Engineers Create Lightweight Multi-Color Fresnel Lens for Telescopes

taylorvich writes:

https://phys.org/news/2025-02-flat-telescope-lens-capture-faraway.html

Scientists have long searched for a way to reduce the weight of lenses without sacrificing functionality. And while some slimmer alternatives exist, they tend to be limited in their capacity and are generally challenging and expensive to make.

New research from University of Utah engineering professor Rajesh Menon and colleagues at the Price College of Engineering offers a promising solution applicable to telescopes and astrophotography: a large aperture flat lens that focuses light as effectively as traditional curved lenses while preserving accurate color.

The study, "Color astrophotography with a 100mm-diameter f/2 polymer flat lens," appears in Applied Physics Letters.

This technology could transform astrophotography imaging systems, especially in applications where space is at a premium, such as on aircraft, satellites and space-based telescopes.

[...] Lenses bend light to make objects appear larger. The thicker and heavier the lens, the more it bends the light, and the stronger the magnification. For everyday cameras and backyard telescopes, lens thickness isn't a huge problem.

But when telescopes must focus light from galaxies millions of light-years away, the bulk of their lenses become impractical. That's why observatory and space-based telescopes rely on massive, curved mirrors instead to achieve the same light-bending effect, since they can be made much thinner and lighter than lenses.

Scientists have also tried to solve the bulkiness problem by designing flat lenses, which manipulate light in a different way.

One existing type, called a Fresnel zone plate (FZP), uses concentric ridges to focus light, rather than a thick, curved surface. While this method does create a lightweight and compact lens, it comes with a tradeoff: it can't produce true colors. Rather than bending all of the wavelengths of visible light at the same angle, the ridges of an FZP diffract them at different angles, resulting in an image with chromatic aberrations, or color distortions.

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