Join 60,000+ competitive exam aspirants
or with email
Your Cart
Subtotal₹0
Total₹0
Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
Join 60,000+ competitive exam aspirants
Which line is passing through the intersection of the cross hair of the diaphragm and the optical center of the objective?
Line of axis
Vertical axis
Axis of bubble
None of the above
Line of axis
The 'Line of Collimation' (often referred to as the Line of Sight) is defined as the imaginary line passing through the intersection of the crosshairs in the diaphragm and the optical center of the objective lens. It is the fundamental reference line for establishing horizontal and vertical measurements in surveying instruments like the theodolite and dumpy level.
The 'Line of Collimation' (often referred to as the Line of Sight) is defined as the imaginary line passing through the intersection of the crosshairs in the diaphragm and the optical center of the objective lens. It is the fundamental reference line for establishing horizontal and vertical measurements in surveying instruments like the theodolite and dumpy level.
Lcol=f(C,O) — where C is the diaphragm crosshair intersection and O is the objective optical center.
The optical system of a surveying instrument aligns the mechanical center of the eyepiece crosshairs with the physical center of the objective lens. This alignment ensures that when a surveyor sights an object, the visual ray follows a straight geometric path, facilitating precise horizontal and vertical angle measurement without parallax error.
The Line of Collimation is also known as the Line of Sight.
It must be perpendicular to the horizontal axis of the instrument for accurate measurements.
Errors in this alignment are known as collimation errors.
The diaphragm carries the crosshairs (horizontal and vertical wires).
Ensures precise alignment of the optical axis.
Provides a consistent reference for angular observations.
Prone to errors if the diaphragm is shifted or the objective lens is loose.
Requires periodic calibration (Two-peg test) to ensure horizontality.
Levelling and profile surveying.
Theodolite traversing and angular measurement.
Tacheometric surveying.
The Line of Collimation is distinct from the 'Axis of the Bubble Tube', which is the line tangent to the longitudinal curve of the bubble tube at its center.
Option B (Vertical axis) is the axis about which the theodolite rotates horizontally.
Option C (Axis of bubble) is used for leveling the instrument, not for the optical sight line.
A is correct — The line of collimation is the visual axis established by the intersection of the diaphragm crosshairs and the optical center of the objective.
Remember that the 'Line of Collimation' refers to the sight path, whereas the 'Vertical Axis' refers to the instrument's axis of rotation; confusing these is a common cause of error in competitive exams.