Can someone please explain this "nodal" stuff to me? As I understand it, the ideal panorama is taken by rotating the camera and lens about the lens's nodal point. But, why? Does it make any real difference or is it just one of those theoretical issues that some (unnamed) people love to fuss over?
Hi Peter,
It's to avoid parallax (shifted images) in either foreground or background. When foreground and/or background do not perfectly overlap at the transition between the images, it can become difficult to smoothly blend the images into a single image, especially when you have only a small overlapping zone between images.
Try looking at a distant point, an hold your arm stretched in front of you, stick your thumb up. Now look at it with one eye closed, and then switch to the other eye closed. You'll see your thumb jump left and right in front of an otherwise stationary background. It would be impossible to blend those two "images" into a single wider one, without laborious masking.
The larger the difference between foreground and background features, the smaller the distance between the two entrance pupils of the lenses must be to avoid potential issues. When the two NPPs are aligned, and you rotate through that point, there will be no parallax and alignment in the overlap zone can be made perfect (by also allowing to eliminate lens distortion).
FWIW, I recently returned from a trip to southern Utah and Colorado where I took quite a few panos using a D600 and Nikkor 70-200mm f/4 (and a few with the Sigma 35mm f/1.4) The "nodal point" was my feet and I just turned and clicked, making sure to overlap the images by a good bit, using aperture priority. I have been processing with PTGui and have some wonderful results. How would the nodal point make my panos better?
Your foreground features were either far enough away or with too few predictable patterns that PTGUI could not use its clever/smart blending to hide the double or differently angled features. Try shooting something with more foreground detail, and you'll soon find out things can become impossible to hide, especially when you only have a small overlap zone. That sucks if you cannot redo the shot.
Cheers,
Bart