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摘要

I am sure many readers will want to make Dick Stephen's centring microscope (Issue 106). It can be used not only as a centring microscope but, with suitable illumination on a milling machine, as a poor man's toolroom microscope when forming small but complex shapes. Those who buy the Hemingway kit will no doubt get all the correct optics, but those who attempt to buy the items separately for themselves may make expensive purchasing errors. Starting at the sharp end, a new 40 mm focal length microscope object may be not only hard to find but also very expensive. In this application, any achromatic lens of 40 mm focal length will do. To turn the light rays through 90 degrees a prism silvered on its hypotenuse is specified. This is a relatively expensive solution and a piece of front surface mirror about 10 by 16 by 3 mm thick would do just as well. A front surface.? mirror is silvered on the front and you can tell which is the front by touching it with a finger nail, when the nail and its reflected image will touch without a thickness of glass between them. Next least expensive is a plain prism which will need to be rotated through 180 degrees to that shown in the GA drawing, so that the light enters through one 90 degree face, is internally reflected off the hypotenuse face and