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REDEFINING INSTALLED PERFORMANCE |
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of---o-p-t-o---m-e-c-h-a-n-i-c-a-l---s-y-s-t-e-m-s--est 2003 |
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16"
Dream Astrograph - Filtered
Air System Technology (FAST™) |
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On the previous page the
many benefits of Dream's FAST™ system
were discussed. We will go over a few of the reasons why Dream
has developed such a system to deal with the thermal issues inside
the Optical Support Structure (OSS). |
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Knocking down (but not eliminating) the
boundary layer, that thermal gradient layer just above the optical
surface, is proven to reduce mirror seeing. Unfortunately this
merely acts as a Band-Aid, covering up the real problem. It is
the temperature gradient between the optic and ambient temperature
that's causing the issues at the boundary layer. Internal temperature
gradients within the optic itself are also causing a separate
problem in non-zero-expansion glass types; Pyrex, Borofloat 33,
plate glass, etc. Internal temperature gradients distort the
figure of the optic. For a 16" optic that is 2" thick,
a 1°C internal gradient will distort the figure of that optic
by roughly 1/3rd wave (~183nm of distortion, at the surface,
not wavefront). This is why knocking down the boundary layer
is not enough. The figure distortion will persist until the optic
is within +0.1°C to -0.2°C of ambient temperature, which
is typically dynamic (ever-changing), not static. |
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Even a thin monolithic mirror, which is substantially more difficult
to support without causing cell-induced astigmatism (yet another
form of performance-robbing), takes a substantial
amount of time to "equalize" when compared to Dream's
engineered
zeroDELTA™ lightweight
mirrors. Dream's mirrors have an independently tested
CTE that is 23% lower than Pyrex, Borofloat 33, etc., but due
to their thin features offer world-leading
performance. |
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Dream has never
masked the historic thermal & mechanical problems of opto-mechanical
systems. |
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Dream has dealt
with them directly. |
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Dream's use of FAST™, since 2003,
provides numerous benefits, especially when combined with Dream's
engineered
zeroDELTA™ lightweight
mirrors. This same system originated in a 10"
f5 telescope. The extensive use of CF and CFSC™
to produce incredibly stiff, lightweight support structures that
very closely match the Coefficient of Thermal Expansion (CTE)
of the mirrors (athermal) means that Dream's telescopes are at
the pinnacle of performance. |
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Dream is the only company in the world utilizing FAST™. Dream is also the only company
in the world offering a standard optical instrument that utilizes
engineered lightweight mirror blanks for both the primary and
secondary mirrors. This combination produces unrivaled speed
in equalization of the optics and the ultimate in installed performance. |
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Click either image
to see examples of the quality inherent in Dream's telescopes. |
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Each instrument is fully tested under the stars prior
to shipping. |
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