Re: [Rollei] Re: Rollei panorama head, and "nodal points"

[Carlos Manuel Freaza <cmfreaza]

Emmanuel:
          The technical discussion about "nodal
points", rotating panoramic camera, TLR standard
panoramic head,etc. is actually  very 
interesting for me, but I think that there is a point
no considered. If the image's distortion occurs in the
edges principally, the Rollei panoramic head reproduce
a portion of the previous frame during a sequence,
then, if you cut each frame in the point where both
coincide, the distortion in the edges almost
dissapears because the edge dissapears, at least I
have this impression looking my panoramic views on
paper.
In fact, the Rolleiflex TLR has a narrow body and it
rotates with the taking lens near the panorama head
axis in favor of the sequence quality. I have the last
panoramic head model and it works very well in
practical use.
All the best
Carlos
  
 --- bigler  escribió: > > > Carlos Manuel
Freaza:
> > > > About the frames a bit closer, I think it
> depends
> > > > subject and distance to subject.
> 
> > > Richard Knoppow : 
> > >...Note, that since the lens moves with regard to
> the swivel
> > point of the adaptor when the distance of focus is
> changed
> > that the match with the nodal point will not be as
> good for
> > close objects as for distant ones. 
> 
> 
> The question of identifying the best rotation point
> for panoramic
> stitching is a FAQ but the answer is not so obvious.
> Usually "nodal
> points" are invoked, but this, pardon me Richard, is
> not always true.
> And since we are in the Temple of Optics here, I
> dare to add the
> following comments.
> 
> In panoramic cameras with a rotating lens drum and
> fixed film
> w/respect to the landscape, like a Noblex, a Horizon
> or an Alpa
> rotocamera (360degs), yes, you should rotate the
> lens around its rear
> nodal (or principal) point. This for keeping the
> image almost at rest
> on film, for sharpness issues while the lens
> rotates.
> 
> But for conventional panoramic stitching like with
> the Rollei TLR or
> any conventional camera, where the whole camera is
> rotated w/respect
> to the landscape, the proper rotation point to avoid
> parallax effects
> is the __entrance pupil__. This fact is stated by
> Kingslake and some
> other old textbooks, but is almost never explained
> in detail. The
> basic reason why the pupils play a role here is that
> parallax effects
> occur between out of focus image projections. An out
> of focus image is
> built from small circles, each one being the
> projection of the exit
> pupil on film. May be there is one object plane
> exactly in focus, but
> when taking pictures of a flat object, you do not
> have to care for
> parallax effects.
> 
> Rotating lens drum panoramic cameras do not respect
> the 'no-parallax'
> condition, since the entrance pupil hardly ever
> coincides with the
> rear nodal point. A detailed analysis of this is
> fascinating but would
> be far off-topic here, but it suffices to say that
> those panoramic
> cameras usually have a wide-angle lens, and that
> they are equivalent
> to stitching many vertical strips of very narrow
> width, hence parallax
> effects are small. Out of focus image points are
> slightly stretched
> under the form of an oval shape, so conventional
> parallax effects for
> out of focus images are somewhat blurred in an
> unconventional manner.
> 
> So the proper rotation point for panoramic stitching
> is the entrance
> pupil. In quasi-symmetric lenses like a R-TLR lens,
> the entrance pupil
> is located very close to the front nodal point of
> the lens. Another
> source of confusion with nodal points !! So in order
> to minimise
> parallax effects with a R-TLR, simply try to place
> the rotation point
> roughly under the lens. A Rolleifix will do that
> pretty well. My
> understanding is that some, but not all, R-TLR
> panoramic attachments
> move the screw under the lens near the entrance
> pupil.
> 
> No what happens with non-symmetric lenses, like
> retrofocus wide angle
> lenses or telephotos. 
> 
> For such lenses the entrance pupil is _not_ located
> at the front nodal
> point, nor at the rear nodal point. Basically this
> depends on the
> degree of asymmetry of the design, more precisely
> and very simply in
> terms of mathematics, it is given by the amount of
> pupillar
> magnification of the lens design. This is tabulated
> in manufacturers'
> data sheet (I mean : good manufacturers, obviously
> the only ones where
> RUGgers buy their lenses ;-);-);-). In German
> datasheet, the acronym
> EP for "Eintrittspupille" is used, AP for
> "Austrittsspupille". EP is a
> fairly obvious acronym for English-speaking readers.
> EP is often
> measured with respect to the front lens vertex.
> datasheet usually
> mention the diamter of the pupils, so it is easy to
> compute M_P and
> check what follows.
> 
> Let M_p be the pupillar magnification factor equal
> to the ratio of
> (exit pupil diameter / entrance pupil diameter), the
> distance between
> the front nodal point H and the entrance pupil E_p
> is given by : 
> 
> HE_p = f*(M_p - 1) / M_p.
> 
> where f is the focal length. When M_p = 1, the
> entrance pupil is equal
> to the front nodal point. This applies to all true
> symmetrical lens
> designs such as classical apo-chromatic process
> lenses (apo-ronar,
> G-claron). Most view camera lenses are
> quasi-symmetric, hence the
> entrance pupil will be located somewhere in the
> front half of the
> glass, close to the front nodal point.
> 
> For a retrofocus lens like Zeiss Distagons, we have
> M_P > 1. For such
> a retrofocus, the entrance pupil will be located
> ahead from the front
> nodal point, probably in the air in front of the
> lens. For a
> telephoto, we often have M_p < 1. Here the entrance
> pupil will be
> located behind the front nodal point. Since the
> front nodal point is
> in fact behind the rear nodal point (H and H4 are
> crossed in a
> telephoto design); it happens that the entrance
> pupil for telephoto is
> located in the film plane !! this is actually
> something very hard to
> figure out ; however the consequence of this is that
> you do not have
> to add a long rail in order to properly set the
> right rotation point
> for panoramic stitching with a telephoto ! for a 35
> mm camera, the
> tripod screw is close to the film plane and a small
> adjustment on the
> slot of your tripod head will do the job !!
> 
> However aficionados of astronomical telescopes or
> "Telyt"
> non-telephoto design of long focal lengths (without
> the usual negative
> rear element of a telephoto), they'll have to rotate
> their camera
> under the front part of the lens (usually a cemented
> doublet or
> triplet), just under the glass like if it were a
> single lens element.
> For, say, a 300 mm non-telephoto lens or a 300mm
> process lens used as
> a long focal lens on a view camera, no way but
> rotating at 300mm ahead
> from the film plane. Not a problem with a monorail
> view camera, but
> this requires to use an accessory rail on a 35mm
> SLR.
> 
> -- 
> Emmanuel BIGLER         
> <bigler   

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