A compound microscope consists of three main parts: 1. Objective Lens 2. Eye Piece 3. Condensers.
Part # 1. Objective Lens:
The chief characteristics of the objective lens are:
(a) To gather the light rays coming any point to the object,
(b) To unite the light in a point of image,
(c) To magnify the image.
There are three types of objectives namely:
(a) Achromatic which are simplest in construction and adequate for most purpose,
(b) Flourite are those in which the aberrations are largely eliminated by use of these objectives, and
(c) Apochromatic which are most corrected with respect to aberrations.
Part # 2. Eye Piece:
The eye piece is also known as oculars.
The main functions of the eye piece are:
(a) To magnify the real image of the object formed by the objectives,
(b) To correct the defects of the objective.
There are three types of eye pieces namely:
(a) Huggenian eye piece in which two simple planoconvex lenses are employed, one of which is below the image plane. The convex surfaces of both layers face downwards. The huggenian eye piece works well with the low power achromats,
(b) Hyper-place eye piece are those which may be employed with the high power acromatic flourite and apochromatic objectives without introducing chromatic aberrations in the image; they give much flatter fields,
(c) Compensating eye piece consists of a chromatic triplet combination of lenses. These eye pieces are more perfectly corrected then the other two described above.
Part # 3. Condensers:
Several methods are employed for illustrating the object under examination.
In microbiology two methods are commonly used:
(a) Illumination by transmitted light, and
(b) Dark field illumination.
Condensers may be defined as a series of lenses for illumination to the object on the stage of microscope by transmitted light.