An Easily Used Ultra-Violet Microscope Objective

Abstract

THE ultra-violet microscope is a useful cytochemical tool because it enables one to locate and measure the amounts of absorbing substances in cells (see, for example, Caspersson¹). It is a considerable advantage if the microscope objective is achromatic throughout the visible and ultra-violet regions of the spectrum; focusing of the microscope in visible light is then simplified, and many wave-lengths may be used simultaneously in order to obtain an absorption curve. Reflecting microscopes are completely achromatic, and hence have been much favoured for cytochemical use (cf. refs. 2 and 3, for example). After several years of use of reflecting objectives, we find they have three main disadvantages: (a) the numerical aperture at present possible, ≃ 0.65, is rather low for many purposes; (b) the ultra-violet reflectivity of front-surface mirrors sometimes deteriorates rapidly; (c) very exact positioning of the mirrors relative to each other is necessary. If the mirrors are preset during manufacture, dislocation may take place in use, thus necessitating return to the maker; if, however, the objective is adjustable, some users may have trouble in making the adjustments. In this communication we describe a simple objective which has been designed to overcome all these disadvantages.