in a telescope, microscope, or other optical instrument, the lens or lenses nearest the viewer's eye
The lens or lens group closest to the eye in an optical instrument; an ocular. Also called eyeglass .
- For the eyepiece the other rule holds; the object is represented by narrow pencils, and it is hence possible to subject the relatively great object, viz.
- This change is usually effected by mounting the objective and eyepiece on two telescoping tubes, so that by drawing apart or pushing in the tube length is increased or diminished at will.
- If we assume that a normal eye observes the image through the eyepiece, the eyepiece must project a distant image from the real image produced by the objective.
- In this case the optical tube length equals the distance of the adjacent focal planes of the two systems, which equals the distance of the image-side focus of the objective F 1 ' from the object-side focus of the eyepiece F2.
- The image viewed through the eyepiece appears then to the observer under the angle w", and as with the single microscope tan w" = I /f 2 ' (4) where f' 2 is the image-side focal length of the eyepiece.