Bart,
What is the difference between entrance pupil and nodal point?
The technical difference only matters for optics designers (
https://en.wikipedia.org/wiki/Entrance_pupil and
https://en.wikipedia.org/wiki/Cardinal_point_(optics)#Nodal_points), for Panoshooters we use the Entrance Pupil or No-Parallax point (the single apparent position of the aperture when looking in the lens from the subject side). The entrance pupil can shift a bit foreward or backward with focus distance, depending on optical design. For architecture, the distance is usuall large enough to allow a single No-Parallax point setting, for interiors if can help to calibrate for a closer focus distance, typical for the size of interior.
PTGUI is very capable in solving small inaccuracies, but mathematically can only achieve zero parallax in a single plane unless the No-Parallax point was used.
Must both be used when shooting panos?
Only Entrance Pupil / No-Parallax point matters.
A lot of what I'm doing in an upcoming project will simply involve capturing buildings that would fit fine into a 24mm T/S, but which I'll want to capture with the 45mm T/S to keep the budget down.
Totally doable, with minimal additional postprocessing, and with great resolution. You can choose whether to use multiple Shifted lens shots or Unshifted tilted shots, all perspective issues can be solved by the Stitching application and, at a distance, any parallax caused by unaligned entrance pupil positions will be small. You will want to nail the alignment of the rotation axis through the entrance pupil with subjects that have a lot of depth, or occlusions like looking through gates/arches or with street furniture, or brick roads.
As I wrote above, a three-shot pan of a building I did the other day worked fine in PTGUI. That was done without having a head to correct for the nodal point - there was nothing in the near ground that would have been affected anyway.
That's key, nothing nearby, and PTGUI by default automatically corrects for the decentered/shifted optical axis. For such a single row setup there is some leeway.
Am looking at one of these in combination with one of these
But, do I need either or both for the exteriors I'll be doing?
I also use the 300N Panoramic Rotation Unit, because the indexed stops allow me to get consistent overlaps, and I now rarely skip a shot in large stitching projects by getting distracted with many shots per row. It also allows faster shooting without having to look through the viewfinder. That can help when clouds are racing by due to high wind speeds (I shoot in the opposite direction of cloud travel, to avoid repeating ghosts anyway, so sometimes left-to-right, sometimes right-to-left). The indexing click-stops make life a lot easier, and also allow to shoot with the camera close to a back wall (often the case with interiors), because there is no need to look through the viewfinder while rotating.
I do not like the 303 Panoramic Head, too heavy and the vertical support plate cannot be shifted vertically (which might be required for some cameras if you want to expand to a multirow setup). So it only allows a single row approach and weighs a lot.
Personally I invested in a more modular system based on Really Right Stuff components (
http://www.reallyrightstuff.com/RRS-pano-gear) that can be expanded over time as the requirements grow.
For a single Row setup (assuming the optical axis is aligned sideways with the vertical panning (Yaw) axis), the "Package For Shooting Single-Row Panos: Pano Elements, LR" suffices. A camera model specific L-bracket is required.
My multirow setup was assembled over time and the individual components can be reassembled into all sorts of setups (see attached). For my Fisheye lens for 360-degrees VR shots I use a shorter MPR rail with an integrated clamp instead of the longer MPR II, to keep the rail out of the lens' 180 FoV.
EDIT: I've also added the Single Row configuration, which assumes that the optical axis aligns with the center of rotation along the Yaw axis. As you can see, simple, lightweight and quite compact. And when used with a vertically shifted TS lens, the EZ leveler II allows enough adjustment to also shoot some higher buildings without the need for a Ballhead or 3-axis tripod head with a rotator on top.
Cheers,
Bart