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Opticstar ARC152 QUAD Optical Tube Assembly (OTA)
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Quality Refractor Astrograph - Flat Filed of View
To order this item outside mainland Britain or Highlands, please contact us.
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Opticstar ARC152 QUAD Optical Tube Assembly (OTA).
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- 152mm Refractor Quadruplet
- Corrected Flat Field
- Focal length: 760mm
- Focal ratio: F/5
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- 8x50mm Finder scope
- Mounting tube rings and dovetail bar
- 25mm Plossl eyepiece (1.25")
- Star Diagonal (1.25")
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Opticstar ARC152 QUAD Optical Tube Assembly (OTA)
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Outline
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The Opticstar ARC-152 QUAD is fast 152mm aperture F/5 achromatic photo-visual refractor. The ARC-152 QUAD
is ideal for both visual and imaging work.
The ARC-152 QUAD incorporates four lenses in two groups of two, Low-Dispersion (LD) Crown/Flint glass is
used and lenses are broadband fully anti-reflection coated for increased contrast and sharpness. The design
uses a F/10 doublet in combination with two additional near full aperture optical elements situated further
down the optical path; these decrease the focal ratio to F/5 and also flatten the field offering very good
off-axis performance.
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Optical Design
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The increased number of lens elements results to better correction of aberrations including coma and sphero-chromatism.
This provides very good correction at F/4.9 and a wide field of view that makes the ARC-152 QUAD very well suited for
wide field astro-imaging due to its fast focal ratio, flat field, higher contrast and markedly reduced false colour
at F/4.9. In effect the secondary spectrum is reduced by nearly a 1/3 and allows a faster relative speed for the same
degree of colour error. The telescope is also well suited for observation readily outperforming 2-element achromats of
the same or similar focal ratios.
The lack of a central obstruction helps to increase image contrast and sharpness when compared to obstructed telescope
designs including Newtonian reflectors, Maksutovs, and SCT telescopes among others. In general the obstruction means that
all incoming light will reach the camera/eyepiece. In addition an un-obstructed optical instrument will reveal significantly
more detail on brighter objects including planets, the Moon and the Sun when compared to obstructed designs. In practice
the obstruction causes a significant loss in contrast and image sharpness.
The obstruction would not be of real concern if the diameter of the obstruction was less than around 10% the telescope
aperture (diameter). It does however become a concern when the obstruction exceeds 20% of the diameter of the aperture;
the vast majority of modern F/10 SCT's for example have obstructions between 35%-40% in diameter. A 35%-40% obstruction
would also translate to a 12%-24% light loss in such cases.
Also at an aperture of under 7-inches atmospheric turbulence has a limited effect unlike apertures of 8-inches and above.
This is important during long exposures and mostly when imaging deep sky objects.
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Opticstar ARC152 QUAD.
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Imaging
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The ARC-152 QUAD offers a fitting solution when imaging even under not ideal conditions since the
scope offers everything the imager would need in such cases i.e. good aperture, flat imaging field,
fast focal ratio, reduced false colour at F/5 and no obstruction.
Most important the ARC-152 QUAD would be ideal for narrow band imaging with any size sensor and without
the need for a flattener when considering that false colour would no longer be an issue. For the same
reasons and in conjunction with a short focal length the ARC-152 QUAD is ideal for imaging or viewing
the Sun in H-alpha with an appropriate filter.
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Imaging and Viewing the Sun
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Being a flat-field, air-spaced refractor with metal knife edge baffles the ARC-152 QUAD is also ideal for imaging
and viewing the Sun when used with a specialist (H—alpha) Solar filter at the eyepiece end and in conjunction with
a full aperture Solar heat rejection filter that is required due to the large size of the telescope’s objective
lens and optical design.
Please note that suppliers of specialist, at the eyepiece, H-alpha filters recommend that the telescope’s aperture
should not exceed a given size and/or a full aperture heat rejection filter should also be used in conjunction with
a particular H-alpha eyepiece. Please contact the supplier of such equipment for advice.
Otherwise refractor telescopes with cemented or oil spaced objectives are not recommended for Solar work unless
they are always used with a full aperture Solar filter. Newtonian and catadioptric designs in general are also
not suited for use with specialist H-alpha eyepieces alone as the heat from the Sun will have an adverse effect
on the small secondary mirror over time unless a full aperture Solar filter is used. White light full aperture
Solar filters are inefficient in such cases as they also proportionally reduce the amount of H-alpha entering
the telescope and reaching the H-alpha eyepiece.
Finally make certain that the Solar Filter you intend to use is safe, never use cheap eyepiece type Solar filters
as they can crack under the heat and seriously damage your eyes.
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Field of View
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The ARC-152 QUAD is relatively portable due to its shorter focal length which in turn offers unusually
wide fields of view for the aperture.
For example the ARC-152 F/5 QUAD will show a 4.2 degrees field of view with an Opticstar XS 38mm 70 degrees
AFOV (apparent field of view) eyepiece. This will easily fit in the field of view particularly large objects
like the Andromeda Galaxy. Eyepieces with larger AFOV will offer even wider fields of view.
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Construction
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A high quality optical tube keeps the optics precisely aligned allowing for heavier optical equipment to be
attached at the focuser end. The optical tube greatly benefits from anti-reflection coatings and knife-edge
baffles that prevent stray light from reaching the focal plane thus increasing image contrast and sharpness
further. The optical tube assembly has a dew shield that also protects the lenses from condensation forming
on the objective when the telescope is used in unfavourable conditions.
The focuser's 2" rack & pinion focuser draw tube has an etched millimetre scale to aid with focusing and
repositioning, in addition the focuser has brass compression rings to securely support and not scratch accessories.
It comes with a 1.25" eyepiece adapter so it will accommodate both 2" and 1.25" eyepieces and other accessories.
A single–piece cradle with a carry-handle is used to lift and support the telescope on its mount. The telescope
has a Vixen/Skywatcher type dovetail and will mount on most astronomical mounts including the Opticstar EQ1300 GOTO.
The carry-handle has been designed so as to enable the user to attach a DSLR, guide-scope or other accessories
without the need of side by side platforms or similar, thus reducing costs, the total weight and the need for a
heavier mount.
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Collimation
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The ARC-152 QUAD comes collimated from the factory. If there was a need the objective could be collimated by an
experienced user, three sets of easily accessible screws allow for precise collimation. Collimation can take
place on a star under good atmospheric conditions or with the use of an artificial star like the
Opticstar Artificial Star XL.
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Accessories
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The ARC-152 QUAD comes with a 8x50mm finder scope and bracket. A 1.25" diagonal, and 25mm Plossl eyepieces
are also included. An optional 13% transparency Moon filter is recommended as is a 2.5mm-3mm eyepiece
for high power viewing.
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Bundled accessories.
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Specification
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| Model |
Opticstar ARC152 QUAD |
| Aperture |
152mm |
| Focal ratio |
F/5 |
| Focal length |
760mm |
| Objective |
4 achromatic lenses in two groups of 2, can be collimated |
| Optical coatings |
Anti-reflection coated |
| Optical tube |
Internally anti-reflection coated with metal knife-edge baffles |
| Dew shield |
Yes |
| Finderscope saddle |
Yes |
| Focuser type |
Rack & Pinion with lock |
| Focuser |
2" with 1.25" adapter (T-threaded for camera use) |
| Tube rings |
Dual rings with carrying handle and dovetail platform |
| Tube weight |
10.3kg (inc. rings) |
| Tube length |
1110mm |
| Eyepieces |
Plossl 1.25" 25mm |
| Magnification |
With bundled eyepiece:
With optional eyepieces and barlow lenses:
- w/15mm eyepiece x50;
- w/10mm eyepiece x76;
- w/10mm eyepiece and x3 barlow lens x228;
- w/9mm eyepiece and x3 barlow lens x253; (maximum practical magnification)
- w/15mm eyepiece and x5 barlow lens x253; (maximum practical magnification)
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| Star diagonal |
1.25"; 90° |
| Finderscope |
8x50mm with bracket |
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Opticstar ARC Series Refractor Optical Tube Assemblies
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Opticstar ARC Series Refractor Optical Tube Assemblies
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Opticstar ARC QUAD Series Astrograph Refractor Optical Tube Assemblies
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Opticstar ARC QUAD Series Astrograph Refractor Optical Tube Assemblies
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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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