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The magnification of the telescope in tacheometer should be at least _______ to _______ diameters.
20 to 30
20 to 40
20 to 50
20 to 60
20 to 30
In tacheometry, the telescope of a tacheometer must possess higher magnifying power than a standard transit theodolite to clearly read staff graduations at long distances (up to 200โ300 meters). The required standard magnification ranges from 20 to 30 diameters. This high magnification provides a sharp, bright, and distinct view of the stadia wires against the levelling staff.
In tacheometry, the telescope of a tacheometer must possess higher magnifying power than a standard transit theodolite to clearly read staff graduations at long distances (up to 200โ300 meters). The required standard magnification ranges from 20 to 30 diameters. This high magnification provides a sharp, bright, and distinct view of the stadia wires against the levelling staff.
D=kโ s+c โ Distance equation in tacheometry
k=ifโ=100 โ Multiplying constant
c=f+d=0 โ Additive constant for anallatic lens
Tacheometric distance measurement relies on optical principles and reading stadia wire intercepts on a distant staff. High optical magnification enlarges the image of the staff graduations, reducing parallax and observation errors over extended sight lines. A larger objective aperture (typically 35 to 45 mm) accompanies this magnification to maintain high light intensity and image brightness.
The telescope magnification of a tacheometer must be at least 20 to 30 diameters.
The aperture diameter of the objective lens is typically kept between 35 mm and 45 mm (usually 40 mm).
An anallatic lens is fitted into the telescope to make the additive constant (c=f+d) equal to zero.
The multiplying constant (k=f/i) is usually fixed at 100 for simplicity of calculations.
Allows accurate reading of levelling staff at long distances without physical chaining.
High magnification power reduces parallax and manual observational errors.
Higher magnification reduces the overall field of view of the telescope.
Requires larger objective aperture to prevent image darkening at higher optical powers.
Preparation of topographic maps in rough or hilly terrains where chaining is difficult.
Location surveys for roads, railways, and reservoirs.
Standard specifications of a tacheometer state that magnification must lie between 20 to 30 diameters.
Option B (20 to 40), Option C (20 to 50), and Option D (20 to 60) exceed standard field specifications and reduce field-of-view excessively without operational benefits.
A is correct โ The required magnification power for a tacheometer telescope is defined as 20 to 30 diameters to ensure clear staff readings at long distances.
Remember that while k=100 and c=0 are the standard instrumental constants, the optical specs require magnification = 20โ30 diameters and aperture = 35โ45 mm.