Correct Answer - Option 2 : Convex lens
Explanation:
Tacheometer:
(i) This is another method of surveying wherein the horizontal distance and the difference in elevations are determined indirectly by an instrument called as tacheometer.
(ii) Tacheometer is nothing but a transit theodolite fitted with a stadia diaphragm.
(iii) The stadia diaphragm generally consists of two stadia hairs, one above and one below and equidistant from central horizontal hair.
Major Characteristics of a Tacheometer:
(i) The multiplying constant (k) of the tacheometer is usually a round figure and mostly it is 100.
(ii) The additive constant (C) of the tacheometer is kept very small and mostly it is kept zero.
(iii) An additional convex lens is provided between eyepiece and object glass at a fixed distance and known as anallactic lense to make additive constant zero.
(iv) The magnifying power of the eyepiece is kept high to make the staff graduations clearly visible even at a large distance.
(v) The aperture of the objective is kept usually 35 mm to 45 mm to make the image sharp.
