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Dream's zeroDELTA

Engineered Lightweight Mirrors


Q u a l i t y

S t a r t s

A t

T h e

S u b s t r a t e
Dream specializes in the design, engineering and in-house production of bubble-free lightweight mirrors using the latest 3D CAD, FEM/FEA, CNC equipment and micro-processor controlled furnaces & annealing ovens. Dream provides cutting edge convex, concave and plano mirrors that eliminate the performance losses associated with solid mirrors.
The CTE of Dream's lightweight mirrors is 3.16x10-6/°K. Dream does not use plate glass, which has a CTE almost 3x higher (9.1x10-6/°K) and is nearly 4x more sensitive to bending due to thermal transients; internal temperature gradients warping the figure of the optical surface.


Dream's zeroDELTA lightweight mirrors were developed through our casting technology. Prior to developing this technology fusing and frit bonding technologies were investigated. Those techniques use individual glass components that are cut, assembled, then fused or frit-bonded together at lower temperatures. These methods have fundamental hurdles that make it extremely difficult to vary specific rib thicknesses, create varying sub ribs, tapered ribs, etc. Dream's cast technology offers far more design freedom and therefore far greater optimization than other methods. The ability in optical design to use an asphere, not being confined to spheres only, is a good analogy. Dream's cast technology does not have inherent limitations.

Dream's mirrors are cast (melted) to produce a single, continuous mirror that does not suffer from the historically significant problem of bondline issues, which is why Dream chose not to pursue less expensive, lower temperature fused and frit-bonded mirrors. Since Dream's mirrors are cast they don't need expensive inspection equipment, techniques and expertise in order to uncover areas of the mirror where less than 100% bonding took place. Dream's mirrors don't have to "act" like one piece of glass. They ARE one piece of glass. They won't come apart today, tomorrow or 50 years from now. Remember, the optical surface of the mirror is typically finished to fractions of a wavelength of light. The mirror doesn't need to come apart in order to have problems.

The zeroDELTA lightweight mirrors are not pocket-milled from a solid mirror blank either. Pocket-milling is limited in its design freedoms for; rib types, depths, shapes, radii in corners, etc. Pocket-milling is typically 6-10x more expensive than Dream's technology and it tends to leave mass concentrations at the node of ribs.

Dream started optimizing lightweight mirrors back in 2003. No other company in the world has our accumulated experience; design & engineering, casting & annealing, grinding & polishing/finishing, as well as using & testing them firsthand in Dream's finished telescopes. This vertical integration brings an extensive knowledge base due to nearly 15 years of engineering & experience working with lightweight mirrors, as well as dedicated carbon fiber mirror mounts and athermal carbon fiber telescopes. In this way we have closed the design and engineering loop because we do not simply produce lightweight mirror blanks, we process them (generation, grinding and polishing) and use them in full instruments.

This broader-based, real-world (empirical) knowledge, coupled with vertical integration of all tasks related to processing of the mirrors, allows Dream to maximize the mirror's design & features in every way. We feed what we learn back into the designs and have been since 2003. Dream is creating mirrors that are not just light, stiff and with a much shorter thermal time constant, but functional and optimized to a degree never seen before.

"We shall look back and see how inefficient, how primitive it was to work with thick, solid mirrors, obsolete mirror-curves, ..."
- George Willis Ritchey 1928: JRASC, Vol. XXII, No. 9, November 1928.
 


Print Through

definition, interferometry examples and information

Thermal Advantages

mirror seeing & the boundary layer

Mechanical Advantages

examples of mechanical advantages offered


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