1

panel (part 7), as shown right.STEP 2: Turn the assembled

rocker box panels on their side.Line up the circular base top(part 11) that has the 7predrilled holes against theassembled front and sidepanels, as shown below. HolesH1 and H2 match up with thepre-drilled holes in the unfinished underside of the right

side panel (part 7).Holes H3 and H4match up with thepre-drilled holes inthe underside of thefront panel (part 8),and holes H5 and H6line up with the pre-drilled holes in theunderside of the leftside panel (part 7).

Optical Tube Assembly1. Eyepiece2. Focuser3. Finderscope and quick-release bracket4. Secondary mirror and spider assembly5. Altitude bearing assembly and clutch knob6. Optical tubeRocker Box Assembly7. Side panel (1 of 2)8. Front panel9. Lift handle10. Eyepiece rack11. Circular base (top)12. Circular ground board (bottom)13. Feet (3 beneath ground board)

The Parts ofYour Astro-TechDobsonianTelescope

1

5

6

3

16

21

20

Focuser Close-Up14. Coarse focus knob

(1 of 2)15. Fine focus knob16. Focus lock & tension

adjustment knobs17. 2” eyepiece holder18. Thumbscrew19. 2” eyepiece20. Finderscope21. Finder collimating screw

(1 of 2)

Focuser Close-Up

15

14

17

18

19

Thank you for choosing this Astro-Tech Dobsonian re-flector. While it is simply-made, it has precision opticsand an easily-assembled design that makes it an excep-tionally good value in a large aperture telescope. YourAstro-Tech Dobsonian will open for you a window on aUniverse of entrancing celestial viewing and years oftrouble-free observing enjoyment.

astro-tech 8” & 10”Dobsonians

from Astronomy Technologies

Assembling Your Astro-Tech DobsonianYou will need a Phillips-head screwdriver to assemble

a few components of your scope. The hex head wrenchneeded to assemble the majority of the scopecomponents is included with your telescope.

FIRST, ASSEMBLE THE ROCKER BOXSTEP 1: The rocker box supports the optical tube. It

allows you to move the tube up and down (in altitude)and from side to side (in azimuth) so you can manuallyfind and track objects as they move across the sky.

Line up one of the rocker box side panels (part 7)with the rocker box front panel (part 8) as shown. Threadtwo of the self-tapping woodscrews through the assemblyholes in the side panel intothe pre-drilled holes in theunfinished vertical edge ofthe front panel to secure thepanels together. Tighten thescrews to a firm feel, but donot overtighten. Repeat withthe second rocker box side

This instruction sheet will provide you with informa-tion on how to assemble your new reflector, and how toproperly maintain your telescope so it can give you alifetime of observing enjoyment.

Please familiarize yourself with your telescope’s partsand functions before assembling it or operating it forthe first time.

4

2

7

9

811

13 12

10

87

STEP 1A

Assemblyholes

Holes foreyepiece rack

STEP 1B

7

8

Assemblyholes

STEP 211

H1

H3H2

H4H5

H6

Assembled panelsfrom Step 1

The center holeis not usedin this step

7

2

Thread the remaining 6 self-tapping wood screwsthrough holes H1 through H6 in the circular base andinto the predrilled holes in the undersides of the frontand side panels. Tighten the screws to a firm feel, butdo not overtighten.

STEP 3: Get a few books of equal thickness or twoblocks of wood and place them on the floor parallel toeach other and about a foot apart. Sit the rocker boxyou have assembled on the books or wood blocks sothe rocker box is raised off the floor and the previouslyunused center hole is between the blocks.

Slide the tubular center bearing bushing into the centerhole of the circular base top (part 11) from above. Thebushing will be a tight fit, requiring a tap or two with ahammer to fit it into place. Be sure the bushing lines upat right angles to the circular base, and not at an angle,before tapping it into place. A series of gentle taps areall that will be needed. Tap the bushing into the circularbase until it projects about 1/4” to 3/8” past theunderside of the circular base to act as a guide forassembling the components in the next step. Raisingthe rocker box assembly off the floor with the books orboards prevents you from gouging your floor as you tapthe bushing past the bottom of the circular base.

Do not use excessive force. A piece of heavy cardboard,multiple layers of newspaper, or a thin board laid on topof the bushing will protect the end of the bushing frombeing dented if your tapping becomes too exuberant.

STEP 4: Take the rocker box off the books or boardsand lay it aside. Move the books out of the way. Placethe remaining circular ground board (part 12) on theground.

The azimuth bearingassembly consists of twoidentical circular metalroller bearing plates(each with a hole in itscenter) and a separatecircular roller bearing,also with a hole in itscenter. The latter hasspokes and looks like a wagon wheel with dozens ofsmall tubular roller bearings set into its circumference.

Place the three roller bearing plates in a stack on theground board (part 12), aligning the holes in their centerswith the hole in the center of the ground board. Firstplace one of the two metal roller bearing plates on theground board, as shown in the Step 4A illustration above.Next, lay the roller bearing (the plate that looks like awagon wheel) on top of thefirst roller bearing plate,then place the second rollerbearing plate on top of theroller bearing itself, makinga roller bearing sandwich, asshown in the Step 4Billustration to the right. Be

sure the central holes in the roller bearing sandwichand the center hole in the ground board all line up.

It will help to have a second person assist you duringthe next step. Place the rocker box assembly over theroller bearing stack so that the tubular bushing projectingthrough the circular base lines up with the holes in theroller bearing stack and the ground board. Gently lowerthe rocker box assembly until the tubular center bushingslips through the holes in the roller bearing stack andinto the hole in the ground board.

Repeat the tapping of the tubular center bushing witha hammer from the top side of the rocker box until thetop of the bushing is flush with the surface of the circularbase top (part 11) and fits securely into the hole in theground board. Be sure to observe all of the padding andgentle tapping precautions mentioned previously whendoing this final tapping of the center bushing.

STEP 5: To secure the rocker box to the ground board,use the hardware shown in the illustration below. Slidethe small washer onto the knob, followed by the smallroller bearing, and thenthe large washer. Slidethe knob into thebushing that you havetapped into the circularbase of the rocker boxassembly and thread itinto the lock nut thatwas factory-installedinto the underside ofthe ground board. Besure the large washer ison the bottom of thestack between the surface of the circular base of therocker box and the small roller bearing. Loosely hand-tighten the knob, but do not overtighten.

STEP 6: Next attach the three rubber feet to theground board. Tilt the rocker box assembly on its side.Using a Phillips head screwdriver, screw one of the shortself-tapping wood screws through each foot into the pre-drilled holes in the ground board. Tighten to a firm feel.

STEP 7: Install the lift handle (part 9) by using thesupplied hex head wrench to thread the supplied boltsthrough the handles and into the pre-drilled holes in thefront panel of the rocker box.

STEP 8: Sit the rocker box upright on the floor. Swivelthe rocker box from side to side on the ground board. Itshould move easily, without any stiffness. If not, slightlyloosen the knob you installed in Step 6 until you achievethe ease of motion you prefer.

STEP 9: The supplied eyepiece rack (part 10) can beinstalled on the side panel of the rocker box, using thesupplied wood screws to fasten it to the two holes pre-drilled into the side panel.

NEXT, ASSEMBLE THE OPTICAL TUBESTEP 10: With the rocker box resting upright on its

feet, place the optical tube into the rocker box. MakeSTEP 4B

STEP 5

Large washeron bottom

Roller bearingin middle

Knob

Smallwasheron top

Hole in rockerbox base with

bushing inserted

Toproller

bearingplate

STEP 4A

12

Rollerbearingplate

Assembledrocker box

Rollerbearingin center

Bottomroller

bearingplate

11

3

The focuser hasseparate lock andtension knobs, asshown right. Thelock knob allowsextended observingwith very heavyeyepieces withoutfocus shift. Thetension knob ad-justs the drawtubefriction so you canswitch between avariety of eyepieceswithout having the heavier eyepieces drift out of focus.

STEP 13: The altitude bearings have been set at thefactory to balance a wide range of eyepiece weightswith the help of the altitude clutch knobs, which adjustthe freedom of tube motion up and down (in altitude).However, if you have mostly heavy eyepieces in yourobserving kit, you may want to adjust the tube balance.

Put your heaviest eyepiece in the focuser, lower theoptical tube until it is parallel with the ground, and loosenthe altitude clutch knobs. Note whether the eyepieceend of the tube rises or falls when you let the tube go.

Lift the optical tube out of the rocker box and set it onthe ground. Note each bearing’s location on the scaleand loosen the balancelock screws on thealtitude bearings oneither side of the tube.

If the nose of theoptical tube rose whenit was parallel to theground, the tube is tailheavy. Slide the altitudebearings back (towardsthe primary mirror) aline or two on the scale on each side to shift the tube’scenter of gravity back. Tighten the balance locks. If thenose of the optical tube sank, it is nose heavy. Slide thealtitude bearings slightly forward (towards the focuser)and tighten in place. Put the optical tube back in therocker box and check the balance. Readjust the altitudebearing positions as needed, being sure both altitudebearings line up with the same scale markings.

STEP 14: A battery pack is provided to power thebuilt-in primary mirror cooling fan. The battery pack holdseight AA batteries (not supplied). Alternatively, anyrechargeable battery pack with a 9 to 12VDC outputand a 5.5mm female power plug can be used to powerthe fan. While the low-vibration fan can be left pluggedin and running continuously without affecting yourobserving, it will deplete AA batteries quickly. Unpluggingthe fan after mirror cooldown should be considered tosave your batteries if you use the battery pack.

STEP 15: Enjoy your scope!

sure that the U-shaped altitude ball bearing and clutchknob assemblies are oriented properly to fit snugly downinto the U-shapedopenings on the sidepanels of the rockerbox, as shown in theillustration to theright. Also, makesure that the seamon the optical tube ispointing at the frontpanel of the rockerbox. Leave the dustcover on the scopeto protect it until you are ready to observe.

The large ribbed altitude clutch knob that projects fromeach altitude bearing assembly allows you to adjust theamount of friction within the altitude bearing. This letsyou compensate for eyepieces of differing weights whenobserving, by keeping the tube from slipping or driftingin altitude when you switch between eyepieces.

STEP 11: Locate the finderscope, finderscope bracket,and rubber O-ring supplied with the bracket. Slip the O-ring over the 8 x 50mm finderscope body and slide itforward until it rests in the groove in the body.

Loosen the two plastic collimating screws on thefinderscope bracket and slide the finderscope into thebracket from the front until the rubber O-ring on thefinder seats firmly in the groove in the front of thebracket. Tighten the collimation screws temporarily.

Slip the finder bracketinto the mounting shoeon the optical tube asshown right and tightenthe knob in the mountingshoe to hold the bracketin place. The finder’s twonylon collimating screwswork in conjunction witha tension spring in thebracket to make it easyto collimate the finderscope with the main scope optics.

STEP 12: The dual-speed Crayford focuser has beeninstalled at the factory. If you wish to use the supplied2” eyepiece, or any other 2” eyepiece you may have,remove the 1.25” eyepiece adapter from the focuserassembly by loosening the thumbscrew of the 2”eyepiece holder (shown at the top of the next column).Slide the 2” eyepiece into the focuser and tighten thethumbscrew. To focus quickly, turn either of the coarsefocusing knobs. For very precise focus (for highmagnification observing, for example) use the singlesmaller black fine focus knob.

To use the supplied 1.25” 9mm eyepiece, or any other1.25” eyepieces you may have, replace the 1.25”eyepiece adapter in the 2” eyepiece holder and tightenthe thumbscrew to hold it in place.

STEP 10

Seam

Altitudebearing

assembly

Front ofrocker box

Altitudeclutchknob

Opticaltube

STEP 11 Finderbracket

Mountingshoe

Tensionspring

Collimating screw

STEP 12

Finderand

bracket

Tube lock knobCoarse focus knob

Coarsefocusknob

Finefocusknob

Tubetensionknob

Thumbscrew

Balance lockscrew

Scale

Altitude bearingClutchknob

STEP 13

4

Figure A: Identifying the components seenthrough the focuser drawtube

Bottom end offocuser drawtube

Diagonalmirror holder

Reflectionof your eye

Spidervane

Primarymirrorcenterdonut

Edge ofdiagonal mirror

Reflectionof primary

mirror

Primarymirror

clip

Off-centerdiagonal mirror

Bottomof drawtube

Bottomof drawtube

Diagonalnow centered

COLLIMATING YOUR SCOPEAccurate mirror alignment is important to ensure the

peak performance of your telescope. For the best imagequality, the alignment of your telescope mirrors shouldchecked and adjusted as needed (i.e., collimated) on aregular basis.

Although your Astro-Tech Dobsonian optical tube wascollimated at the factory, you should check collimationbefore using it the first time to ensure that rough handlingin shipment has not altered the alignment of the mirrors.Your scope uses a no-tool six-knob locking push/pullprimary mirror cell that reduces the need for frequentcollimation, but a quick check of the collimation (andtweaking, if needed) should be a regular part of yourscope set-up routine, particularly if you routinelytransport your scope to a dark sky observing site.

While collimation can be done solely by eye as shownhere, optional tools (such as a Cheshire eyepiece, acombined Cheshire eyepiece/sight tube, or a lasercollimator) will make the job easier and quicker.

The center of your scope’s primary mirror has beenmarked with a donut-shaped sticker to make collimationeasier. This center mark is required for best results witha Cheshire eyepiece or laser collimator. The center ringsticker should not be removed from the primary mirror.Because it lies directly in the shadow of the diagonalmirror, it cannot be seen in the eyepiece and its presencein no way affects the optical performance of your scopeor the image quality.

To check collimation by eye, remove the eyepiece andlook down the focuser drawtube. You should see thediagonal mirror centered in the drawtube, as well asthe reflection of the primary mirror centered in thediagonal mirror, and the reflection of the diagonal mirror(and your eye) centered in the reflection of the primary

mirror. You can identify the various parts in Figure A inthe previous column. Ignore the reflections for the timebeing and start by examining the diagonal mirror, whichshould be centered in the focuser drawtube.

If the diagonal is not centered in the focuser drawtube,it may look similar to Figure B. If this is the case, itneeds to be adjusted.This adjustment wil lrarely, if ever, need to bedone, however. It helpsto adjust the diagonalmirror in a brightly litroom with the scopepointed toward a brightsurface, such as a whiteor light-colored wall.Placing a sheet of whitepaper in the telescope tube opposite the focuser (i.e.,behind the diagonal mirror) will also be helpful incollimating the diagonal.

If the diagonal mirror is not directly under the focuserdrawtube fore and aft, loosen the three small alignmentset screws in the center hub of the 4-vaned spider severalturns. Holding the diagonal mirror holder stationary(being careful not to touch the surface of the mirror),turn the center screw in the center hub. Turning thescrew clockwise will move the diagonal mirror towardthe front opening of the optical tube, while turning thescrew counter-clockwise will move the diagonal mirrorback towards the primary mirror. DO NOT LOOSEN THECENTER SCREW TOO FAR. This screw attaches the mirrorholder to the spider. If it is unscrewed too far, it canallow the diagonal mirror assembly to fall onto theprimary mirror, causing mirror damage that is not coveredby warranty.

When making these adjustments, be careful not tostress the spider vanes or they may bend.

If the diagonal mirror is centered fore and aft underthe focuser drawtube, but is turned to one side or theother, it will look like an oval, rather than a circle. Rotatethe diagonal mirror holder until the reflection of thediagonal is circular and the primary mirror is centered inthe diagonal as much as possible. The primary may notbe perfectly centered, but that is acceptable if thediagonal mirror appears circular. Now retighten the threesmall alignment screws in the spider’s center hub equallyto secure the diagonalmirror in that position.

If the entire primarymirror reflection is notvisible in the circulardiagonal mirror, as inFigure C, you will needto adjust the tilt of thediagonal mirror.

This is done byalternately loosening

5

astro-tech www.astronomytechnologies.comfrom Astronomy Technologies, 110 East Main, Norman, OK 73069

© 2012 by Astronomy Technologies Specifications, features, and descriptions are effective 6/1/2012, but are subject to correction and/or modification without notice and/or obligation.

Diagonalcentered Primary

centered

Diagonalcentered

Primarycentered

one of the threealignment setscrews inthe spider’s center hubwhile tightening theother two. The goal isto center the primarymirror reflection in thediagonal mirror, as inFigure D. Don’t worryif the reflection of thediagonal mirror (andyour eye) is off-center, or not under the collimating donut,as seen in Figure D. You will fix that in the next step.

The final adjustment is made to the tilt of the primarymirror. It will need adjustment if, as in Figure D, thediagonal mirror is centered under the focuser and thereflection of the primary mirror is centered in the diagonalmirror, but the small reflection of the diagonal mirrorand your eye is not under the collimating donut. This isthe collimation adjustment that is most likely to needtweaking occasionally to maintain the best images.

The primary mirror tilt is adjusted with the three largespring-loaded collimation thumbscrews on the back endof the optical tube (bottom of the primary mirror cell).The three smaller thumbscrews lock the mirror’s positionin place once it is collimated. These smaller thumbscrewsmust be loosened before any collimation adjustmentscan be made to the primary mirror.

To start, turn the smaller locking thumbscrews a fewturns each counterclockwise to loosen them. Now, trytightening or loosening one of the larger collimationthumbscrews to see the effect. Normally motions onthe order of 1/8 turn will make a difference, with onlyabout 1/2 to 3/4 turn being the maximum required. DoNOT remove or back out the collimation screws morethan one to two turns! Look into the focuser and see ifthe diagonal mirror reflection has moved closer to thecenter of the primary. You can tell this easily with themirror collimation donut by simply watching to see ifthe reflection of your eye is moving closer or fartheraway from the donut on the center of the primary mirror.

When the reflection ofyour eye is centered inthe collimation donut,your primary mirror iscollimated. The viewthrough the drawtubeshould resemble FigureE. Retighten the lockingthumbscrews.

For the sharpestimages, a simple startest will let you perfect your collimation, but perfectionis not essential for casual backyard observing.

THE STAR TESTYour telescope should be set up outside at night for

30 to 45 minutes before attempting collimation. Waitfor a night with good seeing conditions (cloudless skies,calm air) and avoid looking over anything that producesheat waves (i.e., roof tops, car hoods, etc.).

Collimation adjustments are best made while viewingthe star’s position in the field of view while simultanouslyturning the adjustment screws. This way you can seeexactly in which direction the movement occurs. It ishelpful for two people to work together when collimating,with one viewing and instructing the other which screwsto turn and by how much.

Point the telescope at a bright star and center it in theeyepiece field of view. Study the image of the star whileracking it in and out of focus using 30 to 60 power perinch of aperture (a 3mm or 4mm eyepiece). If thetelescope is correctly collimated, the star’s expandingdisk and diffraction rings should be a perfect circle oneither side of focus (theleft image in Figure F).If you notice a flare toone side of the star (theright image in Figure F)as you go inside andoutside of exact focus, then tweaking the collimationwill help sharpen the image.

Take note of the direction of the flare. For example, ifthe flare is toward the 3 o’clock position in the field ofview (to the right), then you must adjust the screw orcombination of screws necessary to move the starTOWARD the direction of the flaring. In this case, youwould want to use the adjusting screw or pair of screwsto move the star to the right, toward the 3 o’clock positionin the eyepiece field of view.

After making each adjustment, re-aim the telescopetube to center the star again in the field of view. Onceagain rack the scope focuser to either side of exact focusand note the symmetry of the star ’s pattern.Improvement should be seen if the proper adjustmentshave been made. You may have to adjust the screw orscrews several times to achieve the necessary directionand amount of mirror movement.

If you try the star test and the bright star you haveselected is not accurately centered in the eyepiece, theoptics will always appear out of collimation, even thoughthey may be perfectly aligned. It is important to keepthe star precisely centered, so you will need to makeslight corrections to the telescope’s position over timein order to account for the sky’s apparent motion.

Polaris, the North Star, is the perfect collimation starfor northern hemisphere observers since it appearsmotionless against the background sky long enough toperform the collimation procedure.

Eye and collimation ringcentered

F

Eye not centered under donut

Donut

Bottom of drawtube

6

ASTRO-TECH DOBSONIAN ROCKER BOX ASSEMBLY DIAGRAMThe parts designated by numbers refer to the larger

visible parts shown in the main illustration on Page 1and the construction photos on Pages 1 and 2.

The parts designated by letters refer to the smallerhidden assembly parts shown in the construction pho-tos on Page 2 and the Parts List on Page 7.

7L

7R

11

12

N

O

8

F

K

J

I

S

R

9

L

10

G

R

Q

H

© 2010 by Astronomy Technologies

7

ASTRO-TECH DOBSONIAN ROCKER BOX PARTS LIST

Left Side PanelPart 7L

Right Side PanelPart 7R

Front PanelPart 8

Circular Base (Top)Part 11

Ground Board (Bottom)Part 12

Rocker Box Wood Parts

Rocker Box Hardware Parts

Roller BearingPlate Top(1 of 2) Part R

Roller BearingPart S

Roller BearingPlate Bottom(2 of 2) Part R

Tubular CenterBushing Part G

32mm WasherPart F

5/16” - 18Adjustment KnobPart I

16mm Washer Part J

15mm Roller BearingPart K

The parts designated by numbers refer to the largervisible parts shown in the main illustration on Page 1and the construction photos on Pages 1 and 2.

The parts designated by letters refer to the smallerhidden assembly parts shown in the construction pho-tos on Page 2 and the Assembly Diagram on Page 6.

LongSelf-TappingWood Screws(quantity 10)Part H

Short Self-TappingWood Screws (quantity 3)

Part O

Short Self-Tapping WoodScrews (quantity 2)

Part Q

1/4”-20 Machine Screws(quantity 2) Part L

Plastic Feet(quantity 3)Part 13

Eyepiece RackPart 10

Lift HandlePart 9

© 2010 by Astronomy Technologies