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There are many features of
Dream Cellular, LLC's engineered, lightweight mirror substrates that
make their thermal time constants substantially lower than monolithic substrates. Three of the main features
are listed to the right. We typically compare our substrate to
monolithic substrate the customer might already be using. In
this way exact comparisons can be made so the customer knows;
how much surface increase there is, how quickly each optic cools,
mass comparisons, polishing and gravity displacement comparisons,
etc. We never make generalized statements. They are based on
specific comparisons. |
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* lower
mass |
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* thinner profiles |
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* greater surface area |
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A mass
that can be as much as 4 times lower than a monolithic of the
same dimensions is obviously a large thermal advantage. All things
being equal a small mass will equalize much faster than a large
mass. The small mass is therefore better at following changing
ambient temperatures on smaller scales. A 1C delta between an
optic and the ambient temperature can produce a 0.3-0.5 arc-second
degradation to the images. But this is only one form of degradation.
There are many. Internal
temperature gradients
can also cause degradation.
Understanding all
of these factors is essential for an optimized system and one
that is based on sound engineering and empirical data. Dream
can provide guidance and expertise in not only the cellular optic
but also supporting that optic during tesing and in final use. |
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"Thinner profiles" describes the thickness of a monolithic and
the ribs and any other features in Dream Cellular, LLC's engineered
blanks. A monolithic mirror might be 2.0" thick. Whereas
our cellular substrate might have 0.3" as it's thickest
profile (rib and/or face thickness, etc.). The 2.0" thick
blank has air on either side of the substrate. So one can say
that reaching the center of the glass requires a depth of 1.0"
(half the 2.0" thickness). For the cellular example the
distance to reach the center is only 0.15" or 6.67 times
less than the monolithic. It's far easier for the 0.3" thick
sections of the cellular blank to reach equilibrium than it is
for the 2.0" monolithic. Remember, 0.3" in this example
was the thickest profile within the cellular blank. There would
be other areas that are thinner. All of this is accounted for
when we do CFD (thermal) studies. |
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Just as the profile
thickness affects how quickly a substrate can equilize, so does
surface area. The larger the surface area, the
faster equilization will occur. Dream Cellular, LLC's engineered
blanks routinely have between 3.2 and 4 times more surface area
than monolithics. |
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Individually the
above three main factors each have substantially improvements
over the monolithic substrate. Combined they make an enormous
difference and drastically change long-held assumptions about
specific types of substrates. |
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Even when one of
the three features above is taken away, say the mass, the other
two still make a substantial improvement to the optic. Dream
Cellular, LLC does not have to design for substantially lower
mass. One OEM customer requested a 0.7m
blank that was fairly close to the mass of their existing monolithic.
Dream Cellular's design ended up being 4 times the surface area
and 2 times stiffer than their monolithic. Our blank was about
7% lighter than the monolithic but 2.1 times deeper in side profile. |
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Reaching equilibrium
is only the start. There are applications and environments where
the temperature deltas are quite small. In such cases thermal
issues are less relavant but more than likely still an influence
on the system. However, mass is still a large factor. To learn
more about the mechanical advantages of our engineered cellular
blanks, click
here. |
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Most applications
are not thermally static. For a great many customers following
ambient temperatures with as small of a delta as possible is
a better description than "reaching eqiulibrium." No
matter the substrate material, be it glass or glass-ceramic,
maintaining as small a delta between the optic and the ambient
temperature is key to performance. Dream Cellular, LLC's engineered
cellular blanks can greatly reduce the devastating influence
of mirror seeing. |
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