Hubble Optics Primary mirror 457/2057 Pyrex Enhanced Coating (56562)

Hubble Optics Lightweight Sandwich Mirror

The Hubble Optics lightweight sandwich mirror is a cost-effective and high-performance alternative to conventional solid mirrors and other lightweight designs available on the market. Its construction follows principles similar to those used in the Hubble Space Telescope, combining advanced thermal behavior with excellent structural stability to achieve superior real-world optical performance.

Key Design Advantages

• Thermally and structurally optimized open-core design with a dynamically stable closed back

• Very rapid thermal response, cooling approximately ten times faster than a solid mirror of equal thickness

• Simple flotation mounting for reliable mechanical support

• Around 20% lighter than solid mirrors of comparable thickness

• Exceptional price-to-performance ratio with a Strehl ratio of at least 0.975

Why Choose a Sandwich Mirror?

Telescope mirrors are manufactured under tightly controlled temperature and humidity conditions and are precisely measured only after reaching thermal equilibrium. During the cooling process, temperature gradients within the glass can deform the mirror surface, introducing optical aberrations that are proportional to the coefficient of thermal expansion of the substrate. These gradient-induced aberrations gradually disappear as the mirror cools and stabilizes.

In practice, the main limitation is not surface deformation but the warm air layer directly above the primary mirror. This layer causes image distortion known as “mirror seeing,” which results from variations in air density above the warm mirror surface. No mirror, regardless of glass type, performs optimally until its temperature closely matches the surrounding air. Acceptable performance is typically reached when the temperature difference is below 1 °C, while optimal performance occurs when the difference is less than 0.2 °C.

The goal, therefore, is to bring the mirror temperature to within 0.2 °C of ambient air as quickly as possible. This significantly reduces mirror seeing and improves image quality. For this reason, large professional telescopes use complex cooling systems for their primary mirrors. Research has shown that thinner mirror substrates dramatically reduce thermal time lag, as glass thickness is the dominant factor determining how quickly a mirror reaches thermal equilibrium.

A full-thickness solid mirror may never fully equilibrate during a typical observing session, preventing it from reaching its full optical potential. This is a major reason why the Hubble Optics lightweight sandwich mirror delivers superior performance in real observing conditions, even without active cooling. While fans and other active cooling systems can help, they may also introduce micro-vibrations that degrade image quality if not carefully implemented. The sandwich mirror design reaches equilibrium extremely quickly on its own, providing sharp and stable images sooner.

Technical Specifications

Optical Characteristics

• Aperture ratio: f/4.5

• Focal length: 2057 mm

• Surface reflectivity: 96%

• Optical coating: Aluminum with silicon dioxide overcoat

Physical Properties

• Diameter: 457 mm (18 inches)

• Thickness: 53 mm

• Material: Pyrex glass

Product Information

• Series: Sandwich Mirror

• Category: Parts and spares