Hubble Optics Primary mirror 508/1880 Pyrex Enhanced Coating (56558)

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 deliver superior optical performance in real observing conditions.

Key Design Advantages

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

• Extremely 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 the same thickness

• Outstanding 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 aberrations gradually disappear as the mirror cools and stabilizes.

In practice, the primary limitation is not surface deformation but the warm air layer directly above the 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 at its best 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 objective, therefore, is to bring the mirror temperature to within 0.2 °C of ambient air as quickly as possible. This greatly 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 in 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 key reason why the Hubble Optics lightweight sandwich mirror delivers superior performance in real-world 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 much sooner.

Technical Specifications

Optical Characteristics

• Aperture ratio: f/3.7

• Focal length: 1880 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