COMPOUND MICROSCOPE CONDENSER

MAKER:R. & J. Beck Ltd

MODEL:PATENT FOCUSING DARK GROUND IMMERSION ILLUMINATOR

c.1900

The Beck Patent Focussing Dark Ground Immersion Illuminator n.a. 1.25 – 1.45 rated for slides of 0.04 inch(1 mm) thickness. It is signed R & J. BECK. L^TD, .02 SLIP N.A. 1.33-1.45.

The focusing feature, illustrated by the images to the left, allowed for variation in slide thickness. According to the Beck Catalog, although rated for a 1 mm slide thickness, the focusing adjustment allows it to be used with slides 1/2 mm to 1.5 mm thick. When the condenser is adjusted so that the bottom lens is closer to the top, the thicker the slide it will work with and when the bottom element is further away from the top, the thinner the slide that can be used; this is particularly useful for permanent slides mounted in the past, which varied in thickness. It is stated in a 1930s Beck catalog that when the top element is removed this condenser is a good dry darkfield condenser for low power objectives provided the N.A. does not exceed 0.7, but this example does not have a removeable top element. The basic form of this device was described in Conrad Beck's 1921 The Microscope, a Simple Handbook. It was also described in Gage's THE MICROSCOPE, AN INTRODUCTION TO MICROSCOPIC METHODS AND HISTOLOGY, DARK-FIELD EDTIION. (14TH REVISED) of 1925, p436-. The focusing mechanism was originally controlled by a lever; this later version has the focusing controlled by the large knurled disk. It is designed on the cardioid principal, which is still used for dark ground illumination today.