WWW.ASTRONOMY.COM 63uncommonly high optical standards.
Customers can expect triplet lenses to have
Strehl ratios of 0.98 or 0.99. A theoretically
perfect lens has a Strehl ratio of 1.0.
Lens creation
Stellarvue is constantly experimenting with
optical designs to improve their already
excellent products. Let’s follow the process
of making one of the company’s high-end
telescope lenses.
It begins with a square or “strip” of
high-quality glass from Ohara. Once the
theoretical curves are known, the informa-
tion is fed into the Haas VF3 CNC
machine, where diamond-cutting tools
shape the blank and cut it to the correct
thickness. Tiny ridges left from the tools
are removed by grinding the blank and
then polishing it using ever-finer grits.
It’s then checked against a test plate
that has accurate opposite curves; when
the interference lines are straight, the lens
has the correct curve. The lens is then
checked under a microscope for any
physical imperfections.
Once all three lenses (for an air-spaced
triplet) have been manufactured, they are
mounted with the correct spacers and
taken to the interferometer for inspection.
Specifically, the lens assembly is tested for
zones, trefoil, astigmatism, spherical cor-
rection, and Strehl ratio. Imperfections are
corrected by hand polishing until the lens
assembly delivers an extremely high per-
formance. Once the prototype has passed
all the internal tests, it is then tested visu-
ally and photographically on the sky.
Stellarvue’s standard lens production is
much the same, except the process begins
with a glass disk that has already been
formed to the basic shape of the finished
product by the glass manufacturer. All
telescopes with the “SVX” label have
been hand-corrected to the highest stan-
dards possible.
Previously, the company made triplet
lens assemblies that were oil spaced. This
made the manufacturing process easier
because the lens assembly contains two
surfaces that act as one. So in all, you only
have to create four corrected surfaces.
An air-spaced triplet, however, has six
corrected surfaces, which allow for a much
higher degree of correction. Stellarvue uses
the highest-quality anti-ref lective multi-
coatings that go well above and below the
visual spectrum. Because Stellarvue tele-
scopes are used photographically with
CCD cameras, and because CCDs typicallyrecord outside the visible spectrum, this
helps eliminate ghosting.Everything must work
As Maris has often said, it’s not enough
to manufacture superb optics — the lens
elements need to be properly supported by
the telescope. Lens cells must hold them
in perfect alignment without pinching the
glass when the temperature plummets.
Adhering to the same standards as its lens
making, Stellarvue has invested a great
deal of research into how to properly hold
the lens elements.
Maris is surrounded by a crew of dedi-
cated associates who are involved with
every aspect of telescope creation. Working
at Stellarvue is a progressive experience
because telescope design and manufactur-
ing keeps evolving to create better instru-
ments. This is especially true when all
elements of the telescope are manufactured
in-house to such high standards.
One day I’d love to add a 6-inch
Stellarvue refractor with an air-spaced
triplet that has a Strehl ratio of 0.99 to my
telescope arsenal. Using equipment of this
quality is like no other experience.
Perfection in astronomy is everyone’s
dream — including mine.One of the world’s top astroimagers,
To ny H a l l a s is a contributing editor of
Astronomy who loves high-quality telescopes.LEFT: Once the components that will go into
Stellarvue’s refractors are created, Liz Ruiz
gets them ready for assembly.
ABOVE: Steve Fraticelli inspects each lens,
under high magnification, for defects.
RIGHT: The main crew at Stellarvue includes
(left to right) Ruiz, Maris, Fraticelli, Mayer,
and Ryan Rodriguez.