Collimating eyepiece
an eyepiece with a diagonal reflector for illumination, used to determine the error of collimation in a transit instrument by observing the image of a cross wire reflected from mercury, and comparing its position in the field with that of the same wire seen directly. | |
See under Collimate. |
Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.