Inside the tube

A night vision goggle is a chain. The objective lens gathers what light there is onto a photocathode, which turns it into electrons. A microchannel plate multiplies those electrons thousands of times over. They strike a phosphor screen, which glows, and the eyepiece shows you that glow. Everything you see through a goggle, the grain, the halos, the green, comes from one link or another. The plugin draws each of them, in order, from the light your scene renders.

The light it amplifies#

A tube can only amplify light that's there. Starlight, a sliver of moon, the glow of a town over the horizon: a tube gathers it all and turns it up, while the eye beside it sees almost nothing.

The goggle reads your scene's light as it goes by on its way to the tonemapper, before the game's exposure has brightened it, and amplifies that. So a dark yard reads as dark to the goggle even when the camera's auto exposure has lifted it, its darkest corners keep what light they have, and a floodlit gate is far brighter than the moonlit field in front of it, as it really is.

Gain#

Gain is how far the tubes amplify the light at most, in the darkest scene: more reaches further into the dark and brings up more grain with it. With Auto-Gain on, the tubes turn their gain down as the light rises, to hold the picture's brightness at the Auto-Gain Level, as a real tube's automatic brightness control does, down to its Lowest Gain. Turned off, the player sets the gain, a knob's turn at a time, with Gain Up, Gain Down and Set Night Vision Gain.

Auto-gating#

A modern tube copes with a sudden bright light by gating: it switches the voltage on its photocathode on and off thousands of times a second, spending less of each instant switched on as the light grows. It reacts so fast that a muzzle flash or a headlight swinging round dims the picture rather than blinding it.

The goggle settles on a change in the light over Auto-Gate Speed, in seconds, turning down for a brighter light twice as fast as it turns back up for a darker one. Auto-Gate Sensitivity is how fully it answers: at 1 the picture holds its level whatever the light does; lower, it brightens and darkens with the scene and pumps less.

Halos and bright light#

Point a goggle at a light and it grows a halo: a bright disc round it, the size set by the gap between the photocathode and the plate, smaller on newer tubes. Halos is how strong they are and Halo Size how far they spread.

Bright Light Protection dims the tubes by how much of the view is burning out, not by one bright spot, so a lamp in a dark room counts only for the share of the view it fills, and the rest of the room stays readable round it.

Grain, honeycomb and blemishes#

In very little light a tube's picture sparkles: there are few enough photons that each one shows, and the plate adds its own noise. Grain is how much of that sparkle there is, and Grain Size how large each speck is on screen. It follows the light: a quarter more than the setting once the gain has climbed as far as it goes in the dark, about half in good light, and more again in the darkest corners of the picture. A better tube has a lower setting, so less grain in the dark: of the new tubes here, the monocular's is a good mid-range one, the binocular's better, and the panoramic's the best there is.

Among the grain, a few specks flash bright where the picture is dark: single photons striking the tube. Sparkles sets how many, 1 as designed and 0 none, and Sparkle Size how big each one is, in grains across. At 1 it's a single grain; bigger, it's a round point with a soft edge, and there are as many to the area whatever their size.

In bright light the plate shows its own structure, a faint hexagonal mesh where its fibres were fused together: Honeycomb. And every tube has a few blemishes, small dark specks fixed in the tube, the cosmetic flaws its inspection allowed. Blemish Count, Size, Darkness, Softness, Roughness and Variety set them up, and Blemish Pattern picks which ones a goggle has. They're the same every time it goes on, so give each goggle in your game a number of its own.

The phosphor#

The glow you see is the phosphor screen. Green phosphor was the first choice because the eye tells more shades of green apart than of any other colour; white phosphor shows a grey picture with a cool blue cast, which many find easier to read for contrast. The phosphor is the effect's Second Colour. Phosphor Saturation is how deep the colour goes, Highlights Pale how far the brightest parts run towards white, Black Level how dark the darkest can get, and Contrast how hard the picture is.

Phosphor keeps glowing for a moment after the light that struck it has gone, so a bright light moving across the view leaves a fading trail: Afterglow. Warm-Up Flicker is the stutter as a tube comes up to power.

The eyepiece and the goggle#

Through the eyepiece a tube's picture is a round field of about forty degrees. Where your eye sits matters: too far back and the circle shrinks; off to one side and its edge closes in. Eye Relief sets how far back the eye is, and the goggle's own movement does the rest.

Tubes is one, two or four. A single tube is worn over one eye while the other sees the dark round it: Bare Eye is how much of the world shows round the tubes. At 1 everything outside them is exactly the picture the game draws; lower, it darkens, as it does when both eyes are behind tubes. Four tubes make a panoramic, the outer pair angled out to widen the field. All four run into one view, as a binocular's two do: the inner pair fuse into one round view overlapping the outer tubes, and the world runs straight on across into them, with no line between. It's one block, so it moves as one: as it slips, the shadow of eye relief closes in on the block from its own edge, never between its tubes. Outer Tubes Out, Outer Tube Size, Seam Darkness and Seam Distortion shape it.

A goggle on a helmet mount moves against the eyes as the head turns. Moves With You and Weight set how it lags and swings, a clip-on adds its Clip-On Weight, and Movement Smoothing takes the jitter out at the cost of a little lag. 3D Housing draws the goggle round the tubes as you'd see it from inside, in Housing Shape. It's a couple of centimetres from the eye, far too close to focus on, so Housing Blur softens its outline; it softens outwards, so the housing stays solid right up to the glass.

At the rim of the field a tube bends and darkens the picture, more so on old tubes: Edge Distortion, Edge Darkening, Edge Glint and Edge Blur.

Focus#

A tube's objective is a fast lens, so its depth of field is shallow up close. Focus Distance is where it's focused, in metres, and at 0 everything is sharp. The Aperture says how much it blurs what isn't in focus: wide open, little is sharp and the most light comes in; stopped down, more is sharp but there's less light to amplify, so the picture darkens and the grain comes up. Focus Blur scales the blur and Most Blur caps it. Pinhole Cap is the cover a goggle wears to be used in daylight. The starter goggles are focused at 4 m, as for clearing rooms: the room is sharp and the weapon in your hands is soft.

Something near and well out of focus doesn't just go soft inside its own outline. Its blur spills out over whatever's behind it, the way a weapon held up in front of a goggle focused across the room looks, and Out Of Focus Spreads turns that on. A first person weapon drawn with First Person Scale sits nearer the eye in the picture than it really is, so it reads as further out of focus than it would be; if it's too soft, lower Most Blur.

The blur costs more the more of the picture is out of focus. Blur Quality trades its smoothness for its cost: Optimised looks at half as many places and leaves slight blur to the grain to hide, Default is as designed, and Quality looks at twice as many, smoother on a large blur.

Daylight and the auto shutoff#

In bright light a tube washes out to a glowing haze: Daylight Washout is how far. A real goggle protects its tube with a light sensor that switches it off if it stays bright. Auto Shutoff does that when the picture stays brighter than Shutoff Brightness for Shutoff After seconds, and Switches Back On brings it back once it's been dark again for Back On After seconds. It's a goggle's behaviour, so it works on goggles put on with Equip Night Vision.

Power is the goggle's switch. Off, the tubes go dark as their phosphor fades, and the goggle stays where it is.

Old tubes and new#

Tubes have improved in steps over the decades: brighter photocathodes, quieter plates, smaller halos, finer detail. The goggles that come with the plugin carry two of them. Old tubes are grainy and weak in the dark, with wide halos, a bent and darkened edge, glowing blacks, slow phosphor, a gain slow to settle and plenty of blemishes. New tubes have fine grain, reach much further into the dark, stay crisp to the edge, and have no blemishes. Every one of those is a setting, so anything between them is yours to tune.

The thermal clip-on#

A thermal imager clipped in front of the objective adds a picture of heat to the tube's. Thermal Clip-On picks what it shows: the Outline of whatever is warm, a Patrol view of anything warmer than its floor, or Full Thermal. A fused goggle draws that over the tube's picture in a colour of its own, so a warm outline stands out against the phosphor: Clip-On Colour, orange to begin with. Set Clip-On Shows to Through The Tube and it goes in through the objective instead, coming out in the phosphor's own colour, as an optical clip-on's does. Clip-On Polarity, Strength, Field, Threshold, Offset and Line Width tune it. Anything drawn into custom depth reads as warm, so turn on Render CustomDepth Pass on the characters you want it to find.

A real overlay is imperfect, and that's tunable too. Clip-On Glow blooms a soft halo round the outlines. Clip-On Detail draws the inside of a warm shape as well as its edge, where its warmth changes: gear, limbs and folds in lines of their own. Clip-On Noise makes the small sensor show: lines that waver, thicken and thin, break up and sparkle. Clip-On Lag lets the clip-on's picture trail the tube's as the head moves, settling back as it stops, as a separate imager's does.

Where next#

• The goggles: every type that comes with the plugin, on the same walk.
• Infrared: illuminators, aiming lasers and strobes that only the tubes see.
• Night vision in your game: lighting a level for it, and the keys a player needs.
• The looks: every Night Vision setting in one table, with what it starts at.