Stitching — where it appears
Named by 7 essays across 2 fields — each of them below, with the objects they name alongside it.
Focusing moves the pivot past its best place
Focusing a fifty-millimetre lens to one metre carries its entrance pupil 2.63 millimetres forward of the camera body, and to half a metre 5.56 — which is more than the whole 5.53 that the pupil walks with field angle, so past a subject at 502 millimetres the focus decides where the pupil is. A panorama head aligned at infinity and used at a metre leaves 7.46 arcminutes along its seam; aligned at four metres it leaves 2.21, better than pivoting at the pupil at all.
The pivot that is not the eye
A camera bolted to a tripod turns about the screw under its baseplate, and the light crosses somewhere else. Every ray of the panorama that results passes the pivot by e sin γ — the offset times the sine of how far off its own frame's axis the ray points — so the picture has a radius where a projection would have a point.
The parallax you cannot shoot away
A stitched panorama's parallax has two halves and they do not behave alike. The one across the seam falls as the sine of half a frame spacing, so more frames buy it off; the one up the frame is the sine of half the frame's own height, and no quantity of shooting touches it. They cross at π over β, which has no pivot error in it at all.
A rig is right on one surface
Several cameras looking outward have several centres, and no warp registers all of a scene. The residual is a disparity, so the depth the stitch is computed for has an exact optimum — the harmonic midpoint of the depth range, not the middle of it — and the arithmetic middle costs a factor of 2 z_far over the sum, which tends to two.
A refocused panorama is six lenses
Refocus between the frames of a room panorama and each frame is its own camera: its pupil carried forward by its own extension, its picture made at its own principal distance. The best fixed pivot then leaves 12.9 arcminutes along the worst seam, and a head that slides the camera back as the lens extends leaves 2.82 — the lens's walk alone. The pivot's share is first order and worth a tracking head indoors. But a stitcher that reads all six frames with one focal length misregisters by up to 270 arcminutes, which is the larger mistake by ninety times.
One focus stopped down is as sharp as six in a deep room
Refocusing a room panorama frame by frame costs a seam of 12.9 arcminutes on a fixed head. One focus stopped down costs none of that, and at f/40 holds half a metre to four metres to 5.27 arcminutes — sharper than the fixed head's seam, blunter than a tracking head's 2.82. But the comparison flatters refocusing: the frame on the table also holds the wall behind it, so it cannot be held sharper than 5.27 however it is focused. Counted properly, one focus on a plain head comes within 2.4 per cent of the geared one, and pays for it in light.
The hole a rig cannot fill
A two-lens spherical rig covers every direction between its two lenses and still cannot see 0.470 per cent of the sphere directly beneath it, reaching 12.8 degrees from straight down — its own tripod, standing exactly where neither lens can look. No arrangement of lenses removes it, because it is not a gap in coverage; it is the rig occluding itself.
Named alongside it
The objects these essays reach for when they reach for this one.
PanoramaParallaxcentre of projectionEntrance pupilinstrument limitDemonstrationPicture surfaceThin lensFocal lengthBaselineCausticChief ray