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THE POWELL & LEALAND No 1

MAKER: POWELL & LEALAND

DATED: 1874

SIGNED ON THE ARM: Powell & Lealand, 170 Euston Road, London and also dated 1874

STAGE-CENTERING ADJUSTMENT SCREWS

Authors: Jurriaan de Groot & Barry Sobel

Editor: Joseph Zeligs

The Powell & Lealand No. 1 microscope has a rotating stage. In order for this to function well the axis of rotation must be centered in the optical axis. To do this, P & L provided a complex group of screws acting on the stage from the back of the limb. These are shown in the image, taken with the microscope upside down.

Powell & Lealand No 1 microscope

There are three main adjustment screws. After loosening the four stage-locking screws on the bottom, the three centering screws can be used to center the stage. The middle screw adjusts the forward-backward position, but the adjustment is not sprung so the stage needs to be pushed back manually as this screw is loosened. The screws on either side of the central screw, when used individually, each act to adjust right or left movement, each acting in an arc, the middle screw acting as a fulcrum. This adjustment was most likely made at the factory and not intended to be changed by the user, as it is quite tedious to use, and the locking screws are quite beefy, not to mention in an inconvenient location. The two smaller screws above the center screw in this image are not part of the centration adjustment mechanism.