My query is really somewhat more complicated than contained in this thread's subject wording. I've read a fair share of the instructions for calculating no-parallax points for fixed focal-length lenses, and in fact have successfully done so for my panoramic photography efforts with those lenses.
Hi Jim,
I'm not sure which calculations you are referring to, unless you only use symmetrical lens designs. Several modern lenses also use internal focusing mechanisms, so the no-parallax-point (NPP) can potentially shift a bit with a change of focus distance.
However, I have begun to use zoom lenses, with variable focal-length settings, for taking panoramic photos. This is probably an impossible query, but does anyone have a ready (i.e., simple and quick) method for such calculations when in the field attempting a panoramic photograph after the framing is decided upon on the spot with a zoom lens setting?
Again, calculations can be wrong. The only way to do it well for an actual lens/focus distance is by testing for parallax when the camera rotates from side to side with the assumed entrance pupil as rotation point/axis. For that you need a closer and a more distant feature that overlap, and monitor if their relative position shifts when you rotate the camera. Live View can be very helpful if you can't inspect the images on a larger screen in the field.
With zoom lenses the whole optical design changes as you zoom, so I would also suggest to determine the NPP at a few fixed zoom positions, and interpolate for intermediate positions. When you use a good blending program, then minor inaccuracies will be hidden, although when closeup control points are used then lens-distortions will by misinterpreted and the overall stitching could become problematic. It always helps to get as little parallax as possible, but when in doubt just avoid close-up control points during stitching optimization.
Cheers,
Bart
