FW: Seitz Roundshot and QTVR technique

[Mike Sinclair <sinclair@xxxxxxxxxxxxx>]

Joshua eludes to the beauty of pan-scanning an image with a 1D sensor - with
either a 'slit' of film or a linear CCD. During my 2 yr. ownership of a
Roundshot, I religiously adjusted the nodal point adjustment rails to what
the computer told me. After a few weeks and getting lazy, I ignored the
adjustment and saw no difference in the images. This, in part was because of
the slit and part because I used a 14mm lens. I'd imagine if you were using
a significantly longer fl lens, objects violating the nodal point
calculation would appear horizontally blurred - their image components would
have a non-zero velocity with respect to the film.


As a side note:

A digital video camera's video can be processed to yield a true 720 x 2880
(lens dependent) x 360 panorama. VideoBrush's technique is more akin to the
pan'n'snap variety and produces inferior results (IMHO). If you violate the
nodal point rule (on purpose) that the pan'n'snap photographers are slave
to, you can get  truly stunning stereo panorama pairs - with only one camera
and one pass! Through computer processing, you can derive stereo pairs with
as much as a 12" (or more) IPD (distance between viewpoints). I'm hoping the
lab in which I used to work will soon make available or license this
software. It makes web-resolution panos VERY easy to make - much easier than
the snap'n'pan variety. Also, through multiple pans, pole-to-pole coverage
(360 x 180 degrees) is attainable. Another advantage of this technique is
the auto exposure capability as a function of pan angle (similar to what the
new RoundShots give you). This comes with every DV camera! I've seen image
compressions of 7+ stops while panning an interior next to a window with a
bright sunlit exterior view - both with good exposure. Almost all of the
pan'n'snap real estate pans suffer from "window burnout". Another advantage
is that you get about 60 pans per $20 digital tape - hard to beat compared
to FlashRam or film.

-Mike-



> -----Original Message-----
> From:	jook@xxxxxxxx [SMTP:jook@xxxxxxxx]
> Sent:	Thursday, November 05, 1998 3:41 PM
> To:	panorama-l@xxxxxxxxxxxxxxxxx
> Subject:	Re: Seitz Roundshot and QTVR technique
> 
> >Jook Leung wrote:
> >
> >> Do users set their lens focus at infinity and put that value into the
> >> RoundShot or can I apply closer focus setting and use hyperfocus-depth
> of
> >> field/f-stop settings to keep infinity also in focus?
> >
> >I don't have much experience with the RoundShot, but I use the Sigma 14
> on
> >my digital pano cameras.  When used full open at f/2.8, I need to set the
> >focus to 0.7 or 0.5m to have most near and far objects in focus.
> >
> >
> >> The term "Nodal point" is only mentioned once in the manual and is not
> >> normally accounted for as it is
> >> in other QTVR rigs. So that was absolutely confusing.
> >
> >Don't worry about the nodal point in a slit-scan camera.  It is a problem
> >for QTVR rigs because when stitching you need to match up the left side
> of
> >one shot with the right side of the next shot.  If the shots were not
> taken
> >from the nodal point, the effective point-of-view will have changed as
> the
> >camera rotated.  If a slit-scan camera rotates from other than the nodal
> >point, the change in viewpoint is gradual.  And, since the film is only
> >recording the portion of the scene looking straight ahead, the effect is
> all
> >but unnoticeable.
> >
> >> Yikes, horizontal bands of flare at bottom of image: Taping a curved
> piece
> >> of black paper over the backside of the compendium will take care of
> the
> >> flare problems of the Sigma 14mm lens.
> >
> >I get those bands too.  Can you say more about how you do this masking?
> >What is the backside of the compendium?
> >
> >
> >=Josh
> >++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  Joshua D. Eskin, Ph.D.  Panoptic Vision, Inc.,  Boulder, CO
> >  Voice: 303-417-9800   Fax: 303-440-6162      www.pancam.com
> >++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 
> Thanks Joshua for the clear explanation of why the nodal point does not
> matter for
> slit cameras.
> 
> Flare gets into the Sigma 14 from the corners of the fixed lens shade that
> are cut out to allow
> the lens to see its full coverage. When the lens is used in its 90 degrees
> portrait orientation for QTVR
> and at 45 degrees on the Roundshot, lights from above and the corners will
> hit the front element
> of the lens causing problems with flare.
> 
> On a PeaceRiver rig I used a vertical L-bracket arm that has metal leaf
> from a discarded barndoor
> on a small ballhead that I can swivel around until the flare is
> eliminated.
> Sometimes I'll also
> drap a small black piece of cloth over the barndoor to box off the lens
> when there are lots of overhead lights.
> 
> The Roundshot lens compendium is like a vertical lens cap with a slit tall
> enough to allow the widest
> lens to see its vfov. With the Sigma's shade cutouts facing up, light from
> above and behind will still
> hits the front element.
> 
> I took a piece of black paper about 6x10 inches, with tape along one side,
> held the paper shade off the
> back side of the compendium like a curved awning, keeping the paper away
> fom the slit where the lens needs to see thru.
> 
> 
> <^J^>
> 
> ---------------------------------------------------------------
> JOOK LEUNG    jook@xxxxxxxxx    http://360vr.com    201.894.5881
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