The line of sight of the telescope of a surveying instrument, defined as the line through the rear nodal point of the objective lens of the telescope and the center of the reticle when they are in perfect alignment. In levelling, a method of calculating reduced levels by subtracting staff readings from the level of the line of sight (collimation line) of the instrument. This method is usually favoured where it is required to obtain the levels of many points from one set-up.
Line of sight: It is the imaginary line passing through the intersection of the crosshair on the diaphragm and the optical center of the objective lens. when a line of sight comes in a horizontal plane, it is called a line of collimation.
Temporary Adjustments of A Level
The adjustments to be made at every setting of the instrument are called temporary adjustments. The following three adjustments are required for the instrument whenever set over a new point before taking a reading: (i) Setting (ii) Levelling and (iii) Focusing.
Permanent adjustment of auto level-------
There are three permanent adjustments viz.:
The line of collimation should coincide with the axis of the telescope.
The line of collimation should be parallel to the axis of the bubble tube.
The axis of the bubble tube should be perpendicular to the vertical axis.
Негізгі бет Auto level || Line of Collimation || Line of sight || Temporary & Permanent Adjustment of Auto level
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