VIII. Improve Alignment

The polar alignment procedures in the previous section are sufficient for
visual observing, and for photography of bright objects like the Moon
or Venus. The steps in this guide are necessary to perfect the alignment
for just about everything else. There are several ways to do this, but the
method that seems best suited for my equipment is the DSLR method. If followed
all the way through to the PEC method, a very accurate alignment should be
obtained. If long exposures cannot be obtained, say under extensive light
polution, perhaps a two or five minute interval between exposures is sufficient.
See Orientations and Alignments.

The basic idea in this procedure is to take exposures in pairs, and to
evaluate how stars drift between the two exposures. At first, the interval
between the two exposures is low (2 minutes). A drift error becomes more
noticable as time increases. After noticable drift is eliminated in two
exposures taken two minutes apart, the interval is increased to five
minutes. And finally drift is eliminated in exposures taken at 8 minute
intervals. Of course, accuracy can be improved even more by selecting even
longer intervals.

  1. Turn on camera and set to B and ISO 6400s
  2. Set up intervalometer:
    1. Self: 0
    2. Int: duration between exposures. Start with 2 minutes, then proceed to five
      and 8 minutes as drift is refined.
    3. Long: 6 seconds (ensure that the sensor completely off loads between images)
    4. Frames: 2
  3. Azimuth:
    1. Point the telescope near the intersection of the Equator and Meridian
    2. Orient the camera so that the wide dimension of the frame is parallel
      to the right ascension axis
    3. Set hand controller switches to match movements on the camera display
    4. Take a pair of exposures with the intervalometer setting above
    5. Use thumb wheel on back of camera to compare star movements from the first
      exposure to the second exposure
      1. Ignore east-west drift
      2. If the star drifts north, then adjust the azimuth toward the east
      3. If the star drifts south, the adjust the azimuth toward the west
      4. Repeat step c. until drift is satisfactory at that Int setting
      5. Increase Int from 2 to 5 minutes, or from 5 to 8 minutes
      6. Repeat until drift is eliminated at 8 minutes between exposures
  4. Elevation:
    1. Slew the mount on the declination axis only to the eastern or western horizon
    2. Take a pair of exposures with the intervalometer setting at 2 minutes
    3. Compare drift in the first and second exposures
      1. Eastern Horizon
        • If the star drifts south, then adjust the elevation upward
        • If the star drifts north, then adjust the elevation downward
      2. Western Horizon
        • If the star drifts south, then adjust the elevation downward
        • If the star drifts north, then adjust the elevation upward
    4. Repeat until all discernible drift is removed a 2, 5, and 8 minute intervals
  5. PEC Method (eight minute cycle)
    1. Find and center a bright star near the object to be photographed
    2. Study the periodic movement for a few moments, and practice guiding to
      keep the star centered
    3. Select the .3x guiding rate on the control panel
    4. Wait until the star has been centered for a few seconds, and then press
      the PEC button to activate. The LED will flash once a second for five seconds
      before it begins recording corrections
    5. Recording will end after eight minutes (the LED stops blinking), and then
      the system will start playing back the corrections