The Inspiration for the OA-Series ™
Thank you for your interest in DGM Optics™, OA-Series™ telescopes. The OA-Series™ telescopes are a result of 8 years of design and development with 6 years of field-testing and comparison with a variety of commercial and amateur built instruments. They also represent the insights I’ve gained through 15 years of experience in the field of commercial optics as a Thin Film technician and as a Research and Development technician in the field of fiber optics.
Most astronomers are familiar with the razor sharp, high contrast images offered by refractors, but also are aware of the very high cost of these scopes, particularly if they are the so-called apochromatic instruments. It is the freedom from obstruction in the light path that is a very significant reason for the superb resolution offered by refractors. Knowing that, the question I, and probably a million other astronomers, asked was; “Would an unobstructed reflector system have similar qualities?”
Analysis of Other Mirror Systems
There are a number of unobstructed reflector systems already in use, most notably the tilted component designs such as Schiefspieglers, Yolos, and a host of other unusual 3 and even 4 mirror systems. These designs do feature excellent images, however they can tend to be somewhat user-unfriendly, with corrective second, or even third elements that require extremely precise and often difficult alignment. They also utilize F/ ratios of 15 or greater, fine for lunar or planetary, but resulting in a very narrow field of view. Another approach is the use of an off-axis mask, but the primary mirror must be free of zones. In addition to that, the scope must be slightly realigned in order to direct the diffraction-limited area to the center of the field of view. Also, this scenario still retains the big mirror thermal disadvantages.
Some the most popular designs in today's market are the compound element systems such as the Maksutovs and Schmidt-Cassegrains, and with good reason. They offer compact design and portability, which are strong selling points. However, if you do the simple transmission/reflectance equation I will present, you’ll find the typical system will have lost 15-20% of its effective optical throughput before it even reaches the focuser. If you own or are considering owning one of these instruments, determine the transmission or reflectance of all the optical elements in the system, then express the value(s) as decimals and multiply them. An example of the equation would be .98 x .95 x .95 x .95 = .84. So an 8-inch SCT ends up with a 16% optical throughput loss at the focal plane. This is assuming 4 elements with transmission/reflectance values as stated. Lesser values will rob the system of even more energy, and, the equation does not include losses caused by diffractive effects and central obstruction.
Why Choose The OA-Series Telescopes?
Telescope makers often claim optics that meet "diffraction limited" criteria. However, careful optical testing using laser interferometry reveals that many of these instruments do not meet that fundamental standard of optical quality. This is especially true of mass produced instruments. DGM Optics’™ primary mirrors are produced by Dodgen Optical. Dodgen Optical has specialized for many years in space qualified, on and off axis, parabolic and hyperbolic optics, producing superb systems for a variety of government and commercial customers.
Typical wavefront values for the OA-Series™ telescopesare a minimum of 1/8 wave peak to valley, RMS 1/40 wave, or better, and Strehl Ratio approaching 99%. Each mirror’s figure is determined by laser Interferometry. Use of these highly sophisticated, extremely sensitive instruments, further ensures a smooth, consistent figure, and superb image quality from each OA-Series™ telescope. All optics are produced with fine, annealed, low expansion Pyrex glass.
Why then consider one of DGM Optics™, OA-Series™ telescopes? The answer is resolution! OA-Series™ scopes offer some of the finest optical images you will see with any telescope of any design ! Images of the major planets will astound the observer in revealing the same detail as significantly larger instruments. Lunar detail is tack sharp, rekindling long lost interest in lunar viewing. But the OA-Series™ instruments are not limited to only superb, lunar, planetary, and double star work. The views of nebula, galaxies, and clusters are significantly enhanced due to a very dark, scatter-free background. The moderate F/ ratios (10 average) of the OA-Series™ telescopes allow the use of long focal length eyepieces and the attainable true field of view ranges from approximately 1.6 to 1.8 degrees.
Alignment and Materials Used for OA-Series Telescopes
Are the OA-Series™ telescopes difficult to align? Not at all, in fact OA-Series™ scopes are easier to align than classic Newtonians instruments and, are not tilted component designs and therefore do not require corrective secondary mirrors. Complete systems and tube assemblies are shipped with the secondary mirrors permanently aligned. The primary is then mounted in the tube assembly and is easily aligned in just a few minutes. Unlike traditional on-axis Newtonians, the secondary mirror is mounted on a rigid “L” shaped stalk and will maintain alignment even during the most abusive handling. If you need more information on alignment, Click Here to view DGM Optics’ new online “Use and Care” manual which contains a detailed tutorial on alignment and other detailed information about the OA-Series™ telescopes .
What about the mounted systems? The DGM Optics™ dobsonian mounts are constructed with a high quality, 5 ply Atlantic birch and triple coated with a clear polyurethane. Bearings are custom manufactured using UHMW (Ultra-High Molecular Weight Polyethylene), riding on Teflon, and feature very smooth vertical and horizontal motion. Then, to make viewing sessions as comfortable as possible, the tube of the OA-Series™ instruments are set in a hinged split yoke with an adjustable draw latch enabling the tube to be balanced and rotated for a “no neck strain” night of observation.
Tube Options
Up until now Sky Valley Scopes has supplied the majority of tubes for OA-Series Ō scopes larger than the OA-4.0. Unfortunately due health problems, Sky Valley Scopes owner Ken Ward will no longer be able to supply these superb tubes for the OA-Series ä instruments. DGM Optics is grateful to Sky Valley Scopes for supplying us these fine tubes for over 4 years and wish Ken and family all the best.
Note: The Sky Valley Scopes fiberglass tubes were an important component regarding the OA-9.0 as it used a “cut” tube for that instrument. Please contact DGM Optics for tube options regarding the OA-9.0.
The new default tubes for the OA-Series ä are the California Tubular Designs (CTD) aluminum pattern wrapped tubes. CTD tubes are available in a variety of interesting patterns and designs and typically are delivered in less than 4 weeks. Other tube choices include Pacific-Works carbon fiber and Parallax aluminum tubes.
I sincerely believe the OA-Series™ telescopes are filling a long standing void in amateur astronomy by offering high resolution and contrast , a moderate field of view, without the high price tag of refractors. Factoring in the absence of a central obstruction and the use of durable standard reflectance coatings, you’ll find the OA-Series™ telescopes outperform classic Newtonian instruments of considerably larger aperture. The image quality, construction, and other highlighted features of the OA-Series™ telescopes make them one of the best values available to the amateur astronomer today.
Sincerely,
Daniel G McShane
Daniel G. McShane, President
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DGM Optics Charlestown, NH (Call or e-mail for street address) |
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(978) 874 2985 |
