Use of a Prismatic Binocular for Viewing Near Objects

Abstract

A FEW years ago, with a view to the observation of close objects out of doors, I procured some glass adapter lenses for use on the object glass of the half of a prism binocular (× 12) which I carried about with me. Finding, however, that this method involved the use of several glass adapters, and that with it I had to know the exact distance of my objective, I prevailed on an optician—after lengthy argument, he deeming the experiment impracticable—to remove the eyepiece and refit it for use with a long screw thread. The result was most satisfactory; by this device I can draw out the eyepiece and adjust it to the proper distance for any observation down to four feet off. This device is also very useful for indoor work, such as observation on the occupants of an aquarium.