The rays of light from an infinitely distant point source are parallel and can be focused with the accommodation muscles of the eye entirely relaxed. The fast ray or fast component for a crystal or fiber corresponds to the lower refractive index. The area of the object that is seen when the image is observed. It may range in diameter from several millimeters to less than 0.1 mm. The magnification and the size of the diaphram opening in the eyepiece governs the diameter of the field of view.
Penetration is a synonym.
In a photomicrographic system particularly, an iris diaphram that is imaged in the field of view with Kohler illumination. This limits the extent of the illuminated field and eliminates much extraneous light. See diaphram . The iris diaphram that is located in front of the collecting lens of the light source. With Koehler illumination, the condenser focuses the image of the field diaphram onto the image plane.