Dumpy level is the most commonly used instrument in leveling. In this level the telescope is restricted against movement in its horizontal plane and telescope is fixed to its support. A bubble tube is provided on the top of the telescope.
But however, the leveling head can be rotated in horizontal plane with the telescope. The telescope is internal focusing telescope is a metal tube contains four main parts as given below.
1. Objective lens
2. Negative lens
3. Diaphragm
4. Eye-piece
Objective Lens
Objective lens should be made as the combination of crown glass and flint glass. Because of this some defects like spherical aberration and chromatic aberration can be eliminated. A thin layer coating which has smaller refractive index than glass is provide on the objective lens to reduce the loss due to reflection.
Negative Lens
Negative lens located co axial to the objective lens. So, the optical axis for both lenses is same.
Diaphragm
Diaphragm is fitted inside the main tube which contains cross hairs (vertical and horizontal) and these are adjusted by capstan headed screws. The cross hairs are made of dark metal as filament wires which are inserted in diaphragm ring in exact position. For stadia leveling purpose, extra two horizontal cross hairs are provided above and below the horizontal wire.
Eyepiece
Eyepiece lens enable the ability to sight the object together with cross hairs. The image seen through eye piece is magnified and inverted. Some eyepieces erect the image into normal view and those are called as erecting eyepieces.