Opticstar ARC-152 QUAD User manual

© Opticstar Ltd 20141
WARNING!
DO NOT USE THE TELESCOPE TO LOOK AT THE SUN!
Do not disassemble your telescope, there are no user
serviceable parts inside. Disassembling the lens cell will
invalidate your warranty.
Opticstar Ltd
87 Washway Road, Sale, Greater Manchester M33 7TQ United Kingdom
WEB: www.opticstar.com - EMAIL: [email protected]
LOOKING AT OR CLOSE TO THE SUN WITH A
TELESCOPE OR FINDERSCOPE WILL CAUSE INSTANT
AND PERMANENT DAMAGE TO YOUR EYES. CHILDREN
SHOULD AT ALL TIMES BE SUPERVISED BY A
RESPONSIBLE ADULT WHILE OBSERVING.

© Opticstar Ltd 20142
Introduction
Congratulations on the purchase of your Opticstar ARC-152 achromatic refractor. TheARC-152 telescope is very
well suited for astronomical observation. Its fully coated achromatic optics, solid construction, metal knife-edge
baffles and long focal length make it ideal for high power viewing in general and for the Moon,planets and Sun in
particular (with an appropriate Solar filter).
Please read through the manual to familiarise yourself with thetelescope so that you can get the most out of the
equipment. This manual details the setting up, operation, specificationand optional accessories of the Opticstar
ARC-152 telescope.
Parts
The Opticstar ARC-152 telescope package consists of the following:
1. Optical Tube with rings and dovetail.
2. Finder scope with Bracket
3. 1.25” Star Diagonal
4. 25mm Plossl eyepiece
5. This Manual
Mounting the Telescope
The telescope is fitted with a Vixen type dovetail platform and will mount on most telescope mounts including the
Opticstar EQ700 and Opticstar EQ1300 GT computerised mount.
The telescope can be mounted as is on an extra heavy duty photographic tripod with a heavy photographic thread.
Heavy heads will work adequately at low magnifications, an extra heavy duty geared head with slow-motion
controls is required for higher magnifications or when fine control is required.
Finder-scope Assembly and Alignment
To assemble the finder-scope place the finder-scope optical tube
in the supplied bracket and lightly tighten the six thumbscrews
enough to secure the finder-scope optical tube in place as in the
picture on the right. Please note that two of the six thumb
screws are spring loaded. Once you set the spring loaded screws
to the desired position you would only need to adjust the four
remaining thumb screws to align the finder scope as outlined in
the following page.
Once Mount the assembled finder-scope to the telescope and
secure it in place. Attach the telescope to a mount/tripod.
The finder scope has been focused at infinity at the factory. If there was a need to refocus the finder scope you can
do so as follows:
1. Dismount the finder scope form the telescope and remove it
from its bracket.
2. Release the Locking Ring by turning it several times.
3. Point the finder scope to your target i.e. star at ‘infinity’.
4. Turn the Objective Cell to bring the star in sharp focus.
5. Secure the Objective Cell position by tightening the Locking
Ring against it.
6. Re-assemble and mount the finder scope to the telescope.
Locking Ring
Objective Cell

© Opticstar Ltd 20143
To align the finder-scope perform steps 1 through 9 as outlined below, we recommend that the telescope is first
aligned during daytime. Please note that the view would appear mirrored and/or flipped depending on your
arrangement.
1. Attach the finder-scope to the telescope.
2. Mount the telescope to a photographic tripod or astronomical mount.
3. Attach the supplied 1.25” astronomical diagonal to the telescope and secure it in place.
4. Place a low power (i.e. 25mm) eyepiece in the telescope’s diagonal, secure it in place.
5. Loosen the movement locks of your mount/tripod, this will allow the telescope to move freely.
6. Point the telescope to a distant land object a few miles away (i.e. the top of a lamp post, tree or chimney).
You will notice that the image will be mirrored and/or upside down, this is normal for an astronomical
telescope.
7. Turn the focuser knob to bring the target in focus and centre the object in the eyepiece.
8. Re-tighten the tripod/mount movement locks so that the telescope remains stable during the finder-scope
alignment procedure.
9. Look through the finder-scope.
10. Use the collimating thumb-screws on the finder-scope’s bracket to align the finder-scope so that the cross-
hair is precisely over the same object in the eyepiece. You only need to use the three thumb-screws on a
single ring to align the finder-scope.
The finder-scope is now aligned to the main telescope. You can check and refine alignment on a night sky object
like a star if required. Please note that the view will not be the right way up and views will differ depending
whether a diagonal is used or not. If you do not use a diagonal you may need an extension tube to reach focus.
Using the ARC-152
If you are new to observing it is advisable to first use the telescope during daytime to learn how it operates. First
mount the telescope on a tripod or telescope mount. Once the optical tube has been mounted attach the finder-
scope, then attach a diagonal and low power eyepiece i.e. 25mm. Make certain that all parts are secure.
Simply choose a distant target to observe like a large building or large tree. Point the telescope towards the target
so that it roughly lines up with the target.
Look through the finder-scope, if you have not aligned it already this is a good time to do so before you proceed.
Move the telescope until the target is visible in the finder-scope and positioned under the cross-hair.
Once the object is lined up in the finder-scope you will be able to observe the target through the telescope’s
eyepiece. Look through the eyepiece, turn the focuser knob to bring the target into focus.
Terrestrial Observation
You can use the telescope for terrestrial observation for which you need a prism diagonal, otherwise the image will
appear mirrored and/or upside down. In astronomy it is not relevant if the Moon is say upside down, what is
important is to capture as much light as possible and correctors take some of this valuable light away.
Please note that this is a heavy and large telescope and as such it is difficult manage on a tripod. As such we
recommend that heaviest duty tripods and tripod heads.
Telescope view
Finder
-
scope view,
not aligned
Finder
-
scope view,
aligned

© Opticstar Ltd 20144
Astronomical Observation
When observing at night your first target should be the Moon as it offers a wealth of detail;it is large, bright and
easy to locate. Spend some time with the Moon, high magnifications will show many interesting features. You will
see mountain ranges, craters and evidence of volcanic activity when the Moon was mainly composed of melted
rock. You will need a neutral density filter to observe the Moon, a 13% transparency filter is recommended.
Once confident with the Moon the planets would be the next target. Planets are easy to identify as they are bright
and do not twinkle unlike stars. Please note that when a planet is out of focus and it becomes very dim you may not
be able to see it.
Use the finder-scope to place the planet in the centre of the field of view, then look through the eyepiece and use
the telescope focuser to bring the planet into focus. Planets that are easy to observe include Venus, Mars, Jupiter
and Saturn. You will get the most out of the planets at higher magnifications.
At high magnifications planets will look like marbles and will reveal a high degree of detail to the trained eye.
Jupiter will show banding,the Red Spot and you will also be able to observe the Galilean Moons.
Saturn is probably the most exciting planet to observe through a telescope. While surface detail is subtle its rings
are a unique site and you should be able to observe the Cassini division which appears as a black gap between the
rings.
Mars also known as the Red planet will reveal a good amount of detail when close to Earth. Its orange colour is
prominent and surface markings are visible as are the Polar caps when present.
Venus can be observed early in the morning before dawn or just after sunset. Venus appears quite large in the
telescope but its atmosphere will hide any surface detail.
Deep sky observation greatly depends on the prevailing sky conditions. City lights, low sky transparency and the
presence of the Moon will greatly affect what you can see through the telescope. From a dark site and under
favourable conditions you will be able to see several deep sky objects including star-clusters, galaxies, nebulae and
comets. Such objects with the exception of stars will appear as feint clouds of matter in monochrome, human eyes
are not able to pick up colour. Cameras on the other hand can reveal colour and considerable amounts of detail.
Good deep sky objects to look for at the very beginning include the Orion Nebula, the Trifid nebula, the Ring
nebula, the Andromeda Galaxy and a number of star-clusters among various other objects.
Observation Skills
In general it is easier to locate a target with a low power eyepiece i.e. 25mm. Once the target has been located
centre it in the field of view before replacing the 25mm eyepiece with a high power one, i.e. 5mm (x240).
There are many factors that will affect the quality of the image through the eyepiece; such factors include sky
quality in terms of the level or light pollution, sky transparency and the presence of the Moon if you are observing
deep sky objects like galaxies and nebulae. If you use an equatorial mount make certain that the telescope has been
balanced and that all screws are reasonably tight.
You will always be limited by the type, size and the optics of your telescope in what you can see. However there
are other important factors to consider that can substantially improve the experience. Let the optics to cool down
for best results, this varies depending on the size and type of the telescope but typically a 152mm refractor like the
ARC-152 will need around 15 minutes to cool down.
Please keep in mind that targets near the horizon will not look as sharp, targets near the zenith will look
substantially sharper. Avoid setting your telescope on concrete; wood and grass are better as they do not release
heat. Your line of sight should ideally not pass just over a warm house; the rising heat will substantially affect the
quality of the image.
The long focal length of the ARC-152 scope makes it ideal for planetary and Lunar viewing.When conditions are
not favourable the maximum useful magnification for most scopes will be around 25-35 times per inch of aperture.
Otherwise expect higher practical magnifications per inch of aperture under favourable conditions with good
quality eyepieces.

© Opticstar Ltd 20145
Dew shields are useful as they cut stray light entering the telescope, they also protect objective lenses from dew
building up on the optics and also increase contrast. The ARC-152 comes with built-in dew-shield.
Observing the Sun
Special precautions need to be taken when observing the Sun with a telescope. A full aperture Solar filter must be
used to dramatically reduce the amount of light that enters the telescope, only use filters designed to be used for
Solar observation with a telescope. A second filter can also be used at the eyepiece end in conjunction with a full
aperture Solar filter to increase the level of surface detail i.e. Solar Continuum Filters. Such filters work very well
with digital cameras in particular and will reveal additional detail otherwise not visible to the human eye. Always
check the integrity of any Solar filter before using it with a telescope. A hair-line scratch on a filter is enough to
damage your eyesight. If in doubt seek professional advice and never point a telescope towards the Sun without a
suitable Solar filter.
Visual Accessories
Depending on what came with your telescope you may need a number of extra eyepieces which will provide a
wider range of magnifications. For example high magnifications are required for the Moon, planets and planetary
nebulae. Low magnifications are useful for observing extended objects and for locating targets. Ninety degrees star
diagonals are necessary as they make astronomical observation comfortable. For terrestrial observation 45o
degrees prism diagonals are preferred, such diagonals will also offer a corrected view unlike star diagonals.
A 13% transparency Moon filter will be necessary to observe the Moon with almost all medium to large sized
telescopes including the ARC-152, light pollution filters can also help by reducing sky glow and incoming light
from other local light sources. Finally a 4mm-4.5mm eyepiece is highly recommended for high power viewing of
the Moon and planets.
These telescopes can perform well and as such they will benefit from quality optical accessories including the
Opticstar XL range of premium tele-extenders, Zoom and prime eyepieces as well as the more affordable range of
Opticstar XS eyepieces.
Optics Care
Lenses can be treated as camera lenses for cleaning purposes. What makes them difficult to clean is the large size
of such optical elements. The general rule is not to touch the optics and only clean them when absolutely necessary,
dust on the objective lens could be removed with very gentle strokes of a camel hair brush or with an optics
cleaning cloth available at camera shops.
You can remove condensation from the optics with a hair-dryer set to ‘cold’. Otherwise bring the telescope inside
and let condensation to dissipate before putting on the cover. Place the telescope on a table and not on the floor
where most of the dust can be found. Never try to remove condensation using a cleaning cloth or similar, this will
most likely smear the optics.
Optics Collimation
The telescope 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 high up in the sky and under very good atmospheric conditions. Alternatively the telescope can be collimated
or with the aid of an artificial star like the Opticstar Artificial Star XL

© Opticstar Ltd 20146
APPENDIX A
Appendix A outlines the most important aspects of a telescope in terms of its focal length and focal ratio. These
values are important as they dictate magnification, exposure times when imaging and fields of view.
Practical Magnification
The focal length of a telescope can be calculated by multiplying the focal ratio of the telescope with its aperture i.e.
an f9.5 refractor with 152mm of aperture will have a focal length of approximately 1,200mm (7.9x152=1,206).
In a telescope, magnification is the number of times an object appears larger to the observer when compared to
what the observer can see with the naked eye. There is no real limit to the amount of magnification possible in a
telescope, but practical magnification is limited by the optical system and is normally around 30-40 times per inch,
and around 50-70 times per inch of aperture for high quality apo-chromatic refractors. Experienced observers using
high quality telescopes may push these figures even higher under favourable conditions.
Please keep in mind that the maximum useful magnification from a suburban yard using any telescope will be
around x30 – x35 per inch of aperture for most of the time, this is due to light pollution (sodium lights in
particular), thermal currents and other environmental factors. Expect higher magnification from dark sites and
when transparency is good.
Eyepieces and Magnification
The actual magnification capability of a telescope will vary depending on the eyepiece attached to the telescope.
Magnification can be changed by simply exchanging eyepieces.
Magnification depends on two factors. The focal length of the telescope and the focal length of the eyepiece used.
To calculate the magnifying power an eyepiece gives, simply divide the focal length of the eyepiece into the focal
length of the telescope.
Magnification = telescope’s focal length / eyepiece’s focal length = F/f
For example a telescope with a focal length of 1,200mm and an eyepiece with a focal length of 10mm will magnify
its target 120 times (1,200/10=120).
Barlow lenses can be employed in conjunction with an eyepiece to increase magnification. To calculate the
magnifying power an eyepiece gives in conjunction with a Barlow lens, simply divide the focal length of the
eyepiece into the focal length of the telescope and multiply the result by the Barlow’s magnifying power.
Magnification = telescope’s focal length / eyepiece’s focal length x Barlow power
For example a telescope with a focal length of 1,200mm used with an 10mm eyepiece and x2 Barlow will offer a
magnification of x240 (1,200/10x2=240).
Focal Ratio
The focal ratio represents the speed of the telescope’s optics, the focal ratio can be calculated by dividing the focal
length by the telescope’s aperture.
Telescopes with faster/shorter focal ratios benefit from wider fields of view, and a subsequent increase in
brightness and image resolution. Fast f/4-f5 focal ratios are generally best for lower power wide field observing and
deep space imaging. On the other hand slow f/10 focal ratios and above are better suited to higher power Lunar and
planetary observation as well as high magnification imaging in general.
O
f
F
FOCUSER
FOCUSER
DRAWTUBE
OBJECTIVE LENS
EYEPIECE
INCOMING LIGHT

© Opticstar Ltd 20147
For example when imaging extended deep sky objects like nebulae and galaxies an f/4 telescope will capture four
times the amount of light in the same time period when compared to a telescope with an f/8 focal ratio. The same
does not apply to single point light sources like stars where aperture alone dictates what you can see.
Field Of View
The field of view is the portion of the sky that is visible through the telescope and depends on the focal ratio of the
telescope. In general higher magnifications result in smaller fields of view.
Short focal ratios (f/4) with wide fields of view greatly favour deep sky viewing and imaging, where focal ratios of
f/10 and above are better suited for planetary and Lunar observation. Focal ratios in between these values (f6) may
be considered appropriate for general use.
It is possible to calculate the field of view of a telescope given a certain eyepiece using the following formula.
Actual Field of View = Eyepiece Apparent Field of View / Magnification
where Magnification = Telescope Focal Length / Eyepiece Focal Length
Consider a telescope with a 1,200mm focal length and a 10mm eyepiece with a 50 degrees Apparent Field of View.
Magnification = 1,200 / 10 = 120 ~Actual Field of View = 50 / 120 = 0.42 degrees
APPENDIX B
Opticstar ARC-152 Specification
Aperture 152mm
Focal ratio F7.9
Focal length 1,200mm
Objective Achromatic doublet, can be collimated
Optical coatings Fully anti-reflection coated
Optical tube Internally anti-reflection coated with metal knife-edge baffles
Dew shield Yes
Finder-scope saddle Yes
Focusertype 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 10.45Kg (inc. rings)
Tube length 1.270mm
Eyepieces 25mm Plossl
Star Diagonal 90o1.25”
Finder scope 9x50 (with bracket)

© Opticstar Ltd 20148
WARNING!
DO NOT USE THE TELESCOPE TO LOOK AT THE SUN!
Opticstar Ltd
87 Washway Road, Sale
Greater Manchester
M33 7TQ
United Kingdom
WEB: www.opticstar.com - EMAIL: [email protected]