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TECHNICAL INFORMATION ON ASA NEWTONIAN ASTROGRAPHS
ASA (Astro Systeme Austria) astrographs were developed based on the experiences of
some of astronomy's best astrophotographers. They were designed using uncompromising
optical and manufacturing principles. Using the best quality materials available in the industry, ASA engineers have developed a series of products which leave nothing to chance.
ASA astrographs offer perfect imaging performance covering a large field of view, fast focal
ratios, exquisite optics, easy camera adaptablility, and lightweight but very stable construction! ASA astrographs are the perfect starting point for serious astronomers who wish to
implement a reliable and convenient telescope system for doing astrophotography.
All ASA Newtonian astrographs have optics of Schott Suprax, a borosilicate glass, which
Schott classifies as chemically and thermally resistant. ASA mirrors are individually tested
using a Zygo interferometer, and must meet specs for a mirror surface polish figure of <1/7
of a wave Peak-to-Valley (P-V). They use advanced coatings which provide 97% reflectivity.
This also includes their flat mirrors. (By requesting a special order, primary mirrors made
using Sitall, also commonly known as Astrositall, a crystalline glass-ceramic, manufactured
by LOMO, Russia can be provided by ASA. This material has an extremely low coefficient
of thermal expansion. However, ordering this product may incur a longer delivery time.)
This manufacturerʼs uncompromising optical design by Philipp Keller, PhD. Physics, and
their use of the finest materials and modern manufacturing practices, yields imaging results
that satisfy the most critical astrophotographer. Testing has shown that these instruments
produce the finest stellar spot sizes obtained with currently-available fast telescopes, when
ASA corrector lenses are used with the basic astrograph Optical Tube Assembly (OTA).
The new "double thin spider" design, now supplied with ASA N-Series Newtonian style
astrographs is rigid while significantly reducing annoying diffraction spikes from bright stars,
normally caused by the spider! ASA's astrograph product line is an astrophotographer's
dream come true!
ASA Newtonian style astrographs are sold in two different models: The N-series use a
parabolic primary mirror, while the H-series use a hyperbolic primary. All of the N-series
models can be obtained without a corrector lens if desired. If you prefer to use one of ASA's
excellent correctors, these can be purchased separately. The field corrector lenses will
handle the largest CCD arrays currently popular. All of the ASA corrector optics provide
sufficient backfocus (flange focal distance) in combination with a wide, well-corrected flat
image circle. While it is possible to use these Newtonian astrographs without a corrector
lens in theory, the result will be some unavoidable reduction in image quality in your CCD
camera images. Without a good corrector, no astrograph will deliver optimum results. ASA's
correctors are optimized for an extra-wide bandwidth of 400 nm to >700 nm. Every lens
used in the corrector is measured to verify its surface radius & thickness, before itʼs used in
assembling a lens system. (OPT strongly suggests that our customers who purchase an
ASA astrograph also plan to use an appropriate ASA corrector lens with their OTA.)
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ASA Newtonian astrographs all use a fast optical system (hence a small f/#) and are capable of working at multiple focal lengths. This means you can achieve good signal-to-noise
ratio with your CCD using short exposure times. The N-series astrographs all have a natural focal ratio of f/3.8, without a corrector lens. Their system f/# can be reduced or extended
easily by the user, so the natural focal length of the device can be shortened by a factor of
0.75x or increased by a factor of 1.8x, while at the same time retaining the highest-quality
imagery. You can enjoy all three telescope focal lengths, simply by using each of the three
appropriate corrector lenses. These correctors all have been designed and fabricated
specifically to maintain the best stellar image-spot energy distributions, consistent with the
basic ASA telescope optics in use, as well as providing flat image planes, over the useful
field. These criteria are exactly what the astrophotographer wants to provide for their CCD
camera. For example, by installing the 3 inch Wynne Corrector lens (standard with the Nmodels), you can achieve a focal ratio of f/3.6. With the 2 inch or 3 inch Reducer, a focal
ratio of f/2.75 will result. Using the ASA Barlow Flattener Corrector, the resulting focal ratio
will be f/6.8.
ASA astrograph tube assemblies are manufactured of sandwiched carbon fiber. Carbon
fiber technology adds to the astrograph's visual appeal, while making them approx. 60%
lighter. Thanks to the thermal stability of carbon fiber, your focus remains stable over a long
period of time. The tube assembly's stability means the optics remain collimated longer.
Speaking of collimation, the primary mirror of the ASA Astrograph includes a center triangular reference mark for ease of collimation. The internal surface of each tube assembly is
also treated with black velvet, to reduce scattered light. ASA astrographs use Newtonian
output ports which are compatible with 3 in focusers. The ASA product # A2-OK3 electronic
motorized focuser is the ideal focuser to use with all models in their astrograph line.
ASA Newtonian astrographs are available in various aperture sizes. These include:
the 8N (8 in), the 10N (10 in), the 12N (12 in), the 16N (16 in) all of which use closed-tube
designs, and the 20N (20 in) model which can be obtained in a closed tube or partiallyopen truss-tube design. All these models incorporate the same natural f/3.8 focal ratio,
while providing different focal lengths. All are compatible with the same focuser unit as well
as all the N-series ASA corrector lenses. See the attached table from ASA, which provides
specifications for all six models of the N-series Newtonian astrograph telescopes.
The H-series astrograph, currently available only in 8 in aperture, differs from the N-series
in that it uses a hyperbolic primary mirror. The ASA 8H also is made with an integral preinstalled corrector lens and electric focuser unit. The 8H provides the user with stellar spot
sizes which are smaller than the N-series, and works at faster speeds. The optical system
resolution is higher overall. Providing a fast focal ratio of f/3.0 and a perfectly corrected field
out to 60 mm diameter, this astrograph is the ultimate wide-field-photo and sky survey
instrument. This instrument is being used for professional search-and-discovery survey
applications, and both amateurs and professionals will appreciate this fine astrograph.
See the attached table from ASA, which provides their specifications for the ASA 8H.
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Please Note: If you purchase only the ASA Optical Tube Assembly (OTA), the corrector lenses
must be purchased separately. Correctors and the electronic focuser unit are not normally supplied
when purchasing an OTA.
Because ASA telescopes are made in Austria and must be imported, there are some shipping considerations which customers may wish to discuss with OPT when placing an order. Please email
OPT at: [email protected], or give one of our telescope experts a call at 1-800-483-6287,
if you have questions regarding pricing, sales, technical matters, or shipping details.
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Note: Except for “Aperture,” all quantities in these tables are given in metric units. All values are
subject to change at any time, at the discretion of the manufacturer of these products, Astro
Systeme Austria (ASA). All data shown in the tables above were provided to OPT by ASA.
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