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Orion Optics OMC300 O.T.A.
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High Resolution Tube - Subaperture Maksutov Cassegrain - Compact Design
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- Optical Design: Sub Aperature Maksutov Cassegrain
- Focal Length (Ratio): 2700mm (f/9)
- 1/4 PV wavefront optics or better
- Quality 2" Crayford focuser
- Simple collimation mechanics
- Full length dovetail plate
- Optional:
- Deluxe 1/6 PtV wavefront optics and Hilux coatings
- 50mm Finder Scope
- Field focal reducer to f5
- Sky-Watcher PRO or Vixen SPHINX mount
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OMC300 on ATLUX mount.
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Outline
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The OMC300 has a compact high resolution tube and the substantial,
fully computerised, Vixen ATLUX mount and Tripod are undeniably
one of the best combinations available in terms of reliability,
quality, accuracy and price.
The four vane stainless steel, ultra rigid spider is held and collimated
by a revolutionary, PCS system for accurate, reliable collimation.
PCS (Peripheral Collimation System) allows collimation several times more
accurate than normal SCT and other Cassegrain systems. Collimation is precisely
held by means of the PCS geometrically designed components, ensuring images are
as perfect from one night’s viewing to the next.
Two dovetail receivers are fitted and allow either the attachment of a 50mm
finder scope (supplied) or a camera for direct sky photography. Both are
interchangeable.
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Orion Optics OMC, front and rear view.
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JMI Focuser
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The JMI NGF is a 2" black-anodized aluminum focuser designed for use on
6" to 16" Schmidt Cassegrain Telescopes (SCTs). It includes an SCT
threaded output adapter to allow use of standard SCT equipment. The NGF-C lifts
up to 8 pounds. The focuser gives 1/2" of travel and is designed for fine focus
after rough adjustment with the normal telescope focuser knob.
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The JMI Next Generation Focuser (NGF) is optional. Motorized version and digital read out are also available.
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Optical Manufacture
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In order to ensure the continuous improvement in optical quality,
Orion Optics has invested heavily over the years in specialist polishing
machines, high reflectivity coatings and precision testing equipment.
The company's most recent acquisition is a GPI Zygo Laser Inferometer.
Zygo inferometers are one of the world's leaders in laser testing
technology and Orion Optics has deployed the MKIV model which enabled the
company to improve its quality significantly, and to assist in polishing
techniques and aid the design processes too.
The latest GPI series of inferometers will allow Orion Optics to test and
identify errors so small as to be virtually beyond recognition by anything
other than an electron microscope, just a few atoms in size. To achieve the
accuracies needed for consistent quality levels, there is no substitute for
inferometry. Nothing even comes close to the accuracies which can be achieved
by including instruments as the Zygo GPI in an optical testing laboratory.
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A Zygo GPI report is issued to customers purchasing the higher grade optics
featured in the higher specification telescopes.
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Specification
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| Model |
Orion Optics OMC300 |
| Optical Design |
Sub Aperature Maksutov Cassegrain |
| Effective Aperature |
300mm |
| Focal Length (Focal Ratio) |
2700mm (f/9) |
| Primary Mirror |
Guaranteed 1/4 PV wavefront optics and Hilux coatings (1/6 PV option). |
| Optical Resolution |
Diffraction limited for 10mm field, maximum of 40 micron spot size at 20mm field. |
| Secondary Mirror Obstruction |
31% |
| Focuser |
2" Crayford focuser (JMI Precision 2" Crayford focuser option). |
| Tube Weight |
13kgm, 29lbs |
| Finder Scope |
50mm Finder |
| Cooling |
Open, air cooled cell for rapid cooling. Rotatable vent cooled for easy covering
when ambient temperature achieved.
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| Mount Options |
Sky-Watcher PRO or Vixen ATLUX |
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Inferometer Reports (for illustration only, not related to this specific telescope)
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In order to assist customers and prospective customers in understanding
a typical Zygo GPI report, Orion Optics has put together descriptions of
the main displayed features of the reports. Many other features are
available but, due to a limited amount of space, they have decided on
the current display.
Before going into further detail it is important to know what parameters
are used in testing the optics.
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When testing paraboloids they test at the radius of curvature. This ensures
that no astigmatism can be introduced into the optical path. This is a problem
sometimes encountered when testing a paraboloid on a double pass set up with a
perforated flat either the same size or larger than the mirror under test.
Astigmatism is often introduced with this set up due to misalignment of the
optical components and incredible care has to be taken in correct alignment.
It is totally incorrect in this set up to remove astigmatism from the results
electronically on the assumption that all the measured astigmatism is in the
misalignment and not the mirror under test. Doing this falsifies the test as it
also removes all the astigmatism from the test mirror, giving an incorrect
reading.
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To test a mirror on a Zygo there is a need to slightly tilt the mirror to
see fringes which are measured and also the mirror has to be perfectly focused
(power). Flat surfaces are tested in a similar way but with different aspects of
the test removed. Here are the features we remove to achieve a correctly
designed test;
- Paraboloids, spheres and telescopes: Piston, Tilt, Power and Coma are removed
- Flats: Piston and Tilt only are removed only.
Orion Optics will discuss any aspect of its GPI Zygo and its capabilities however,
they cannot, due to technical development procedures, discuss the actual optical set
up of the testing methods they use which were developed in conjunction with Zygo
and the National Physical Laboratory in London.
A sample of a typical report layout is show below (not related to OMC):
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Orion Optics' typical inferometer report (for illustration, not related to this telescope).
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Windows In Report
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Before explaining the 'windows' on the report a word first about scaling.
when an optic is being tested the Zygo's optics are zoomed to have the majority
of the test area filled with the optic under test. This amount of zoom is not
important however, it does show as if two identical optics being tested are not
the same size due to the number of pixels being used in the display. The zoom
factor on two identical optics can range from about 1mm per pixel down to 3mm
per pixel. On average, 1mm per pixel is about normal.
There is no definitive scale of mm-pixels due to this variable and arbitrary
zoom feature. Keeping the zoom level to a scale where the optic fills the
'window' ensures a more realistic RMS value is achieved due to the highest
possible resolution being applied by the Zygo's camera.
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Measurement Controls. This window shows the customers name, the optic type, the optic's identifying
number and the Zygo's wavelength.
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Profile Plot. This plot displays the section of the mirror across
the section shown in the window below it. The section has a small triangle
on each end of the section line. This can be drawn anywhere if needed and
is extremely useful to the optician when studying where small areas of the
mirror need to be worked to achieve specification. The scale of the
irregularities is shown on the left hand edge of the plot. This plot is
also automatically scaled to suit the PV errors, as such, a very good PV
mirror will show very small errors here and tend to look a little rough.
Mirrors of the highest quality show quite rough plots here but,
the actual size of the errors are incredibly small but magnified due to
the auto scaling.
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Oblique Plot. The wavefront of the mirror as seen from an angle
showing a 3D picture of the wavefront errors. Here again, the better the
mirror, the smaller the scale but the very small amount of roughness is
magnified. The maximum and minimum PV values are shown on the right
hand vertical axis of the plot.
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Plan View. This shows the 3D plot as viewed directly from above.
The red colours show the high areas and the blue areas, the low sections.
A valuable tool for the optician who can immediately see what areas are
involved in the overall PV of the wavefront. From this plot he can choose
very accurately which areas (red) need further hand work to achieve a
better PV overall.
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Synthetic Fringes. When a mirror passes through its final test on
the Zygo, it is measured often over a hundred times and often 1024 times,
the Zygo computer averages all the readings to arrive at its final values.
It then transfers the data gathered from typically 30,000 plotted points
and produces a set of fringes from the data. These fringes are the result
of up to 1024 measurements of around 30,000 points and as such give a very
accurate representation of the wavefront under analysis. Any turbulence or
vibration is almost totally removed in this averaging process.
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Data under the Synthetic fringes.
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Time: The time when the test was carried out.
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Strehl: The Strehl value of the optic. On paraboloids we
electronically remove the central section of the mirror on final test, having
first tested it in full aperture with no central section removed. This is to
simulate the mirror in use in an actual telescope. The size of the 'obstruction'
is the typical size of the secondary mirror in the telescope in use. In the
example above, the customer requested a minimum sized flat to achieve maximum
optical performance in visual use.
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P.V. wavefront: The PV wavefront of the optic under test.
The example above shows a wavefront error of slightly better than lambda/6
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RMS: The root mean square of the errors on the wavefront. A
more paractical figure than PV wavefront as it is a measurement of the whole
surface errors and is not just a measure of the highest and lowest points as in
PV.
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AstMag: This figure shows the amount of astigmatism present
in the mirrors wavefront.
For more information on the Zygo set ups for optical testing can be found at
Zygo's web site.
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Notice
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We are constantly checking the accuracy of the technical data. We are prepared
to provide more detailed information on request. Technical data is subject to
change without notice.
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