Optique
Fresnel lens
Également appelé Fresnel optics, god rays
A Fresnel lens is a thin, light lens made of concentric ridges; it is cheap and bright but can show glare streaks called god rays and a smaller sharp area in the center.
A Fresnel lens (pronounced "freh-NEL") replaces the thick curved surface of a normal magnifying lens with a series of thin concentric rings. Each ring bends light like a slice of a full lens, so the result is much thinner and lighter. For years this made Fresnel lenses the standard choice for consumer VR headsets.
Strengths
- Low cost and low weight.
- Good light efficiency, so the image is bright without a very powerful display.
Weaknesses
- God rays: streaks or halos around bright objects on dark backgrounds, caused by light scattering off the ridges.
- A smaller sweet spot: the image is sharpest in the center and gets blurrier toward the edges, so fit and IPD matter more.
- A deeper headset, because the display must sit farther from the lens than with a pancake lens.
Where you find them
Fresnel lenses are still used in lower-cost and older headsets, such as the Meta Quest 3S, the Meta Quest 2 and the PlayStation VR2.
Termes associés
- Pancake lens
- A pancake lens is a folded optical design that bounces light back and forth between layers…
- Screen-door effect
- The screen-door effect is a visible fine grid of dark lines between pixels in a VR headset…
- Interpupillary distance (IPD)
- Interpupillary distance (IPD) is the distance between the centers of your pupils…
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