. Beck microscopes. Microscopes. Fis- 4. When this illuminator is used on slides varying from 1 m/m. to T| m/m. the cone of light which it transmits to the object is between 1 and 1-4 , which enables any object glass with an aperture not higher than -95 to be employed with it. If, however, a slide is used that is not thicker than ^ m/m., when the illuminator is focussed for this thickness the angle of the cone of light is altered so that its angle is between 1-25 and 1-4 , and an object glass with an aperture of T2 can then be employed. We make a 2 m/m. and 'i m/m.
. Beck microscopes. Microscopes. Fis- 4. When this illuminator is used on slides varying from 1 m/m. to T| m/m. the cone of light which it transmits to the object is between 1 and 1-4 , which enables any object glass with an aperture not higher than -95 to be employed with it. If, however, a slide is used that is not thicker than ^ m/m., when the illuminator is focussed for this thickness the angle of the cone of light is altered so that its angle is between 1-25 and 1-4 , and an object glass with an aperture of T2 can then be employed. We make a 2 m/m. and 'i m/m. both in the achromatic and apochromatic series, which while being equally useful for ordinary work is specially made for dark ground illumination. The front lens of the illuminator can be unscrewed and then forms an excel- lent dark ground illuminator, which can be used dry and not in immersion the slide, with low powers whose angle does not exceed -7 The substage fitting regularly supplied is made to the standard size l'52in. but special fittings can be supplied to suit other sizes at a small extra cost. In ordering for microscopes not of our manufacture this size should be given and also the distance from the bottom of the substage fitting when it is focussed as far up as possible to the top of the stage, so that the illuminator may be supplied of the correct No. 3296. High power dark ground immersion illuminator, in plain substage fittng No. 3297. Ditto, in centring substage fitting This illuminator throws upon the object a hollow cone of light between 1 and It must be used in immersion contact with the slide and the slide must be 1 m/m. thick or the light will not be in focus. It is specially intended for use with object glasses of high power, as it gives a very small but brilliantly illuminated spot of light. Oil immersion object glasses such as the 3 m/m. with an aperture of .95 can be used with it, but lenses with a greater aperture require to be s
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