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[OM] Re: Lanscape's via PC stitching,

Subject: [OM] Re: Lanscape's via PC stitching,
From: "John A. Lind" <jalind@xxxxxxxxxxxxx>
Date: Sat, 16 Apr 2005 20:05:45 -0500
At 05:13 PM 4/16/2005, Tom Scales wrote:

>All excellent points and for some of these locations, I will likely redo the
>shot on a tripod. Many are on a bike trail and we ride our tandem in and
>carrying more than just a camera can be a challenge (any bicyclists with
>recommendations on a good way to carry a heavy camera and have it ready to

I realize there are times when it's simply not possible to do a thorough 
setup, and that's the additional benefit of software such as PhotoVista 
(and the "free" AutoStitch posted here).  PhotoVista can do a decent job of 
compensating and adjusting things in adjacent photographs that don't fit 
together well . . . within some limits though.

The primary thing gained by aligning rear lens node over the tripod's 
rotational axis is eliminating parallax shifts in the overlapping regions 
of the images.  Indeed, the "field" method of alignment creates conditions 
that produce dramatic parallax shift and adjustment is made until it's no 
longer detectable.  The method I use is placement of a thin vertical object 
very close to the camera with a very distant background that also has 
strong vertical lines, or at least something against which the close object 
can be seen to shift easily.  The camera is then set with the near object 
in view at the left edge of frame and rotated until it's at the right edge 
of frame.  Fore/aft adjustment of the camera is made until the background 
no longer appears to shift behind the very close object.  (Left/right 
adjustment is fairly simple with most cameras . . . to center the lens axis 
over rotational axis.)

When PhotoVista (or other stitching software) encounters parallax shift in 
an overlapping region, it attempts to use the parallax of one or the other 
and will "blend" things between the two in mismatching regions to hide 
it.  PhotoVista does this rather well, but can have problems with hiding or 
blending it completely if the parallax shift is between very prominent or 
very high contrast objects.  The same problem occurs if people or things 
move around in successive photographs in areas that overlap with adjacent 
photographs.  Sometimes it can hide this fairly well; other times it's 
still detectable in the output photograph.

The other software posted, AutoStitch, looks as if it is specifically 
geared to assembling mosaics . . . and based on what I saw in the examples, 
it appears its authors made presumptions that overlapping regions might 
have some hideous mismatches.  I've downloaded it and will eventually play 
with it using some of my less than well executed sets of pano photos.  I've 
managed to "kick the tripod" or do something else a few times without 
realizing it and ended up with a shift in rotational axis in the middle of 
the shots.

BTW, the lens you used doesn't appear to have too much Cos^4 falloff . . . 
a problem I encountered the first trek out . . . using a 28/3.5 SC (which 
is noted for its falloff).  The same lens also produced some hideous 
aperture flare!  I learned from that experience that shading the lens front 
from the sun is crucial, unless the sun is actually in the field of view.

Keep shooting 'em and have fun with it.  When you get a good one, it looks 
"way cool."

-- John

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