j.lipetz) writes:



>  There was some discussion recently about rectilinear
>  fisheye lenses.  Could someone please give more
>  explanation of how pictures made with them would look?

>  I have considered getting the Mamiya 24mm lens for my
>  645S.  Mostly, what I would like to do is use the center
>  horizontal portion of the negative for panorama shots.
>  Maybe use a 24 x 56 mm section, which is what a
>  Widelux negative would be.  Used this way both the
>  Mamiya and Widelux would cover about 140 degrees
>  horizontally.  How would the two images compare?

...

>                             However, the subjects were
>  desert rocks, etc. and I wonder if the fish-eye effect
>  might be less acceptable if the subject were buildings
>  and streets.  Is this a correct concern?  Would straight
>  vertical lines be noticably bowed out from the center?
>  (Of course, I know the camera must not be tilted.)

ORIGINAL SUBJECT:

          --------------------------------------------
          |                    |                     |
          |                    |                     |
          |                    |                     |
          |                    |                     |
          |                    |                     |
          --------------------------------------------

WIDELUX PHOTO:

                     ----------------------
          -----------          |           ----------  (<- gently curving
          |                    |                     |  "horizontal" lines
          |                    |                     |   damn ASCII)
          |                    |                     | (<- Straight verticals)
          -----------          |           ----------
                     ----------------------

FISHEYE PHOTO:
                            
                     ----------------------
             --------          |           ---------   (<- gently curving
           /                   |                     \  "horizontal" lines
          |                    |                     |   damn ASCII)
           \                   |                     / (<- Curved verticals)
             --------          |           --------- 
                     ----------------------

In general:

Fisheyes curves all straight lines that do not pass through the center
of the frame. A vertical line is no different than a diagonal or a
horizontal to a fisheye lens.

Widelux (or other curved film cameras) curve all straight lines that
A) are not vertical and B) do not pass through frame center. Vertical
lines are "sacred" to a Widelux camera, as the lens is a regular recti-
linear (no linear distortion) design, and the film is flat in the vertical
dimension, just like a standard camera. In the horizontal plane, the
Widelux looks sideways at the subject when it is imaging at the sides of
the frame. Parallel lines must converge, just as they do when you look
down a set or railroad tracks.

What I think is extremely interesting about the unique perspective of a
Widelux is that you are unrolling a curved view and flattening it. If you
took a shot from the inside of a circular room (like the Capitol Rotunda)
at the center of the room, the resulting photo would look like you had
unrolled the circular room and turned it into a perfectly rectangular one.
If you had used a fisheye from the same spot, the sides would still be
rounded and bowed and the illusion would fail.

For natural subjects where there may be no linear points of reference,
it can be quite difficult to tell if there even is any strange perspective.
A fisheye by contrast almost always calls attention to itself.

Another strangeness which can be good or bad is the sequential nature of
the exposure, especially at slow shutter speeds. It can take a few seconds
to complete the scan as the lens turns. A fisheye on a regular camera of
course is simultaneously exposing the whole frame.

The downside of a panoramic camera is that they are usually quite limited
in adjustments such as shutter speeds and focusing, so there are some
situations in which they are very difficult to use. In those cases a fisheye
on an SLR can get the job done, even if differently.

BTW, you can tilt a Widelux, if you don't mind the horizon getting
curved. It can mimic a fisheye in that case. In some natural settings
that curvature can straighten out a natural curve, like the cusp of a
sand dune. Explore!

Tony Arnerich
tonya@hpldsla.sid.hp.com