There are two problems with segmented panoramic pictures. One is the
parallax problem you are talking about. If the lens is not rotated
around the entrance pupil forground and background objects will move at
different rates as the camera is rotated. There are various ways to find
the correct axis. A ground glass is probably the easiest. The finder
lend and taking lens in a Rollei are not usually the same kind of lens
but the entrance pupils are not much different so the finder will show
if the rotation is correct.
The other problem has to do with the geometry of the image. Most
lenses are designed to be rectilinear, that is, straight lines in the
original object are projected as straight lines in the image. This
results in the familiar "wide angle distortion" where objects at the
periphery of the image appear to be stetched. If the image is viewed
from the correct distance (with one eye) the distortion disappears
because the perspective effect exactly corrects the image geometry. Wide
angle distortion appears because the usual viewing arrangement is too
far away from the image. When splicing images in a panoramic group it
will be found the angles of objects at the overlap do not match unless
some method is used to correct the "distortion". Digital imaging
programs that stitch panoramic images do this and a good match can be
had. In normal darkroom work some method of curving the paper and
negative must be used to correct this problem. I am, BTW, very
suspicious of the excellent panoramic images in the old Rollei
instruction books. They are too good and make me wonder if they were not
taken with a panoramic camera.
On 1/22/2017 9:24 AM, CarlosMFreaza wrote:
I'd like to clarify that the right term is _"parallax"_to indicate if the frames coincide for the subject continuity in a stitched pano . A right rotation axis produces "parallax free" images and then they will coincide to stitch the pano, a wrong rotation axis will produce frames with "parallax" and then the pano will be difficult or impossible to stitch ( it depends about the subject features and the parallax error size). I was using the term "perspective" in my previous post as synonymous but they are not it; you can have a pano stitched with parallax free frames but with perspective distortion and a significant perspective distorsion could also destroy a stitched pano ( we largely discussed these topics a long time ago, in 2003 or 2004).
Emmanuel had calculated or had the info the entrance pupil ( the parallax free rotation point) for the SL66 seven elements Planar 2,8/80 was 90mm in front of the film plane, Siu checked it was right.
BTW, this is my test about the Rollei Panorama test rotation axis:
http://dobleobjetivo.blogspot.com.ar/2007/06/rollei-panorama-head-rotation-axis-test.html
Carlos
2017-01-22 11:40 GMT-03:00 CarlosMFreaza <cmfreaza@xxxxxxxxx <mailto:cmfreaza@xxxxxxxxx>>:
Hi Emmanuel:
A beautiful and excellent panorama as I wrote
in my Flickr's comment on your image. I never forget your
explanantions and Richard K's explanations about to find the lens
entrance pupil for the camera- lens combo to establish the right
rotation axis to take the pano shots and that interesting and
intensive thread about the stitched panos we had in this group
several years ago. I also recall the test made by Siu according
your suggestions to establish the lens entrance pupil for the
Planar 2,8/80-SL66 combo and I still have my test about the
different Rollei Pano Head versions that checked that the RPH
earlier versions directly puts the camera-lens on the entrance
pupil and then on the right rotaton axis; in the other hand the
RPH last version needs to be used in conjunction with the
Rolleifix for a right rotation axis, otherwise, if used between
the tripod and the camera directly, the rotation axis is wrong and
you could use it for very distant subjects only (always talking
about the frames perspective matching).
The right rotation axis was very significant for this my last
pano, because the subject was closer than inifinity to the camera
and it was a complex subject with a lot of trees, branches and
leaves. I kept the lens focused at infinity and used f22 for a
wide DOF, I had no perspective issues to match the frames, the
combo Rolleifix-RPH( last version) and 2,8F Planar 2,8/80 worked
fine again for the rotation axis. The true problems were to match
the frames colors, contrast and brightness. Thanks for the comment.
Carlos
2017-01-22 10:36 GMT-03:00 Emmanuel BIGLER <bigler@xxxxxxxx
<mailto:bigler@xxxxxxxx>>:
Hi Carlos from good ol' Europe
Congratulations for this nice panoramic shot. I like very
much the mood of this "green eveywhere" scene.
Believe me or not, but here in certain places of Franche
Comté, namely deep humid forested valleys of small rivers
where the sun hardly ever reaches the ground, we do have
scenes very similar to yours!
Hence your example pushes me to capture in a similar manner
the mood of our hidden parts of Franche Comté ;-)
However, sometimes, hand-held panoramic shots with no special
equipment work well,
1/ when the subjet is very far away (no need to know where the
entrance pupil of the lens is located ;-)
2/ and when the brightness range of the subject in the whole
panorama is not extreme.
Here is an example, already known to our lists members. taken
with a camera similar to Carlos' camera, a Rolleiflex 3,5F Planar.
https://www.flickr.com/photos/43175600@N00/15986052470/
<https://www.flickr.com/photos/43175600@N00/15986052470/>
Technical details :
Hand-held, no tripod, no panoramic device, same exposure time
/ aperture for all frames, frame stitching and geometry
re-calculation with Hugin and Panorama tools under Linux.
I have chosen a cylindrical projection, an orthoscopic
projection would have distorted the buidings in the edges
beyond what would be reasonable.
All the best ! The Rollei TLR rules, even for panoramic shots,
in the digital age ;-)
--
Emmanuel
