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United'states' Patent 0 3,690,908 United’States' Patent 0 ice Patented Sept. 12, 1972 1 2 SUMMARY OF THE INVENTION 3,690,908 HIGH INDEX OPTICAL GLASS An object of the invention is to provide an optical Edgar J. Greco and Gerald E. Blair, Rochester, N.Y., glass having a high index of refraction and low absorp and Guy E. Rindone, State College, Pa., assignors to tion in the visible region of the spectrum. Eastman Kodak Company, Rochester, NY. Another object of the invention is to provide a low No Drawing. Filed Oct. 1, 1970, Ser. No. 77,330 Int. Cl. C03c 3/30, 3/02, 3/12 color, highly refractive optical glass from ‘which camera U.S. Cl. 106—47 Q 3 Claims lens components can be practicably made. An additional object is to provide an optical glass hav 10 ing a high index of refraction and a low dispersion. ABSTRACT OF THE DISCLOSURE A further object is to provide an optical glass of the foregoing types which can be manufactured under normal An optical glass having a high index of refraction and glass making conditions. Other objects will become ap low absorption in the visible region of the spectrum con parent from the description to follow and from the ap tains as components tellurium dioxide, lanthanum oxide, 15 pended claims. boron oxide, potassium oxide, tantalum pentoxide, and The invention achieves the foregoing objects by the germanium dioxide. provision of optical glasses consisting essentially of com ponents in the following range of percentages by weight: BACKGROUND OF THE INVENTION 20 Component: Weight percent Tellurium dioxide (TeO2) _____________ .. 60-85 Field of the invention Lanthanum oxide (M1203) ____________ __ 5-35 This invention relates to optical glasses, and in par Aluminum oxide (Al2O3) ______________ __ 0-5 ticular to optical glasses having high indices of refraction Boron oxide (B203) __________________ __ 0-5 and high transparency. 25 Potassium oxide (K20) _______________ __ 0-5 Zinc ?uoride (ZnF2) __________________ _.. 0-5 Description of the prior art Tantalum pentoxide (Ta2O5) ________ ._.. up to 10 Germanium dioxide (G603) ________ _._ up to 5 The quality of optical systems such as those used in photography is substantially enhanced by the incorpora 30 DETAILED DESCRIPTION OF PREFERRED tion of lens components having high refractive indices, EMBODIMENTS OF THE INVENTION exceeding for example 2.00, but the necessity that these components have very low color, i.e. low absorption in .The present invention provides optical glasses ex the visible region of the spectrum, has impeded the de tremely well suited for lens systems of the type used in cameras. The glasses have very high indices of refraction velopment of such glasses. For example, US. Patent 35 3,291,620 discloses an optical glass having an index of (2.00 and greater), and low dispersions for these indices refraction exceeding 2.00, but that glass has a WCI‘Y high (Abbé numbers greater than 19.0). These glasses have blue absorption which severely limits the use of that glass been found to absorb no red or green in the visible region for photographic purposes. This blue absorption gives the of the spectrum, and to absorb signi?cantly less blue in glass a yellow-green color and has been attributed to the 40 this region than other optical glasses having high refrac presence of tungsten oxide in the glass. Tungsten oxide tive indices, as indicated by the high transparency there improves the chemical stability of the glass, but hampers of. Therefore, the present glasses have the capacity to its usefulness as a lens material. The glass disclosed in transmit substantially more light than previously known the cited patent has additionally been found to have an optical glasses having similar refracting characteristics. undesirably high absorption in the red region of the spec 45 Optical glasses have been developed according to the trum. Other optical glasses are known having similarly invention which have yielded glasses satisfying the criteria high refractive indices but those glasses have excessive of low color and high refractive index particularly well; absorptions of both blue and green in the visible region these glasses have weight compositions within the fol of the spectrum. lowing ranges which fall within the aforementioned ranges Optical glasses having low color as well as high re 50 of values: ?ractive indices ?nd particular utility in cameras because their transmission characteristics reduce the minimum Component: Weight percent light level at which highly sensitive photographic ?lm: can TeOz 62.1-84.5 be satisfactorily exposed in a camera. Thus, the level of ambient illumination of which such exposures can be 55 La2O3A1203 0.0-1 .1 made would be reduced with a colorless lens, making B203 __ 0.0-1.3 resort to arti?cial lighting devices less frequent for the K20 __ 0.0-0.9 photographer. Such glasses have heretofore not been ZnFz 0.0-0.5 available to designers of optical systems for cameras. Ta2O5 2.8-7.4 Moreover, present glasses having high indices of refrac 60 G‘eOz 2.1-4.1 tion have Abbé numbers (i.e. reciprocal dispersive powers) which are relatively low, whereas high Abbé numbers These glasses have refractive indices ranging from 2.00 are desired in optical glasses (the glass disclosed in the to 2.12. They may be ?red in gold crucibles at tempera above-cited patent allegedly has an Abbé number range tures of approximately 900° C. of 16.5-17.5). 65 One example of a glass according to the invention 3,690,908 3 has an index of refraction of 2.10, an Abbé number of Boron oxide (B203) ______________ __ 0.0-1.3 19.4, and a weight composition as follows: . Potassium oxide (K20) ____________ _- 0.0-0.9 Component: Weight percent Zinc ?uoride (ZnFz) ______________ __ 0.0-0.5 TeOa 83.2 Tantalum pentoxide (Ta2O5) ________ -__ 2.8-7.4 Lagos 8.4 Germanium dioxide (GeO2) ________ __ 2.1-4.1 A1203 ________________________________ __ 0.9 2. An optical glass having the weight composition: B203 0.6 Component: Weight percent K20 0.3 Tellurium dioxide (TeO2) ______________ .__ 83.2 T3205 3.2 10 Lanthanum oxide (Lagos) ______________ _. 8.4 GeO-z 3.4 Aluminum oxide (A1203) _______________ .... 0.9 It has been found that in the production of large scale Boron oxide (B203) ____________________ __ 0.6 melts (on the order of 8,000 grams), a more homogeneous Potassium oxide (K20) ________________ __ 0.3 glass can be produced if the aluminum oxide (A1203) Tantalum pentoxide (Ta2O5) ____________ __ 3.2 is eliminated. A glass of the following weight composition 15 Germanium dioxide (Geog) ____________ .__ 3.4 has been made accordingly: 3. An optical glass having the weight composition: Component: Weight percent Component: Weight percent TeOB __ 83.4 - Tellurium dioxide (TeOZ) _______ __'_ ____ __ 83.4 143203 8 .5 20 Lanthanum oxide (Lagos) ______________ .__ 8.5 B203 _.. 1.2 Boron oxide (B203) ____________________ .. 1.2 K20 .. 0.3 Potassium oxide (K20) ________________ .__ 0.3 T3205 3 .2 Tantalum pentoxide (T8405) ____________ __ 3.2 GeOz 3 .4 Germanium dioxide (GeOz) ____________ _._ 3.4 The preceding glass has a refractive index of 2.10 and an 25 Abbe number of 19.4. References Cited The invention has been described in detail with par UNITED STATES PATENTS ticular reference to a preferred embodiment thereof, but it will be understood that variations and modi?cations 2,763,559 9/1956 Weissenberg et a1. __ 106-47 R 3,291,620 12/1966 Evstropjev et a1. -__- 106—47 Q can be elfected within the spirit and scope of the inven 30 tion. FOREIGN PATENTS We claim: .1. Optical glasses having a refractive index in the 202,491 11/1967 U.S.S.R. __________ 106-47 Q range ?rom 2.00 to 2.12 and an Abbé number greater than 19.0, said glasses consisting essentially of com- 3 OTHER REFERENCES ponents having a weight composition within the follow llmaoka, M.: Glass-Formation Range and Glass Struc ing ranges: ture, in Advances in Glass Technology, Plenum Press, Component: Weight percent N.Y., 1962, pp. 149-153. Tellurium dioxide (TeO2) __________ __ 62.1-84.5 TOBIAS E. LEVOW, Primary Examiner Lanthanum oxide (LazO3) __________ .__ 6.3-31.4 40 Aluminum oxide (A1203) __________ __ 0.0-1.1 M. L. BELL, Assistant Examiner .
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