Parts of the Instrument and Levelling Head
Adjusting the levelling head
Aim - to level the tribrach so that the telescope rotates in a horizontal plane.
Levelling an instrument with a spherical spirit level.
Align
the telescope parallel to two foot screws.
Facing the instrument rotate both foot screws in opposite directions at the same time. Either thumbs moving inwards or thumbs moving outwards.
The bubble moves in the direction of the left thumb.
When
the bubble has settled opposite the centre mark the instrument is level
on this axis.
The bubble will probably be against the side of the circular spirit level, and needs moving in to the centre.
The
first two screws are level so they must not be touched.
Using the left hand adjust the third levelling screw to centre the bubble. Again the bubble will move in the same direction as the left thumb.
With
the bubble centred the instrument should be level.
As a check rotate the instrument through 90°. If necessary re-level the original two foot screws and repeat the rotation to check the third one.
The tube is engraved with a calibration circle to show the centre. The bubble must remain within this circle for the compensator to work.
Now check your knowledge:
