Panoramics about nodal point

[swmcl]

Hi,

I just went down to my local supplier of photo gear and was interested in the Manfrotto (Bogen) panographic tripod attachment 300N. What I got was a story about how to shoot panographic images that I want to question on the forum.

The sales guy was trying to tell me that I needed to pivot the camera about the nodal point of the lens. I am guessing this is the point at which all light rays converge. By this he meant, "Buy this new fangled 303 Virtual Reality and Pan head ..." (I then told him I wanted to use a 4x5 !!!

He reckoned that the images do not suffer distortion as they would when I just whack a 4x5 on top of a rotating head.

My plan was to use a detented head like the 300N and prior to shooting, just level the tripod using its bubble level. I thought it would be a simple matter of turning on the horizontal.

I don't think the Shen Hao tripod screw is in the vertical centre line of the lens ...

Any thoughts?

[Don Miller]

What are you trying to do?

Generally,with LF panoramics are made with a single sheet of film. 6x17, 4x10, or a crop. The first multiple film method I would try is making three exposures using shift.

The salesman is right about the nodal point. It's not always critical, depending upon the relationship between near and far objects.

[Jim Galli]

What are you trying to do?

Triptych's, quadtychs. I have been questioning this too. I do know the Cirkut camera does not rotate around the node. So what is the mathematics? Interesting question Steve. I've done lots of triptychs mindlessly rotating the camera around the top of the tripod with little thought to where the sweet spot might be.

[Leonard Evens]

I am in the process of trying to master just what you have in mind.

You need to rotate the head about the entrance pupil. For most lenses you encounter this will be the same as the nodal point, but it may not be. (There was a long discussion of this issue in this forum a while back, and if you want to understand the technical niceties, search for it. ) For most normal and wide angle lenses the entrance pupil is pretty close to the front of the lensboard. For lenses of telphoto design, it is going to be somewhere in front of the lens. Fortunately, the usual interfaces to Panorama Tools such as PTGUI or hugin have the capability to correct for small errors in the position of the lens. People can even use them with handheld cameras and no panormaic head.

A good place to start to learn about this all is http://wiki.panotools.org/

In practice, here is what you do. Mount the camera on your panormaic head on the tripod and level panormaic head and the camera. Adjust the position of the front of the lensboard (or where you think the entrance pupil may be) over the pivot point. Then choose some near and far points which are in line on the gg and rotate the camera. See if they remain in line. If they don't shift the position of the lens in one direction or the other until you eliminate this parallex error. You can also check by looking at the relative positions of two points, near and far, which don't line up, to see if the distance between them on the gg shifts as you rotate. If everything is sufficinetly far awaysso that there really aren't any near and far points that will appear in the final image, it is not going to be crucial in any case. There won't be any significant parallex error.

In picking the panoramic head to use, you want to be sure it has appropriate adjustments for positioning your large format camera. Most of them are designed for use with 35 mm SLRs or DSLRs and may not work well with a large format view camera. I use the Jasper Engineering Pano Head 2 (www.stereoscopy.com/jasper/panorama.html) which works well with my Toho FC-45X, at least for horizontal panormas. It might require some fiddling to use it for vertical panoramas.

I use hugin since I work under Linux. There are several tutorials available to help with using hugin or PTGUI. There is also a yahoo newsgroup where people will answer questions. In principle, using these interfaces with large format should be easier than with smaller formats, but in practice I found it harder. If you get stuck, I may be able to help you, but I am still learning myself. I include an example below. The original is 26,300 x 6292 pixels, but of course I've reduced it significantly for display here. I made it from two images, one rotated to the left about 22 degrees and the other to the right by about 24 degrees. The lens was a 75 mm lens. The main reason I went to panoramic photography is that I want to photograph facades like this which would be impossible to do in a single shot with an available wide angle large format lens. I would have been better off had I used three images and restricted myself to the detent positions on my head, each of which represents a rotation of 15 degrees.

One problem with the software is that it it is in some ways too powerful. It will also correct pincushion and barrel distortion, which is endemic for SLRs and DSLRs, but which is negligible for large format lenses. You would think that would make it easier, but I found just the opposite.

[Bob Salomon]

Take a look at the Novoflex Panorama Q Pro http://www.novoflex.com/Einzeldatenb..._Neu_E_web.pdf

[Doug Dolde]

If you have a 4x5 with enough back shift you can just shift the back right and left then stitch the two resulting images. There is no parallax this way at all.

[Daniel_Buck]

you don't NEED a panorama head setup to take panoramas. for a full 360/360 panorama, yes you would probably want a pano head, but for simple one or two row panoramas (like a 6x2 grid, or something) you don't need a panorama head. any differences in paralax aren't going to be that big, unless you are shooting something that is very close to the camera.

[Helen Bach]

Doug wrote: "If you have a 4x5 with enough back shift you can just shift the back right and left then stitch the two resulting images. There is no parallax this way at all."

...Or if you use a slide bar (Jasper Engineering makes an excellent heavy duty version) you can use front shift as well as back shift.

Swing lens cameras usually rotate the lens about the rear nodal point, not the entrance pupil, by the way. It's a different situation.

Best,
Helen

[Leonard Evens]

A couple of comments.

First, I mispoke about checking the separation on the gg of a near and far point. What should remain the same in the absence of parallax shift is the angle between the rays from the entrance pupil to the the points. But if this angle is small, and if you don't rotate too far, the horizontal distance on the gg should stay pretty much the same. In the example I posted, note the right hand side of the marquee which is almost, but not quite perpenducular to the plane of the facade. Also, look at the strut just above it. I examined both when setting up my camera to be sure I didn't have any significant parallax shift. It is best, of course, if you have a near and far point which should be in line with the entrance pupil, or at worst would be in line if they were at the same height.

Second, it is certainly true that you can avoid the whole issue just by shifting the back in both directions. But that will only allow a relatively minor extension of the angle of view. Thus, I would never have been able to encompass the whole facade in the example I posted that way.

[Walter Calahan]

Panos made simple. Go to 'Really Right Stuff' web site. They spell out exactly what you have to do, and sell excellent equipment to do it.

http://www.reallyrightstuff.com/pano/index.html