Your eyes are focusing on something that isn't there.

01 · The floating screen

A magnifying glass, aimed at your eye.

Your eye can't focus closer than about 10 cm, so the display sits just inside the focal length of the lens. The light leaves the lens spreading as if it came from a much bigger screen far away, and your eye relaxes onto that virtual image.

Move the display a fraction of a millimetre and the image moves by metres. That is why lens-to-display alignment is set in microns on the line.

02 · Folding the light

Why new headsets got thinner.

A plain lens needs the full distance between screen and lens. A pancake lens folds it: a half mirror and a reflective polariser bounce the light back and forth, so it crosses the same gap three times.

The cost is brightness. Each meeting with the half mirror loses half the light, so at most a quarter reaches your eye.

03 · Pixels per degree calculator

Resolution means nothing without the angle.

Your eye judges pixels per degree: how many pixels sit inside each degree of your view. Normal 20/20 vision resolves about 60. Most headsets sit well below that: see every headset on one chart.

The display shows our calibration chart, rendered at the sharpness you choose. In macro view each colour pixel is drawn as its red, green and blue subpixels, the way a close-up photo through a headset lens shows them. In mono green, each pixel is a single green emitter.

04 · Light trapped in glass

Why AR glasses show a small window.

AR glasses pipe the picture in from the temple. Light enters a thin sheet of glass and stays trapped by total internal reflection, bouncing along until a grating releases it toward your eye.

The glass stays the same size. What changes is how wide a picture it can carry: the floating window is how big the AR screen looks to you. Higher-index glass traps a wider range of angles, so the window grows.

Switch the light to mono green and the window jumps. One grating bends each colour by a different angle, so full colour has to share the same range of angles. That is why colour AR glasses stack two or three plates, and why green HUD glasses can be thinner, brighter and wider. To compare the main waveguide types, read Choosing a Waveguide Architecture; for the physics in depth, What Is a Waveguide Display? Our optical design work covers custom waveguides and light engines, designed to a customer's spec.

05 · Two distances at once

Why your eyes get tired in VR.

In the real world your eyes do two things together. They turn inward to point at an object, and they refocus to its distance. Your brain has wired the two together since childhood.

A headset breaks that link. The 3D picture tells your eyes where to point, but the lens puts the screen at one fixed focus, usually somewhere around 1.3 to 2 metres. Bring an object close and your eyes point near while focusing far. That mismatch is a known cause of eye strain in VR.

06 · Fit and the eyebox

Why a headset has to fit your eyes.

Each lens only works from a small zone behind it, the eyebox. With your pupil at its centre, you see the whole picture, sharp. Move off-centre and the edges soften and colours start to split. Leave the eyebox and the lens rim cuts into the picture.

Adults' eyes sit roughly 54 to 72 mm apart. A headset with fixed lenses is built for the middle, so people at either end look through the edge of every lens. Set your eye spacing, then drag the view to move your eye.

07 · Foveated rendering

Draw it sharp only where you look.

Only a small patch at the centre of your vision, the fovea, sees fine detail. Everywhere else, your own eye blurs the picture. A headset can use that: full detail where you look, far fewer pixels everywhere else, and the graphics chip saves the work.

Try it. Keep your eyes on the pointer and the drop in quality is hard to spot. Look anywhere else and it jumps out. With eye tracking, the sharp zone follows your gaze, so you never catch it.

08 · Every headset

The whole industry, on one chart.

Field of view against sharpness for 51 headsets and glasses, including our own products. Wide and sharp is the hard corner: every product trades one for the other.

Sharpness here is the average across the view: pixels across one eye divided by the horizontal field of view. Makers often quote the centre, which is higher (how to read an XR spec sheet). Hover a point for details.