Re: Seitz Roundshot and QTVR technique

[jook@xxxxxxxx (Jook Leung)]

>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^>

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