BAS 16 Telescope Manual Rev 1 Assembly Manual for the Brevard Astronomical Society 16 inch F4.5 Dobsonian Telescope Brevard Astronomical Society P.O. Box 1084 Cocoa, FL 32922
TABLE OF CONTENTS SECTION I: TELESCOPE ASSEMBLY... 2 SECTION II: TELESCOPE COLLIMATION... 7 SECTION III: TELRAD FINDER ALIGNMENT... 13 SECTION IV: TELESCOPE TEARDOWN... 14 APPENDIX A: B.A.S. 16 inch Telescope Part Names... 15 PURPOSE This manual outlines the steps required to assemble and align the Brevard Astronomical Society (BAS) 16 inch Dobsonian Telescope. Photographs of individual pieces are located in Appendix A for those unfamiliar with the parts. Please become familiar with part names prior to assembly. CAUTION The telescope Mirror Box will require heavy lifting. The use of two people to lift the Mirror Box is recommended. USE PROPER LIFTING TECHNIQUE. Leave the Protective Mirror Cover in place for protection until directed to remove it. Telescopes are optical instruments and therefore should be treated with care. 1
SECTION I: TELESCOPE ASSEMBLY 1. Position the Rocker Box onto a level observing area with at least 6 feet of clearance around all sides. 2. Place Mirror Box into the Rocker Box as shown in Photo 1. The flat vertical side with Teflon pads faces the Rocker Box center side panel. The Mirror Box is very heavy, therefore use proper lifting technique. Photo 1 Mirror Box installed in Rocker Box NOTE: The two Wheel Brackets may be attached to the Rocker Box sides (with Mirror Box inside) in order to move them over longer distances. See Photo 2. Remove the Wheel Brackets when positioned at your observing location. Photo 2 Wheel Bracket Installation 2
3. Install four Truss Rods onto Mirror Box as shown in Photos 3-5 using the following guidelines: a) Leave the Protective Mirror Cover in place. b) During the installation steps, allow the telescope assembly to point upwards. c) The Truss Rods (Photo 3) are numbered 1 through 4 and fit into the appropriate Mirror Box sides (Each side is also numbered 1 through 4). d) The Truss Rods are to be installed with the numbers facing inward. This will help to minimize adjustments (collimation) once the telescope is assembled. e) Tighten 8 Truss Rod screws (2 per side) to hold the Truss Rods to the Mirror Box. Photo 3 Truss Rod Numbering Photo 4 Truss Rod Mounting Photo 5 Truss Rod Installation 3
4. Attach the Secondary Cage to the top of the four Truss Rods as shown in Photos 6-7: a) The Secondary Cage is also numbered 1 through 4. b) Number 1 position (near focuser) aligns to Truss Rod 1. c) Tighten 4 screws (1 per Truss Rod) to hold the Secondary Cage to the Truss Rods. # 1 position Photo 6 Truss Rod # 1 Photo 7 Secondary Cage Installed 4
5. Carefully remove the Protective Mirror Cover from the Mirror Box and set aside at a clean, dry location. See Photo 8. The telescope may now be safely tilted as required. Photo 8 Protective Mirror Cover Removal 6. Slide the black shroud from the top to the bottom over the entire length of Truss Rods. This will block extraneous light from entering the optical path. See Photo 9. Photo 9 Shroud Cover 5
7. Install the battery: a) Tilt the telescope downward and set the battery inside the Mirror Box corner as shown in Photo 10. b) Route the Red/Black wires from under the Mirror Box and connect the black wire to the black battery terminal, and the red wire to the red battery terminal. The Dew Heater on the Telrad Finder obtains power from the battery. NOTE: The telescope can be used without the battery, but the Telrad Finder dew heater will not operate. Photo 10 Battery Hook-Up 8. Install the Telrad Finder as follows: See Photo 11. a) Loosen the two side screws on the Telrad base mounted on the Secondary Cage. b) Insert the Telrad Finder and then tighten the two base screws. c) Connect the yellow power plug into the Telrad Finder as shown in Photo 11. Wrap cable under finder Connect cable here Photo 11 Telrad Finder Telescope assembly is complete. 6
SECTION II: TELESCOPE COLLIMATION PURPOSE: Collimation is the adjustment of the optical components in order to bring them into alignment with each other. This will improve performance of the telescope just as a musical instrument is tuned before use. NOTE: For more detailed information on telescope collimation, refer to one of several websites or articles on the process. One such reference is Sky and Telescopes (www.skyandtelescope.com) How To Collimate Your Newtonian Reflector by Nils Olof Carlin. The BAS 16 telescope should not require major adjustments as long as: the assembly process is followed, no mirrors have been physically removed or no previous major mis-alignments have occurred, or no damage/rough handling of the telescope has occurred. Some trial and error will be needed to become familiar with the technique. There are three main steps to collimating the telescope: Step 1 Step 2 Step 3 Centering of the secondary mirror on the axis of the focuser drawtube. Adjusting the secondary mirror tilt to aim the focuser s axis at the center of the primary mirror. Adjusting the primary mirror to center its optical axis in the focuser. Collimate the telescope as follows: 1. Center the Secondary Mirror NOTE: The BAS 16 inch telescope should not require this adjustment unless the secondary mirror has been accidentally moved. Do not adjust the secondary Mirror center screw/wing-nut unless you are thoroughly familiar with the telescope and technique. Verify the centering of the Secondary Mirror in steps a - d below and then skip to step 2. a) Remove the 1 ¼ eyepiece adapter and rack the focuser all the way in. b) Look through the focuser with your eye about 6-8 inches from the focuser. c) Verify that the Secondary Mirror edge appears circular and evenly centered in the focuser drawtube inner diameter. See Photo 12 for reference. d) The center Secondary Mirror wing-nut (see Photo 13) should already be locked into place with no adjustment required. Skip to Step 2 after verifying this alignment. 7
e) If the mirror has been accidentally moved or inaccurately adjusted earlier, loosen the center secondary wing-nut and rotate the mirror as required to center the mirror in the focuser tube diameter. f) Re-tighten the wing-nut while checking the alignment as described in steps a c. Secondary Mirror edge evenly centered within focuser drawtube edge Focuser drawtube edge Photo 12 Focuser & Secondary Mirror Alignment Check Secondary wing-nut Photo 13 Secondary Mirror Wing-Nut Location 8
2. Adjust Secondary Mirror Tilt a) Rack the focuser all the way out. b) Install the Laser Collimator into the focuser as shown in Photo 14 and turn it on. The laser requires 2 AA batteries. c) Tilt the telescope so the front opening is at a comfortable position to visually see the Primary Mirror and the Secondary Mirror adjustment screws. CAUTION: Do not point the laser at a persons face or look into the laser. Telrad Dew Heater Power Switch Laser Collimator Power Switch Photo 14 Laser Collimator Installed d) Adjust the 4 Secondary Mirror holder screws to align the laser red dot onto the Primary Mirror center (white ring). Use the following guidelines and Photos 15 and 16 to help make this adjustment. The top and bottom screws are used to adjust the laser red dot vertically. The left and right screws are used to adjust the laser red dot horizontally. Adjust 2 opposite screws (left/right, or top/bottom) at the same time. One is turned clockwise while the opposite screw is turned counter-clockwise at the same time. Photo 15 shows the expected movement of the red laser dot on the primary mirror when adjusting these 4 screws. Only very small adjustments are made at one time (fractions of a turn) until the red laser dot is centered in the mirror. e) Photo 16 shows this alignment with the red laser dot centered in the Primary Mirror (jnside small adhesive ring at center of mirror). 9
CW = Down CCW = Up CW = Right CCW = Left CW = Left CCW = Right CW = Up CCW = Down Photo 15 Secondary Mirror Adjustment Screws (Expected movement of red laser dot on Primary Mirror) Red Laser dot in Primary Mirror Center Photo 16 Secondary Mirror Tilt (Laser Beam Centered on Primary Mirror Center) 10
3. Adjust Primary Mirror a) Turn on the laser collimator and while looking into the telescope front opening, verify that around the bottom of the focuser or laser collimator circular face, a red laser return dot is seen. This should be somewhat close to the laser collimator as shown in Photo 17. If it s not seen, move a piece of paper around inside the telescope near the focuser to locate the return of the laser red dot. b) Adjust the 3 Primary Mirror screws (located behind the mirror at bottom of Mirror Box) to align the laser red dot so that it coincides with the laser output hole. Use the following guidelines and Photos 17-19 to help make this adjustment. The process is more efficient with two people; one adjusting the 3 screws, and the other directs the adjustment while watching the red laser dot near the laser collimator. Photo 19 shows the expected general movement of the red laser return dot near the laser collimator when adjusting these 3 screws. Only very small adjustments are made one at a time (fractions of a turn) until the red laser return dot coincides with the laser output hole. c) Photo 17 shows alignment slightly off center, and Photo 18 shows the completed alignment. The goal is to have the laser light going down the path of the telescope return the same path to the laser collimator. d) After the red laser dot is centered, verify the laser is still centered on the Primary Mirror. If not, make minor adjustments per step 2, and then repeat step 3 again as required. e) Turn the laser collimator off and remove it from the focuser. 11
Red laser return dot off-center. Move to center. Red laser return dot may be initially more off-centered than shown. Left Up Right Down Photo 17 Laser Collimator (adjustment slightly off-centered) Photo 18 Laser Collimator: Centered. (Primary Mirror Screw Adjustment affect) CW = Up CCW = Down CW = Right CCW = Left CW = Left CCW = Right Photo 19 Primary Mirror Adjustment Screws (General movement of red laser return dot seen near Laser Collimator) 12
SECTION III: TELRAD FINDER ALIGNMENT Align the Telrad Finder as follows: See Photos 20-21. 1. Insert an eyepiece into the focuser and finger tighten the two holder screws. NOTE: When using 1 ¼ eyepieces, insert the 2 to 1 ¼ Eyepiece Adapter unless already installed. 2. Adjust the telescope to view (focus and near center field of view) a bright star or a distant object on land. 3. Turn on the Telrad Power switch and adjust the intensity of the red concentric circles as desired while looking through the finder. 4. Compare the view in the finder with the eyepiece view, and adjust the 3 Telrad adjustment screws (located on back side of finder) to center the bright star/object within the red concentric circles while the object is near the eyepiece center field of view. Some trial and error will be needed to become familiar with the technique. Power Switch & Intensity Adjust Up/Down Left/Right Photo 20 Telrad Finder Adjustment Screws Photo 21 Telrad Finder Alignment (Centered on bright object) The telescope is now ready to use. 13
SECTION IV: TELESCOPE TEARDOWN 1. Disconnect Battery power wires and store battery. 2. Disconnect the Telrad Finder power wire and loosen the 2 side screws, and remove the finder and store it. 3. Remove eyepiece from focuser if one is inserted. Adjust the focuser so the barrel is all the way in. 4. Tilt the telescope into a vertical position. 5. Slide the black shroud up to and over the Secondary Cage as seen in Photo 7. 6. RE-INSTALL THE PROTECTIVE MIRROR COVER. 7. Remove the Secondary Cage by loosening the 4 screws (1 per rod) and carefully lift it from the Truss Rods. Store the Secondary Cage. 8. Remove the 4 Truss Rods by loosening the 8 screws (2 per side). Store the Truss Rods. 9. The Mirror Box and Rocker Base may be moved together with the Wheel Brackets installed, or carried by two people. Or, the Mirror Box may be lifted out of the Rocker Box and both moved individually. CAUTION The Mirror Box is heavy, therefore use proper lifting techniques. 10. Store the Truss Rod Screws in the storage container as seen in Appendix A. 11. Store the telescope parts in a clean, dry area. 14
APPENDIX A: B.A.S. 16 inch Telescope Part Names Rocker Box with Ground Board Mirror Box with Cover Secondary Cage w/shroud Truss Rod Screws 2 to 1 ¼ Eyepiece Adapter Truss Rods (4) Telrad Finder Laser Collimator Wheel Brackets 15