The designers of the Air Spaced Triplet ED Apo …...primary mirror, large 203mm aperture, corrected...

© Opticstar Ltd 2014 1

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]

AVOID TOUCHING THE PRIMARY OF SECONDARY MIRRORS SURFACES AS THEY ARE DELICATE.

DO NOT DISASSEMBLE THE TELESCOPE. THERE ARE NO USER SERVICEABLE PARTS INSIDE. DISASSEMBLING THE TELESCOPE WILL INVALIDATE YOUR WARRANTY.

LOOKING AT OR CLOSE TO THE SUN WITH A TELESCOPE OR FINDER-SCOPE WILL CAUSE INSTANT AND PERMANENT DAMAGE TO YOUR EYES. ALWAYS USE THE APPROPRIATE PROTECTION WHEN OBSERVING OR IMAGING THE SUN. CHILDREN SHOULD AT ALL TIMES BE SUPERVISED BY A RESPONSIBLE ADULT WHILE OBSERVING.

THIS IS A FRAGILE, HEAVY AND BULKY TELESCOPE. ONLY CARRY WHAT YOU CAN EASILY HOLD, AND ASK FOR HELP IF IN DOUBT.

BE AWARE THAT JEWELLERY CAN CAUSE DAMAGE, INCLUDING LONG NECKLACES, AND LOOSE BRACELETS.

TO AVOID DANGER OF SUFFOCATION, KEEP PLASTIC BAGS AND WRAPPINGS AWAY FROM BABIES AND CHILDREN.


14. Focusing knob

15. Focuser drawtube

16. Fine control focusing knob

17. 2”/1.25” accessory adapter

18. Focuser locking screw

19. Focuser tension screw

14 15

16

17

18 19

1

2

3

4

5

6

7

8

8

9

10

11

12

13

13

1. Optical Tube Assembly (OTA)

2. Dovetail

3. Quick release tube rings

4. Optical tube handle

5. Finder-scope

6. Finder-scope bracket and support

7. Finder-scope shoe

8. Finder-scope adjustment screws

9. Finder-scope LED illuminator

10. Dual speed focuser

11. Optical corrector (optional)

12. Secondary mirror precision

collimation system

13. Retaining screws for secondary

mirror supports


Introduction Congratulations on the purchase of your Opticstar ARX-200 astrograph. The ARX-200 has been designed

primarily for astronomical imaging and can also be used for astronomical observation. Its very fast F3.9 focal ratio

primary mirror, large 203mm aperture, corrected optics and carbon-fibre tube make it ideal for imaging deep sky

objects while providing wide fields of view for such a large aperture.

Please read through the manual to familiarise yourself with the ARX-200 so that you can get the most out of the

equipment. This manual details the setting up, operation, specification and optional accessories of the Opticstar

ARX-200.

Parts The Opticstar ARX-200 telescope package consists of the following:

1. Optical Tube with rings and dovetail

2. Finder-scope with Bracket

3. 4-element, 2” field flattener/corrector specifically designed for the ARX-200

(included with ARX-200 Astrograph model only)

4. 25mm Plossl eyepiece

5. Case

6. This Manual

Mounting the Telescope The ARX-200 is fitted with a Vixen/Skywatcher type dovetail platform and will mount on most telescope mounts

like the Opticstar EQ1300 GT computerised mount.

The telescope could be mounted on an extra heavy duty tripod with an appropriate slow motion head. Heavy duty

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 non-spring loaded

thumb screws to the desired position you would only need to

adjust the two remaining spring-loaded thumb screws to align

the finder-scope, the procedure is outlined in the next page.

Now 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 from the telescope and remove it

from its bracket.

2. Release the Locking Ring by turning it several times.

3. Point the finder-scope to a distant 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


Finder-scope Illuminator The ARX-200 finder-scope uses a red LED variable illuminator

to light up the crosshair. You can adjust the brightness of the

built-in LED by turning the brightness-adjustment-knob on top

of the illuminator.

Always remember to switch off the illuminator to save on

batteries at the end of a session. You can switch off the

illuminator by turning the brightness-adjustment-knob clockwise

until the LED goes off, this will be confirmed by an audible

click. The illuminator requires two 1.5V LR41 batteries to

operate. These can typically be found at camera shops and

electronics suppliers.

To align the finder-scope perform steps 1 through 9 as outlined below, we recommend that the telescope is first

aligned during daytime. Take care not to point the telescope or finder-scope towards the Sun. 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.

3. Place a low power (i.e. 25mm) eyepiece in the telescope’s diagonal, secure it in place.

4. Loosen the movement locks of your mount if applicable, this will allow the telescope to move freely.

5. 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 upside down, this is normal for an astronomical

telescope.

6. Turn the focuser knob to bring the target in focus, then centre the object in the eyepiece.

7. Re-tighten the tripod/mount movement locks if applicable so that the telescope remains stable during the

finder-scope alignment procedure.

8. Look through the finder-scope.

9. 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. In practice you would 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.

ARX-200 Corrector It is recommended that the ARX-200 is used with the ARX-200 corrector fitted. Please note that the ARX-200

focuser will accept an extension tube that in some cases would need to be in place for the telescope to reach focus

depending on the camera or whether an eyepiece is used.

Using the ARX-200 If you are new to observing it is advisable to first use the telescope during daytime to learn how it operates. Make

certain that you do not point the telescope or finder-scope towards the Sun. First mount the telescope on a telescope

mount. Once the optical tube has been mounted attach the finder-scope, then attach a low power eyepiece i.e.

25mm. Make certain that all parts are secure.

brightness adjustment knob

Telescope

view

Finder-scope view, not aligned

Finder-scope view,

aligned


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 the finder-scope

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.

The ARX-200 like all reflector telescopes of this design are not well suited for terrestrial observation due to the

position of the eyepiece and image orientation.

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 it becomes very dim

and 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 high magnifications

typically using a 2.5mm – 3.5mm eyepiece.

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, in general

human eyes are not able to register 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 medium power one, i.e. 5mm (x156).

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 203mm reflector like the

ARX-200 will need around 30 minutes to cool down.

Image by John Haunton (AU)


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 as much 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 short focal length of the ARX-200 makes it ideal for wide angle observation and imaging. 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.

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 ARX-200 would benefit from a short dew shield,

especially when imaging from the city suburbs.

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 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 accessories 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.

A 13% transparency Moon filter will be necessary to observe the Moon with almost all medium to large sized

telescopes including the ARX-200, light pollution filters can also help by reducing sky glow and incoming light

from other local light sources. Finally, a 2.5mm – 3.5mm eyepiece is generally 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 Eyepieces can be treated as camera lenses for cleaning purposes. The general rule is not to touch the optics and

only clean them when absolutely necessary, dust on a lens could be removed with very gentle strokes of a camel

hair brush or very gently 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 or

eyepieces indoors and let condensation to dissipate before putting on the cover. Place the telescope or eyepiece 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. When dealing with mirrors we recommend that you have

these cleaned professionally and always seek advice if you are not certain. Mirror surfaces are delicate and should

not be simply wiped with a cloth.

Optics Collimation If there was a need the RX-200 could be collimated by the user, the ARX-200 comes with a

high precision secondary cell with micro-adjusters to make precise collimation a simpler

process. Collimation can take place on a star high up in the sky and under very favourable

conditions. Alternatively, the telescope can be collimated with the aid of an artificial star like

the Opticstar Artificial Star XL.

Image by Gary Palmer (UK)


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 f3.9 reflector with 203mm of aperture will have a focal length of approximately 792mm (3.9x203=791.7).

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 a dark site and

when sky 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 792mm and an eyepiece with a focal length of 10mm will magnify

its target approximately 79 times (792/10=79.2).

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 792mm used with an 10mm eyepiece and x2 Barlow will offer a

magnification of approximately 158 times (792/10*2=158.4).

f

F = f1 + f2

INCOMING

LIGHT

PRIMARY MIRROR

PRIMARY MIRROR

FOCAL POINT

f1 f2

SECONDARY

MIRROR

EYEPIECE


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-f/5 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.

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 (f/6) 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 792mm focal length and a standard 40mm Plossl eyepiece with a 50 degrees Apparent

Field of View.

Magnification = 792 / 40 = 19.8 Actual Field of View = 50 / 79.2 = 2.52 degrees

When using the ARX-200 with say an Opticstar 2” 38mm XS SWA 70 degrees Apparent Field of View eyepiece the Actual Field of View through the eyepiece would be just under 3.6 degrees, this exceptionally wide filed would fit the whole of the Andromeda Galaxy in the field of view.

Camera Sensor Size and Field of View The physical size of the camera sensor and the focal length of your telescope are the two most important factors

when considering the amount of sky you can capture on a particular sensor assuming that there are no other optics

between the telescope objective and the camera sensor that would alter the focal length of the telescope.

The size of the projected image given a certain focal length can be calculated by the following formula.

Projected Image Size (mm) = angular size (arc-seconds) * focal length (mm) / 205,714.0

For example, an object 1800 arc-seconds in diameter like the Moon in a telescope with a focal length of 792mm

like the ARX-200 will project an image of the Moon on the sensor 6.93mm in size/diameter.

1 degree = 60 arc-minutes, 1 arc-minute = 60 arc-seconds, 1 degree = 3600 arc-seconds

The angular size of various deep sky objects can be found in star charts, computer planetarium software

applications and various books. This information is also readily available on the Internet, simply use your favourite

search engine with the name of the object in question and the phrase “angular size”, i.e. M42 angular size.

Please note that barlow lenses and focal reducers can be used to change the focal length of your telescope which in

turn will affect the field of view and size of the projected image on the sensor.

Image by K. (Japan)


APPENDIX B Establishing the Need for Collimation There are two ways to establish whether the ARX-200 needs to be collimated but it is easier to do this indoors

rather than outdoors.

To check collimation in doors all you require is an inexpensive Cheshire/collimation eyepiece. To do so outside

you would need to mount the telescope and observe a star at high magnifications.

Indoors Test To establish whether the telescope is collimated you would need a Cheshire eyepiece. Cheshire eyepieces are

simple, inexpensive devices with no optics that can be used to test and also collimate telescopes such as the ARX-

200. Cheshire eyepieces resemble an eyepiece in shape but with a very small opening (dioptre) used to look down

the telescope’s optical tube. The 2mm diameter dioptre ensures that the observer’s eye remains central which is

required during the collimation process.

Remove the telescope’s front cover and place the Cheshire eyepiece in the focuser

drawtube, secure it in place. Look down the tube through the Cheshire eyepiece and

observe the secondary mirror and reflection of the primary. The telescope is

collimated when the primary, secondary mirrors and their reflections appear

concentric as in the images in this page. If the ‘rings’ appear non concentric the

telescope will require collimation.

More sophisticated Cheshire eyepieces have a cross-hair that indicates the centre of

the focuser’s drawtube. Such eyepieces help with collimation but are not necessary.

In this example the Cheshire eyepiece cross-hair shows in blue. Please note that once

the telescope has been precisely collimated the reflection of the cross hair will not be

visible as it will be obstructed by the actual crosshair.

Down the tube view of collimated telescope through a Cheshire

eyepiece

Cheshire eyepiece dioptre

Primary mirror

Secondary mirror

Actual Secondary mirror holder

Secondary mirror supports reflected on primary mirror

Primary mirror centre indicator ring

Reflection of secondary mirror

CHESHIRE EYEPIECE

Collimated view


Outdoors Test To ascertain that the telescope needs to be collimated you would need to point the telescope to a 2nd or 3rd

magnitude star and carefully observe the star at high magnifications after the telescope had time to cool down. Brighter stars will not work as well, stars higher up in the sky will be better suited. Steady atmospheric conditions

are required.

Collimated

1. Point the telescope to a 2nd or 3rd magnitude star like Polaris.

2. Place the star precisely in the centre of the field of view.

3. Bring the scope in sharp focus using a high power eyepiece i.e. 2mm-2.5mm.

4. Turn the focus-knob counter-clockwise until you see a defocused annulus (fat ring). If the annulus is leaning

on one side the telescope would require collimation.

5. Turn the focus-knob counter-clockwise until you see a defocused annulus (fat ring). If the annulus is leaning

on one side the telescope would require collimation.

To summarise if the rings appear precisely concentric both in focus and out of focus then the telescope is

collimated. If the annulus is leaning on one side then the telescope would require collimation. Please note that observing the pattern through a green filter can help.

Establishing the need for Collimation: The Airy DIsk Method A more sensitive method for identifying very minor collimation issues is by studying the Airy Disk. Very steady

atmospheric conditions, a cooled down telescope and considerable experience are all required if you choose this

method.

To ascertain that your telescope needs to be collimated point the telescope to a 2nd magnitude star like Polaris.

Brighter stars will not work as well, stars higher up in the sky will be better suited. Steady atmospheric conditions

are absolutely necessary in this case.

Wait for until seeing is perfectly steady and aim your telescope to the selected

star. Place the star precisely in the centre of the field of view. Bring the scope in

sharp focus and increase magnification until you reach the maximum limit for

that evening.

Once at the highest power possible and in sharp focus study the focused star

carefully. The Airy Disk that surrounds the star should be circular and

symmetrically lit, in addition the two or more Airy Rings that surround it

should be symmetrical in relation to the Airy Disk. If the Airy Disk and Airy

Rings are concentric and symmetrical then the scope is perfectly collimated.

Note that in general the spacing and brightness of the Airy Rings will vary

depending on the size of the central obstruction.

Also note that the Airy Rings and Disk will not be as readily visible as in the illustration and will appear much

fainter through the eyepiece.

Telescopes with different size obstructions will show different ring patterns all of which need to be symmetrical.

Star in sharp focus

Airy Disk Airy Rings

Star

Collimated Out of Collimation Collimated

Collimated

Star in sharp focus


Collimating the ARX-200 with a Cheshire Eyepiece

Preparing the Secondary for Alignment Remove the telescope’s front cover and place the Cheshire eyepiece in the focuser drawtube, secure it in place.

Follow the instructions below to set the Secondary Mirror Assembly to Home Position:

1. Carefully remove the Central Bolt Cap by turning it anti-clockwise

2. Carefully remove the two Micro Adjustment Caps by turning them anti-

clockwise

3. Loosen the three Central-Bolt Locking Screws by turning them anti-

clockwise several turns

4. Loosen the two Setting Screws by turning them anti-clockwise by around

three turns

5. Adjust the two Micro-Adjustment Knobs so that the Central Bolt is

central within its housing

6. Lightly tighten the two Setting Screws

Please keep in mind that the two Micro-adjustment Knobs will later be used for

the fine alignment of the secondary mirror and once the telescope has already been

roughly collimated as explained below.

Look down the ARX-200 tube through the Cheshire eyepiece and observe the

secondary mirror and reflection of the primary. When the telescope is collimated

all optical elements in the light path will appear concentric as in the image on the

right. Note that you do not need a star or laser to collimate the ARX-200,

these are optional. You are now ready to proceed with collimation

Secondary Mirror Assembly


MICRO ADJUSTMENT

CAP

MICRO ADJUSTMENT KNOBS SETTING SCREWS

SECONDARY MIRROR SUPPORTS

MICRO ADJUSTMENT

CAP

CENTRAL BOLT LOCKING SCREWS

CENTRAL

BOLT CAP

CENTRAL

BOLT

Collimated view


Secondary Mirror Alignment If the secondary mirror appears centred though the Cheshire eyepiece but the

reflection of the primary mirror is off-centre and partially visible you will need to

adjust the secondary mirror assembly.

Slightly loosen the Support Locking Screw so that you can turn the Secondary

Mirror Holder. Use the Knurled Hand-screw to gently turn the Secondary

Mirror Holder until it appears as centred and as round as possible through the

Cheshire eyepiece. Avoid freely rotating the Secondary Mirror Holder or the

Support Bolt as the internal pressure springs could warp. Simply gently turn the

Secondary Mirror Holder a few degrees left or right to precisely face the

telescope focuser.

Now lightly tighten the Support Locking Screw to secure the Secondary Mirror Holder in place.

Loosen the two Setting Screws by turning them anti-clockwise three to four turns. Then use the two Micro-

adjustment Knobs to perform any corrections. Once the Primary Mirror is centred in the Cheshire eyepiece lightly

tighten both Setting Screws.


SECONDARY MIRROR SUPPORTS

CENTRAL BOLT LOCKING SCREWS

MICRO ADJUSTMENT KNOB/S (with cap/s on)

SETTING SCREW/S

KNURLED HAND-SCREW

SECONDARY MIRROR HOLDER

SUPPORT LOCKING SCREW


Primary Mirror Alignment If both the secondary mirror and reflection of the primary mirror are centred, but

the mirror image and the reflection of the secondary are not centred like in the

image on the right, it will be necessary to adjust the Primary Mirror.

There are three pairs of thumb-screws on the back of the Primary Mirror. Loosen

the three smaller Primary Mirror Locking Screws by turning them anti-

clockwise by three turns or so, his will free the Primary Mirror and allow

alignment to take place.

Choose one of the three larger Primary Mirror Adjustment Screws and turn it

slightly while observing the changes through the Cheshire eyepiece. With

experience you should be able to get a feel about the effect the turning of the

Primary Mirror Alignment Screws will have.

It is sometimes advantageous if two persons undertake the alignment of the

Primary Mirror as one can gently rotate the Primary Mirror Adjustment Screws

while following the observer’s instructions.

Once the image appears central in the eye tighten the three Primary Mirror

Locking Screws. Take care at this point not to over tighten these screws as this

may slightly push the Primary Mirror and affect collimation. Some experienced

users sometimes use the Locking Screws to refine Primary Mirror alignment in this

way.

Now tighten the three Support-bolt Locking Screws (Secondary Mirror

Assembly) to finish.

To further improve the collimation of the ARX-200 you would now need to re-

check and possibly re-adjust the Secondary Mirror one last time before tightening

the fixings as outlined below. This last step is optional.

Secondary Mirror Final Adjustment A star can be used for this final adjustment. Slightly loosen the two Setting Screws by turning them anti-clockwise one to two turns. Then use the Micro-adjustment Knobs to perform any corrections. Once the Primary Mirror is centred in the Cheshire eyepiece lightly tighten both Setting Screws.

Finally, carefully put the Support Bolt Cap and two Micro-adjustment Caps back in place by screwing them in a

clockwise direction. This protects the delicate mechanisms from dust and moisture.

Collimating the ARX-200 on a Star To collimate the ARX-200 on a star you would need a motorised mount, the actual telescope, a 2-2.5mm eyepiece,

and steady atmospheric conditions. Use a magnification of around 45-50 times per inch of aperture if the weather

conditions allow it. It is advisable to first collimate the telescope indoors with a Cheshire eyepiece as this will save

time once outdoors.

Locate a 2nd-3rd magnitude star which ideally should be high up in the sky. If you do not have a motorised mount

you could choose Polaris. Alternatively, you could use an artificial star like the Opticstar Artificial Star XL which

would need to be situated at a minimum distance of 20 times the focal length of the telescope. The ARX-200 would

require a minimum distance of 16 meters (32 meters is recommended). Before you start let the telescope cool down

for say 30-45 minutes. This will substantially improve the image through the eyepiece.

A video camera attached to the scope will make the process markedly easier as adjustment and observation can take

place at the same time.

Primary Mirror Adjustment Screws

Primary Mirror Locking Screws


APPENDIX C

OPTICSTAR ARX-200 SPECIFICATION weight

Aperture 203mm

Focal ratio F3.9

Focal length 792mm

Primary mirror Parabolic

Corrector Four element, frat-field & coma corrector 470 grams

Optical tube Carbon fibre, Internally anti-reflection coated.

Focuser Dual speed 10:1, 2” Crayford

Focuser options 2” with 1.25” adapter & extension

Tube rings Dual rings with carrying handle and dovetail platform

Telescope Carbon fibre tube with focuser, rings, handle & dovetail 8.1 Kg

Tube length 79cm

Tube diameter 27cm

Eyepieces 25mm Plossl

Finder-scope saddle Yes

Finder-scope 9x50 illuminated (with bracket) 630 grams

Case carry case for OTA and accessories


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]

LOOKING AT OR CLOSE TO THE SUN WITH A TELESCOPE OR FINDERSCOPE WILL CAUSE INSTANT AND PERMANENT

DAMAGE TO YOUR EYES.

The designers of the Air Spaced Triplet ED Apo …...primary mirror, large 203mm aperture, corrected...

Documents

Transcript of The designers of the Air Spaced Triplet ED Apo …...primary mirror, large 203mm aperture, corrected...