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Parallax can be elimiated by focusing on the_____
eye piece
Objective glass.
Both A and B
None of the above
Both A and B
Parallax in a surveying telescope occurs when the image formed by the objective lens does not lie exactly in the plane of the crosshairs. Eliminating parallax requires two independent focusing operations: first focusing the eyepiece to bring the crosshairs into sharp focus, then focusing the objective lens to ensure the image of the object coincides with the plane of the crosshairs.
Parallax in a surveying telescope occurs when the image formed by the objective lens does not lie exactly in the plane of the crosshairs. Eliminating parallax requires two independent focusing operations: first focusing the eyepiece to bring the crosshairs into sharp focus, then focusing the objective lens to ensure the image of the object coincides with the plane of the crosshairs.
f1тАЛ=v1тАЛтИТu1тАЛ тАФ The Lens formula governing objective focusing where f is focal length, v is image distance, and u is object distance.
The principle relies on bringing two distinct focal planes into coincidence. When the eyepiece is adjusted, the crosshairs appear sharp to the observer. When the objective lens is adjusted, the light rays from the distant object are brought to converge exactly on the reticle plane, ensuring that any lateral shift of the eye does not cause the image to appear to move relative to the crosshairs.
Parallax is a common error in surveying instruments like Theodolites and Dumpy Levels.
It is observed by moving the eye slightly to the side while looking through the eyepiece.
If the image appears to shift relative to the crosshairs, parallax is present.
The adjustment must be performed every time the distance to the observed object changes.
Ensures precise sighting for accurate angular measurements.
Eliminates observational errors caused by eye movement.
Requires time-consuming re-focusing when changing targets at different distances.
Levelling operations in Civil Engineering.
Theodolite traverse surveying.
Tacheometric surveying.
When focusing the eyepiece, point the telescope toward a bright, uniform background to see the crosshairs clearly.
Option A (Eyepiece) only fixes the clarity of the reticle, while Option B (Objective) brings the external scene into the plane of the reticle; both are mandatory for complete parallax elimination.
C is correct тАФ Parallax is eliminated by performing both eyepiece focusing for the reticle and objective focusing for the target image.
Always remember that eyepiece focusing is dependent on the observer's eyesight, whereas objective focusing is dependent on the object's distance from the telescope.
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