20+inch+F3.8+Dobsonian+Operation+and+Maintenance


 * Assembly:-**
 * 1) Place the rocket box down onto hard flat level ground.
 * 2) Place the mirror box down onto the rocker box (no weights to be installed). The altitude bearing lateral skids sit inside the rocker box.
 * 3) Fix the eyepiece side double truss (this has short thread) do not tighten.
 * 4) Fix the double truss opposite to eyepiece (has long thread and no Velcro attached) do not tighten.
 * 5) Put on top cage and fix to the trusses with hand wheels.
 * 6) Fix the lower side double truss (this has long thread ad no Velcro) TAKE CARE NOT TO HIT SECONDARY. Pass up into cag fixing hole. Do not tighten.
 * 7) Fix top side double truss (this has long thread and DES has Velcro) TAKE CARE NOT TO HIT SECONDARY. Pass up into cag fixing hole. Do not tighten.
 * 8) Nip up all mirror box hand wheels and top cage hand wheels.
 * 9) Lower the tube in altitude onto chair a (or somebody hold the top end), then add the lower counter weights.
 * 10) Raise the tube and fix upper and lower baffle extensions.


 * Collimation:-**
 * 1) Lower the tube over to 45 Deg altitude.
 * 2) Remove the secondary mirror cover.
 * 3) Lift the primary mirror cover and ensure mirror is centred in its cell. If it’s not, then raise the height of mirror in cell first. Loosen the inner hand wheel at the left hand side at the rear of the mirror box slightly (do not completely loose) then adjust height of mirror in cell with the outer hand wheel. Then tighten inner hand wheel while holding the outer hand wheel in position so it does not rotate and change the height of the mirror.
 * 4) Then adjust the left/right position of the mirror in it’s cell by sliding the mirror on the mirror support pads. When centred, raise the altitude to the zenith and back a few times to release any support induced stress from adjustments made.
 * 5) Collimate the system with an alignment laser that has a return target built in.
 * 6) Ensure that the secondary spot has the outgoing laser on top of it. If not, first check axial alignment (this should not need adjusting). If adjustment is required then the centre bolt fixing to the secondary holder will need adjustment together with the 3 secondary wing nuts to adjust the distance of the secondary holder from the spider support.
 * 7) Adjust rotation of the secondary by slightly loosening the 3 secondary collimation bolts and by hand rotate the secondary so that the laser is centred on the secondary, and nominally centred on the mirror also. Fine adjustment of the spot to the mirror is done next.
 * 8) Then adjust the 3 wing nuts on the secondary so that the laser is centred on the primary mirror. Re-check that the laser is still centred on the secondary spot.
 * 9) Then adjust the 3 primary mirror cell collimation hand wheels on the rear of the mirror box to bring the return beam back to the laser alignment tool target.
 * 10) Finally, on-sky centre a bright star a de-focus (outside of focus) to see the pupil. Make fine adjustments to the mirror cell collimation hand wheels so that the shadow of the secondary is centred on the illuminated pupil. Ensure that the star is in the centre of the field when checking for this. The object of this exercise is to have the ‘sweat spot’ in the centre of the field.


 * Dis-assembly:-**
 * 1) Lower the mirror cover.
 * 2) Fit the secondary mirror cover.
 * 3) Remove the upper and lower top end cage baffle extensions.
 * 4) Lower the tube onto a chair (or somebody hold the top end) to remove the counterweights.
 * 5) Raise the tube to the zenith.
 * 6) Loosen but do not remove all hand wheels on the mirror box and top end cage.
 * 7) Remove the upper and lower double trusses and had wheels. TAKE CARE NOT TO HIT THE SECONDARY MIRROR.
 * 8) Remove all hand wheels securing the top end cage and then remove the top end cage.
 * 9) Remove the last two double trusses.
 * 10) Lift the mirror box off the rocket box.