Lenticular
Same interlacing, different selector. A fold chooses by turning facets away from you. A lenticular sheet lays a row of cylindrical lenses over a flat print, and each lens magnifies whichever strip sits under its focal point. Nothing is ever hidden, only unmagnified. A lenticular can therefore hold a dozen images where a fold separates two.
Print at this pitch, not the one on the box
59.9769 LPI
The sheet is sold as 60 LPI. Print at that nominal figure and the strips creep 0.12 mm across a 300 mm sheet, enough to slip a whole view after 138 mm, which is what a band of the wrong picture down one side of a bad lenticular actually is.
The sheet in section
0.423 mm pitch · 60 LPI
8 strips per lens · substrate 0.6 mm · showing view 5
The 8 strips of one interlaced run sit under each lens, and the sight line lands on exactly one of them. Substrate thickness against lens pitch decides how far apart the strips must sit, and so how many views the sheet can hold.
Two sheets, one eye
drag to move · 709 lenses · 63° arc · right sheet drifts 2.18 views
The same file, printed twice. The left sheet changes picture cleanly, one whole view at a time, its number readable edge to edge. The right one is printed at the pitch on the packaging, and from any single position shows several views at once in vertical bands. Moving does not repair it, because the error is in the print and not in the viewing.
- Viewing angle
- 63°
- Dots per strip
- 2.50
- Views this printer can hold
- 10
- Moiré risk
- high
Moiré is the second way these fail, and unlike the pitch it cannot be fixed after printing. When a strip does not land on a whole number of printer dots the rounding error repeats, beating slowly against the lens pitch. Here each strip is 2.50 dots, 0.50 away from whole.
The pitch is not the pitch
Rays from a viewer at a finite distance fan outward, so a lens at the edge of the sheet is struck at an angle while the one in the middle is struck square. For the same strip to land under every lens, the print has to be very slightly wider than the lens array:
printPitch = lensPitch · (1 + t / (n · D)) t = sheet thickness n = refractive index (~1.56) D = viewing distance
The correction is parts in ten thousand and unforgiving. As D grows it vanishes, so sheets cut for billboards are pitched almost at nominal. Anything meant to be held in the hand needs the largest correction of all.
Against the fold
- Selector
- Facets turn away · a lens magnifies
- Images
- Two, cleanly · a dozen or more
- Transition
- Continuous blend · a flick between views
- Fails by
- Ghosting between plates · pitch drift and moiré
- Made with
- Paper and a bone folder · a calibrated printer
The fold's limit is real, two images and no more, for reasons of geometry. Everything it needs is a sheet of paper and patience. The lens buys view count with a calibration problem, and that trade is the difference between the two media.