Hubble Optics Primary mirror 508/2134 Pyrex Enhanced Coating (56563)

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 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 deliver superior optical performance under real observing conditions.

Key Design Advantages

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

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

• Simple flotation mounting for reliable and stress-free support

• Around 20% lighter than solid mirrors of the same thickness

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

Why Choose a Sandwich Mirror?

Telescope mirrors are manufactured in tightly controlled temperature and humidity environments and are precisely measured only after reaching thermal equilibrium. During cooling, temperature gradients within the glass can deform the mirror surface, creating optical aberrations proportional to the coefficient of thermal expansion of the substrate. These gradient-induced aberrations diminish as the mirror cools and stabilizes.

In practical observing, 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 that of the surrounding air. Adequate performance is typically achieved when the temperature difference is below 1 °C, while optimal performance occurs when the difference is less than 0.2 °C.

The objective is therefore 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 rely on 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-world observing, 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 much sooner.

Technical Specifications

Optical Characteristics

• Aperture ratio: f/4.2

• Focal length: 2134 mm

• Surface reflectivity: 96%

• Optical coating: Aluminum with silicon dioxide overcoat

Physical Properties

• Diameter: 508 mm (20 inches)

• Thickness: 53 mm

• Material: Pyrex glass

• Total weight: 15 kg

Product Information

• Series: Sandwich Mirror

• Category: Parts and spares