Halve the layer height and the exposure does not halve

A resin file says 2.5 s at 0.05 mm. Cut at 0.03 mm and Encrust writes 2.05 s, not the 1.5 s that proportion gives. Cut at 0.1 mm it writes 4.12 s, not 5. Those are the figures for the app’s “Generic resin” (2.5 s normal, 30 s bottom), computed from the formula below. They are not a measurement on any printer or resin.

The curve

Cure depth follows the working curve, the standard cure-depth model of resin printing, usually credited to Jacobs. We cite no paper for it, only our implementation. The dose a layer needs is its inverse:

Cd = Dp * ln(E / Ec)        E(L) = Ec * exp(L / Dp)

In a resin file the terms map like this.

Term	Meaning	Where it is in the file
L	layer thickness, mm	layer_height_mm (the height the exposure was measured at)
E(L)	dose a layer of thickness L needs	exposure_s, in seconds, at that height
Dp	light penetration depth, mm	penetration_depth_mm, optional
Ec	critical dose, below which resin does not gel	not stored: it cancels

Encrust never needs Ec. It carries a resin’s exposure from the height it was measured at to another by the ratio, which is all that exposure_for_mm (source) computes. The profiles design note states the rule:

E_new = E_measured * exp((L_new - L_measured) / Dp)

Exposure rises by a factor of e for every Dp of extra thickness. It does not fall to zero at zero thickness, which is why a thin layer takes more than its share.

The numbers for 0.05 to 0.03 mm

The factor depends only on the height change and Dp. With the assumed Dp of 0.10 mm, computed from the formula, not measured:

From	To	Share of exposure kept	Generic 2.5 s becomes
0.05 mm	0.03 mm	82%	2.05 s
0.05 mm	0.025 mm	78%	1.95 s
0.10 mm	0.05 mm	61%	1.52 s (if the 2.5 s were set at 0.10 mm)
0.05 mm	0.10 mm	x1.65	4.12 s

The carrying is also consistent: going 0.05 to 0.08 to 0.03 gives the same figure as going straight, because the exponents add. A test in the source checks that.

How wrong the assumed depth can be

The factor for 0.05 to 0.03 mm at three depths, computed from the same formula:

Dp	0.05 to 0.03 mm	0.05 to 0.10 mm
0.05 mm	67%	x2.72
0.10 mm (assumed)	82%	x1.65
0.15 mm	88%	x1.40

The 0.05 and 0.15 mm rows are what-ifs, not resins we measured. They show the spread: if your resin’s real depth is 0.05 mm, the assumed value writes 82% where the curve gives 67%, and for 0.05 to 0.10 mm it writes x1.65 where the curve gives x2.72, about 40% less exposure than that curve calls for. The gap widens with the distance from the height the resin was measured at.

Why the bottom block is exempt

Bottom layers are exposed long to bond to the plate, not to cure through a given thickness. Encrust leaves the bottom exposure as it is when the layer height changes (profiles design note). Going from 0.05 to 0.1 mm raises the generic resin’s normal exposure from 2.5 s to 4.12 s and leaves its 30 s bottom exposure at 30 s. The transition layers ramp between the two, so they move with the normal value.

What to do

Treat the carried number as a starting point for one printer and one resin. Your resin maker’s exposure for your printer at your layer height comes first. If the maker gives none for 0.03 mm, start from the carried value and print a calibration piece before a real part.

The panel, its “Carried from” label and the button that restores the old value are covered step by step in Exposure, lift and rest times. The files that hold a resin’s numbers are in Printer, resin and support profiles.

If you have measured a resin’s penetration depth, set penetration_depth_mm in its resin file and the carrying uses that instead of 0.10 mm.