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Comparison of outside optician's "smooth"
finish versus Dream's re-finish of the same surface/mirror (click image). |
"The original mirrors
finish was horrible. You have done an excellent job in improving
the finish." |
- Dream customer |
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RMS Surface Roughness Data (smallest
scale errors) |
from Dream's in-house polishing |
Concave 247mm
CA, f2.27 |
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The above RMS surface roughness
test was conducted in the mirror's center, showing an average
of 6.42Å. |
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The above RMS surface roughness
test was conducted at roughly the 50% zone of the mirror, showing
an average of 7.39Å. |
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Dream averages 6-9Å RMS surface roughness,
which is 2.2-3.3x better than the industry standard spec for
visual spectrum of 20Å. |
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**Dream's founder, Shane Santi,
ground and polished his first mirror in 2001. Since Dream was
established in 2003 it has evolved into a more vertical company
that has leveraged its expertise in designing and engineering
the zeroDELTA
lightweight mirrors into fully processing, including finishing,
these high-performance and ground-breaking modern mirrors. Dream's
extensive use of modern engineering tools and intelligent design
breaks the paradigm that most associate with lightweight mirrors.
Numerous examples over the years have proven that Dream's high-level
of engineering and expertise allows the zeroDELTA mirrors to be processed with conventional
methods and to a finish equal to that of solid mirrors, without
the baggage that comes with solid mirrors. |
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**This
paper shows an example 396mm CA, f1.376
mirror finished with low Mid-Spatial Frequency (MSF) errors,
as well as low RMS surface roughness. |
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**The below high resolution interferometry
data from a 415mm, f3 concave paraboloid shows how smooth (extremely
low Mid-Spatial Frequency errors (MSF, historically called primary
ripple)) are in a Dream zeroDELTA engineered lightweight mirror when processed
by Dream. The zeroDELTA
mirror had a face of roughly 0.1" thick. This is a superb
example of why real and extensive engineering matters, setting
Dream mirrors apart from others. The band number is defined toward
the top of the graphic, giving a description of the physical
size of MSF error being evaluated in that column. |
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**The above
primary mirror was used inside a Dream Cassegrain telescope for
IR use. The 2-mirror portion of the telescope achieved 0.83 arc-second
image resolution from less than an ideal location. See this telescope
within this
white paper. Dream
finished this aspheric primary mirror to within 0.009% of the
nominal radius. Our typical radius tolerance is +/-0.1%, but
as this example shows, we can achieve far tighter. |
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**Dream's
dedicated polishing and testing room is 68°F, +0/-2°F
year-round. Although Dream's zeroDELTA lightweight mirrors equalize exceedingly fast,
the tight temperature control is ideal for test equipment repeatability,
as well as consistency & control of the engineered pitch
& polishing compound that Dream uses. |
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Click on the image to the left to gain access to both extraordinary
videos and test images from a 20" f3.5 zeroDELTA mirror finished January 4th, 2018, during
record cold temperatures. |
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**The ceiling
of the room is equiped with a 44" x 44" trapdoor that
allows vertical testing of mirrors. This can allow comparative
data of the mirror performance in the final mirror mount at different
angles. It can also allow finishing of a primary mirror in its
final mirror mount, an ideal way to ensure the highest quality
and performance in final use. |
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Click the image to the right
to see the quality and tight specifications that can be achieved
on a convex secondary mirror. Dream can also provided dedicted
athtermal carbon fiber mirror mounts and finished telescopes. |

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