I'm glad this has stirred some interest.
First, I need to clarify a few things...
I'm not doing normal "panoramas", which are horizontally oriented shots,
stitched together on the sides, for a very wide perspective. Rather, what
I'm doing is stitching shots that are in the portrait orientation.
This might be the best way to explain it... the Canon 1DsII (and all Canon
DSLRs) produce images in a 3x2 format (3 pixels wide, for every 2 pixels
high). If I stitched two side by side shots in horizontal (landscape) mode,
I would end up with a 6x2 image. That's what people normally think of when
they hear stitched pano shots. But I'm putting the body in portrait
position, so each shot is 2x3. Then when I stitch two side by side of
those, I get a 4x3 format image.
So it's not really a "pano" shot, rather it's an ultra-high resolution,
normal perspective shot. Stitching this way with a 24mm shift gives me
close to the same field-of-view (and general look) as an 18mm lens, but
obviously with much higher resolution, since it's been composed of multiple
16MP images.
The next important point is parallax error, which is a major problem when
doing critical stitching of multiple shots.
Sticking a normal lens on a pano head, and rotating it around, and then
stitching the shots together - well that might all be fine for casual work.
But for highly critical work, it has some major flaws. First is the nodal
point, which you have already pointed out. But even if you nail the nodal
point perfectly, you'll have other parallax issues, because when you
"rotate" the lens on a pano head, the multiple frames you capture do not all
have the film plane (or sensor in my case) in the same parallel plane. The
camera is at a different angle for each of the shots.
You will inevitably suffer some serious degradation when doing it that way.
It gets much worse if you have both close foreground elements, as well as
sweeping background elements in the scene (and most good landscape shots
do!), as the parallax errors will be exaggerated for the foreground objects.
You'll see major ghosting, and duplicate lines.
There is only one way to avoid parallax errors...
You need to keep the lens fixed. It needs to remain in one position during
all the shots. It can't be rotated, slide to the side, etc. Any movement
of the lens will produce parallax errors.
So how do you do this? Shift lenses, combined with digital stitching tools
have opened up a new possibility and approach for this type of photography.
What you need is a lens that produces a large image circle - larger than the
sensor (or film) in your body. You can then "move" the sensor/film around
inside that image circle, and capture multiple images within the circle, and
then stitch them together for a perfect seemless stitched image with no
errors.
Here's the technique using a Shift lens with 10mm of shift in each
direction...
- Put an L-bracket on your camera body, and make small marks on the bracket
10mm apart from each other. You will need at least 3 of these marks, spaced
10mm apart.
- Mount the camera in the bracket, in the portrait position, onto a good
solid tripod, and make sure the camera is level (use a bubble level)
- meter, and set exposure in manual mode (all shots must be at the same
exposure)
- shift the lens to the left (which is actually toward the top of the
camera, since the camera is in portrait mode), and capture the first image
- shift the lens back the middle position
- NOW - slide the bracket inside your tripod clamp over 10mm to the next
mark to the left. This will perfectly compensate for the 10mm shift to the
right you just did on the lens. The lens has now NOT MOVED!!!
- Take your 2nd image
- shift the lens 10mm over to the right edge
- slide the camera bracket 10mm to the left in the tripod clamp (again, now
the lens has NOT MOVED)
- take the final (3rd) image
When you load these images into photoshop (or some other stitching tool),
you'll see roughly a 1/3 overlap between each. You combine them together to
get roughly the equivalent of 2 side by side images. When you line them up,
you will see that the seem is perfect. You can examine it at 100% pixel
view, and you won't be able to detect the seem.
If you can see any seem, then you've done something wrong in one of the
steps above, or you did not use the same exposure in all shots. Or possibly
you're using a lens that has too much vignetting, so you can see a shift in
brightness at the seems.
Lastly, as to why I don't just use a Canon 24-TSE, the answer is because it
sucks. It gets very soft at the edges when shifted. The 16MP sensor has
revealed it to be a poor performing lens under critical circumstances.
I hope that helps explain how/why I'm planning to use the Zuiko 24mm shift.
Mike
-----Original Message-----
From: olympus-owner@xxxxxxxxxx [mailto:olympus-owner@xxxxxxxxxx] On Behalf
Of Piers Hemy
Sent: Friday, April 15, 2005 5:33 AM
To: olympus@xxxxxxxxxx
Subject: [OM] Re: Lanscape's via PC stitching, was: Zuiko 18mm and 21mm
I think what you say is correct, Chuck, but needs a small elaboration.
Stitching two images from the same viewpoint using a shift lens should
provide a seamless join. If not using a shift lens, you could indeed get
the same result in the way you describe, but the seamless joint would
require the rotation to be precisely around the optical centre of the lens
in use. The centre can be found empirically with little problem, but
repeatability of the process in the field is not something I would want to
have to do.
--
Piers
PS, Walt, if you are still here, I disown the apostrophe in the Subject
line.
-----Original Message-----
From: olympus-owner@xxxxxxxxxx [mailto:olympus-owner@xxxxxxxxxx] On Behalf
Of Chuck Norcutt
Sent: 15 April 2005 12:54
To: Olympus mail list
Subject: [OM] Lanscape's via PC stitching, was: Zuiko 18mm and 21mm
--snip
If you're doing a landscape, however, I would think that this level of
sophistication could be dispensed with. In other words, creating a good
panorama should be possible with no special effort other than rotating a
leveled camera.
Since the image circle of the 24mm shift is about equal to an 18mm lens,
after shifting and combining images you should have a panorama with a 100
degree angle of view. You could achieve the same angular coverage result
with two exposures from a 35mm lens overlapped about 1/3 of their coverage.
--snip
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