Patent GB-988145-A (GB)
Title: Optical means and microscope substage illuminating device incorporating the same
IPC: G02B21/08
Filed: 1961-04-26
Abstract: 988,145. Microscopes. J. BARABAS, K. LANG, and L. ZSELYONKA. April 26,1961 [May 4,1960], No. 15136/61. Heading G2J. A microscope sub-stage illuminating device comprises an elongated refracting body between two adjustable diaphragms, the body having a longitudinal section in the form of a pair of right trapezoids which are disposed in mirror arrangement with their equally long parallel sides in contact along the optical axis of the refracting body. The length of the longer parallel sides of the trapezoids is b = d(cot a + cot(# - #<SP>1</SP>)) where d is the height and α is the acute angle of the trapezoids, while # is the angle of incidence of light rays parallel to the optical axis of, and #<SP>1</SP> is the angle of refraction of such light rays in, said refracting body. As shown in Fig. 8, the refracting body 10 is mounted in a casing 45 which is displaceable by screws 47a at right angles to the optical axis of a sub-stage condenser consisting of lenses 22, 23 and a front lens 24a, 24b, these front lenses being mounted for pivotal movement so that either may be disposed in the operative position as the front condenser lens. Between the condenser lens 22 and the refracting body 10 is a diaphragm 21 which is adjustable by means of a rotatable sleeve 47 and in front of the body 10 is another diaphragm 20 which is adjustable by a rotatable sleeve 46 and is also transversely displaceable relative to the longitudinal axis of the body 10 by a screw 54. The body 10 serves to transpose the incident peripheral and central rays and by adjusting the diaphragm 20 a dark patch can be formed in the central part of the image formed, the size of this dark patch being inversely proportional to the size of the diaphragm opening. By adjusting the diaphragm 21 and keeping the diaphragm 20 fully opened the outer parts of the light beam can be excluded. In this way by operating both diaphragms an annular ring of light can be formed the width of this ring being adjusted to coincide with the phase ring used in the microscope. By transverse movement of the body 10 and/or of the diaphragm 20 a bright or dark patch of light can be formed eccentrically of the image centre. The refracting body can be made achromatic Fig. 1c by producing it from two members 10a, 10b of glasses having different dispersions and suitably selecting the radius of curvature of the cemented surface 10c. In another form the refracting body has the shape shown in Fig. 2. In order to allow of stereo illumination the front condenser lens 24b, Fig. 8, may have on its exit surface a filter layer consisting of polarizing filters 75, 76 Fig. 9 with their polarizing axes at right angles. Alternatively the filters 75,76 may be in complementary colours. In either case an opaque layer 77 covers the contact face of the two filters. Also in the embodiment of Fig. 8 there may be provided below the diaphragm 20 two semi-circular absorbing filters 78a, 78b, Fig. 10. These filters are mounted in carriers 79a, 79b the spacing between which can be adjusted. Any of the condenser lenses may be provided on their light entry faces with a filter layer Fig. 6, (not shown) consisting of absorbing portions separated by a transparent portion. The thickness of each absorbing portion increases from the centre to the periphery of the filter.