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Hubble Optics Primary mirror 355/1778 Pyrex Enhanced Coating
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Hubble Optics revolutionary lightweight sandwich mirror is a cost effective and superior alternative to other lightweight and solid mirrors available on the market. The Hubble sandwich mirrors are designed and built in a similar style to the Hubble Space Telescope, the most advanced telescope ever built.
- Thermal and Structural optimized open core, and dynamically stable closed back design
- Rapid Thermal Response: cools down about 10 times faster than a solid mirror of equal thickness.
- Simple Flotation Mounting
- Lighter than the solid mirrors (with weight saving about 20% comparing with the solid mirrors of equal thickness)
- Cost competitive and unprecedented price/performance ratio: Strehl Ratio >= 0.975
Why would you select a Sandwich Mirror?
Telescope mirrors are manufactured in a strictly controlled temperature and humidity environment. Each mirror is carefully measured after it has reached equilibrium. While cooling, gradients in the mirror will cause deformation of the surface, and the aberrations induced by these gradients will be proportional to the CTE of the substrate. These gradient-induced aberrations die out as the mirror cools and equilibrates.
The main problem is not the aberrations due to deformation, but the layer of warm air in front of the primary mirror. This layer of warm air is the main cause of the image distortion called “mirror seeing”, which is caused by the non-uniform index of diffraction in the cooler air over the warm mirror surface. No mirror, regardless of the type of glass used, will perform adequately until the mirror is close to the temperature of the ambient air. This occurs when the temperature difference between glass and air is less than one degree centigrade (°C), and best performance is achieved when this difference is less than 0.2 °C.
Therefore, the goal is to bring the temperature of the mirror to within 0.2 °C of the ambient air temperature as quickly as possible. This will greatly reduce image distortion due to mirror seeing. This is why all large professional mirrors, regardless of the type of glass used, employ complicated cooling systems to cool the primary mirror. For example, the Advanced Technology Solar Telescope (ATST) 4.24-meter primary mirror uses a jet cooling system.
Based on the extensive research, ASTS concluded that “thinner substrates dramatically reduce the thermal time lag”, Technical Note #0028 by Nathan Dalrymple. For any mirror, cross sectional thickness of the glass is the primary factor in determining the thermal time temperatures during observing or imaging, your full thickness mirror may never reach equilibrium, and never reach its full optical potential. This is one of the major reasons why Hubble Optics lightweight-sandwich mirror has superior optical performance in real world situations, even without an active cooling system. (Active cooling systems, such as fans, introduce their own serious problems, such as micro vibration, which can seriously degrade the image quality if not done correctly.) Hubble optics mirrors reach equilibrium extremely fast, and without aid.