Aligning with the Scheiner-method

Alignment using the Scheiner-method

Work steps before error correction

If there is no clear view of Polaris and nevertheless long exposure times have to be realized for astrophotography, the Scheiner-method (named after Julius Scheiner) can be used.

Before starting with that method, the telescope must be set into the tracking mode. To do this, you can switch from terrestrial to astronomical observation in the menu of the hand control box, for example, or you can give the command for tracking directly. If the menu does not offer this possibility, a so-called "Easy Align" can be started by the approximate alignment at the beginning (see menu point 'Proceeding' - 'Setting up and wire').
The mount automatically moves to two stars after selection in the menu of the hand control box, which must be confirmed. (For calling the command, follow the respective operating instructions of the mount). After moving to the first star, the tracking starts automatically. Here you should also focus immediately (see menu item 'Proceeding' - 'Focusing with the Bahtinov-mask').

Note: Sometimes the "3-Star" or "1-Star Alignment" can be selected in the menu of the hand control box. With the "3-Star Alignment" possible cone errors (orthogonality errors between the axes and the optical axis of the tube) are calculated out very well. The "1-Star Alignment" is somewhat less accurate.

The following prerequisites or conditions are assumed: (see menu point 'Basics' - 'Theoretical basics of the Scheiner-method')

    • Azimuth correction: selection of a south star at the meridian (not at the zenith)
    • Pole elevation correction: Selection of a star in the west
    • Use of an eyepiece without using accessories (zenith mirror, Amici prism or similar)

 

Correction of the azimuth error

StepDescriptionIllustration
(1)
  • From the home position, move the telescope along the meridian.
  • To do this, place the counterweight rod horizontally.
  • Since a star in the west is to be approached during the subsequent polar altitude correction, the tube should be on the opposite side in the east. [1]

Approximate position of the telescope when searching for a star at the meridian in the south near the celestial equator [2]
(2)
  • slew to the celestial equator
  • (→ from the home position by 90° towards the south or align the tube horizontally towards the south, and then slew the telescope upwards by '90° - pole height')
  • select a suitable star near the meridian (+/-1,5°) and the celestial equator (+/-5°) [3]

Selection of a star near the meridian and the celestial equator
(3)
  • Combine a crosshair eyepiece with a Barlow lens (make sure the magnification is reasonable: approx. 25 - 1.5 x aperture in mm) [1]
  • Move to and center the selected star by rotating the declination axis (manually or via hand control box).
  • Since you are looking in the direction of the south, east is on the left and west is on the right!
Celestial points are inscribed as seen with the naked eye


Star centered in crosshair eyepiece

(4)
  • Align the horizontal line of the crosshair eyepiece parallel to the current movement of the right ascension axis.
  • Using the buttons on the hand control box, slew the telescope along the right ascension.
  • The eyepiece is rotated so that the guide star moves along the horizontal line of the crosshairs.
  • If the crosshair eyepiece has been successfully aligned, it must not be rotated again until the end of the Scheiner-method. [1]
Celestial points are inscribed as seen with the naked eye


Parallel alignment of the crosshair eyepiece to the celestial equator

(5a)
  • The guide star is viewed through the crosshair eyepiece over a period of about 10 minutes.
  • If the mount is turned too far to the East via the azimuth adjustment, the guide star in the eyepiece appears to move to the North. [4]
  • The azimuth adjustment is turned clockwise (yellow arrow) back in the direction of the meridian when viewed from above. [4]
  • After correction, wait a few minutes to see in which direction the star moves out of the image and correct accordingly. [3]
  • This process is repeated until the star no longer moves out of the image perpendicular to the tracking direction, but remains in the center along the horizontal line of the crosshair eyepiece. [3]
View through the crosshair eyepiece is upside down and laterally reversed

Drifting of the guide star towards North when the mount is adjusted too far to the East

Correction of the azimuth adjustment clockwise, if the mount is adjusted too far to the East [4]

(5b)
  • The guide star is viewed through the crosshair eyepiece over a period of about 10 minutes.
  • If the mount is turned too far to the west via the azimuth adjustment, the guide star will appear to move South in the eyepiece. [4]
  • The azimuth adjustment (viewed from above) is turned counterclockwise (yellow arrow) back in the direction of the meridian. [4]
  • After correction, wait a few minutes to see in which direction the star moves out of the image and correct accordingly. [3]
  • This process is repeated until the star no longer moves out of the image perpendicular to the tracking direction, but remains only in the center along the horizontal line of the crosshair eyepiece. [3]
View through the crosshair eyepiece is upside down and laterally reversed

Drifting of the guide star towards the South when the mount is adjusted too far to the West

Counterclockwise azimuth adjustment correction if the mount is adjusted too far to the West [4]

Sources:
[1] https://www.sternfreunde-muenster.de/pdf/andromeda20071.pdf
[2] https://openphdguiding.org/PHD2_Drift_Alignment.pdf
[3] https://www.nies.ch/doc/astro/scheiner.pdf
[4] Baader Planetarium GmbH

 

Correction of the pole height error

StepDescriptionIllustration
(1)
  • From the position that exists after correcting the azimuth error, the telescope is slewed West along the celestial equator.
  • Use the keys of the hand control box for this purpose

Approximate position of the telescope when looking for a star at the celestial equator in the West [1]
(2)
  • Select a suitable star in the range of 20° to 30° above the horizon and close to the celestial equator (+/-5°) [2]

Selection of a star 20° - 30° above the horizon and near the celestial equator
(3)
  • Due to the rotational movement over the right ascension axis, the crosshair eyepiece is tilted and must not be rotated.
Celestial points are inscribed as seen with the naked eye


Star centered in crosshair eyepiece

(4a)
  • The guide star is viewed through the crosshair eyepiece over a period of about 10 minutes.
  • If the mount is aligned too flat via the pole height adjustment, the guide star will appear to move north in the eyepiece. [3]
  • In this case, the telescope must be set steeper via the pole height adjustment. [3]
  • After correction, wait a few minutes to see in which direction the star moves out of the image and correct accordingly. [2]
  • This process is repeated until the star no longer moves out of the image perpendicular to the tracking direction, but remains only in the center along the East-West line of the crosshair eyepiece. [2]
View through the crosshair eyepiece is upside down and laterally reversed


Drifting of the guide star towards North when the mount is set too flat

Correction of the pole height adjustment if the mount is set too flat [3]

(4b)
  • The guide star is viewed through the crosshair eyepiece over a period of about 10 minutes.
  • If the mount is aligned too steeply via the pole height adjustment, the guide star in the eyepiece appears to move South. [3]
  • In this case, the telescope must be set flatter via the pole height adjustment. [3]
  • After correction, wait a few minutes to see in which direction the star moves out of the image and correct accordingly. [2]
  • This process is repeated until the star no longer moves out of the image perpendicular to the tracking direction, but remains only in the center along the East-West line of the crosshair eyepiece. [2]
View through the crosshair eyepiece is upside down and laterally reversed

Drifting of the guide star towards South when the mount is set too steep

Correction of the pole height adjustment if the mount is set too steep [3]

Sources:
[1] https://openphdguiding.org/PHD2_Drift_Alignment.pdf
[2] https://www.nies.ch/doc/astro/scheiner.pdf
[3] Baader Planetarium GmbH

 

If the telescope is not disassembled, at the end of a viewing phase the mount can be moved to the parking position via the hand control (if this has not already been stored via the hand control box), and the mount stores the alignment.
When dismounting the telescope, as little adjustment as possible should be made. Only one of the azimuth screws should be loosened. This way, hardly anything needs to be readjusted during the next observation