DE1175457B - Lens with an aperture ratio greater than f / 1 - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Boarding school Class: G 02 b

German class: 42 h -4/06

Number: 1175 457

File number: N 16496IX a / 42 h

Filing date: April 2, 1959

Opening day: August 6, 1964

The invention relates to an objective with an aperture ratio greater than // 1 for photography, Image throw, etc., consisting of the following four members in the order of the longer one Back focal length:

a) a collecting foremost link;

b) a collecting, meniscus-shaped, forward convex second limb, which consists of a collecting and a diffusing lens;

c) a dispersing, also meniscus-shaped, * ° forward convex third member, which consists of a collecting and a dispersing lens, whose axial thickness is at least 0.35 / (/ = total focal length of the lens) and whose The converging lens consists of glass with an average * 5 refractive index that is at least 0.04 lower than that of the glass of the diverging lens;

d) one, consisting of a diffusing and a converging lens, a convex front surface having collecting fourth member, the rear surface of which has a radius of curvature of has at least 2 / and its axial thickness is at least 0.3 /.

A lens built according to the above conditions is already known in which a good correction with an extremely large aperture ratio (// 0.74) is obtained, among other things, by using the foremost collecting element and glasses with extremely high refractive indices for the collecting lens of the second element and relatively low dispersions, especially glasses containing rare earth oxides. In the known lens, glasses with mean refractive indices of na = 1.717 and 1.691 and Abbe's numbers of ν = 47.9 and 54.8 are used for the lens elements in question. The well-known lens has a negative focal length and is therefore only intended for imaging close objects.

It is known that glasses of this type are relatively difficult to manufacture and only in small ones Quantities per melt can be obtained. As a result, these glasses can only be sliced up to now of limited dimensions, the price of which is much higher than that of the usual ones Types of glass. In general, the higher the required refractive index, the greater the effect of these disadvantages is. They then form a very serious restriction on the application of the previous one System in the form of a lens with a large aperture and a large focal length, e.g. B. more than 10 cm.

The aim of the present invention is to provide a lens of the specified type with a lens with an aperture ratio larger
as f / 1

Applicant:

N. V. Optical industry "De Oude Delft",

Delft (Netherlands)

Representative:

Dr.-Ing. E. Hoffmann, patent attorney,

Munich 8, Maria-Theresia-Str. 6th

Named as inventor:
Johannes Becker, Delft,
Henricus Wilhelmus Bulthuis,
The Hague (Netherlands)

Claimed priority:

Netherlands of April 3, 1958 (226 601)

good correction for all aberrations in a flat field of view, without the use of such glasses for the elements with the largest dimensions, in particular the foremost link and the converging lens of the second link, what restrictions on the possible focal length of the lens or of its price.

It is true that a highly opened lens (JIX) with a somewhat modified design has already become known, in which only relatively low-refractive glasses (n ^ <1.62) have also been used. However, the state of correction of this lens is very poor compared to the first-mentioned known lens.

The lens according to the present invention is characterized in that the foremost link is a forward convex, meniscus-shaped single lens made of glass with a refractive index less than 1.65, the axial thickness of which is less than 0.2 /, the front surface of which is a Radius of curvature between / and 2.2 / and the rear surface of which has a radius of curvature between 10 / and infinite that furthermore the glass of the converging lens of the second member has a refractive index below 1.675 which is at least 0.02 and at most 0.04 lower than the refractive index of the glass of the diverging lens this second link, and that the radius of curvature of the interface between the two lenses of the second link between 1.5 / and 3 /.

«9 639/185

Two embodiments of the objective according to the invention are shown in the drawing for explanation shown.

F i g. 1 represents an objective with an aperture ratio of // 0.7 and a field angle of 15 °, that is corrected for an infinite object distance;

F i g. 2 shows an objective which is also corrected for infinity and a somewhat smaller focal ratio has (// 0.75) with a larger usable field angle of 21 °.

The data of the in F i g. The systems shown in FIGS. 1 and 2 are summarized in Tables I and II, respectively. the The marks used can also be found in the drawing. The total focal length of the systems is refer to 100. Table I.

// 0.7

Field 15 ° / = 100 F i g. 1

= 195.31 = 176.74 Back focal length 4.3 Table II / = 100 Abbe 35 Middle Field 21 ° 4.0 Counting
V = 24.5675 = 1310.21 Surfaces
distances Refractive
indices (n _d ) Back focal length Middle = 101.65 Refractive
indices (n _d ) 46.5 Radii of curvature = 102.40 d _l = 16.20 1.5827 Surfaces
distances = -249.64 1.5831 - = -234.52 d ₂ = 1.5 - d _n = 15.14 30th = 193.75 A IC 58.5 = 199.70 d ₃ = 34.10 1.6516 "12 - U-> 1.6385 = 50.96 d _ls = 32.0 31.2 = 51.28 d _t = 2.6 1.6889 1.6668 ^r i = 190.80 du = 2.5 - = 204.29 = 23.31 d _h = 0.4 - 35 / ·. d _ls = 0.5 58.5 = 22.39 = 59.89 d _t = 34.5 1.6516 1.6385 d _u = 31.5 27.8 = 53.08 = 22.73 d ₇ = 13.6 1.7482 1.7215 ] · d ₁₇ = 14.0 - = 22.73 = -602.5 d ₈ = 11.8 die = 11.9 ^r s 1.5633 50.8 4 ° = -332.57 = Infinite d ₉ = 6.2 1.5633 d ₁₉ = 6.6 1.7340 50.9 // 0.75 d ₁₀ = 29.4 1.7340 dta = 13.7 45 1.7340 d ₂₁ = 20.8 Fig. 2 ^r n Radii of curvature 50 ^ 12 Abbe Counting
V 59.3 55 ^r lo 55.5 33.1 * ι ~. 6o / · ,. 55.5 f 29.3 γ ⁵ 50.8 ^ 22 50.9 f - 41.0

For the foremost link in FIG. 1 a glass with an average refractive index na = 1.5827 and an Abbe's number of 46.5 is used, whereas the converging lens of the second element is made from a glass with an average refractive index of na - 1.6516 and an Abbe's number of 58, 5 exists. It should be noted that the latter glass, which is also used for the converging lens of the third link, although it is a lanthanum crown glass and thus belongs to the class of glasses made from rare earth oxides, has a relatively low refractive index and is one Price can be obtained which is only slightly higher than that of the usual barium crown glasses.

In the example of FIG. 2 glasses with refractive indices of nd = 1.5831 and 1.6385 and Abbe's numbers of 59.3 and 55.5 are used for the foremost lens and for the converging lens of the second member. These are also barium crown glasses, which can be obtained in sufficiently large pieces at moderate prices. It should be noted that the collecting part of the rearmost link in this example consists of two lenses with a slightly curved, cemented separating surface which is concave towards the front. This putty surface improves the chromatic correction somewhat. It also enables the use of a rearmost lens made of a glass with a refractive index of na = 1.7340 and an Abbe number of 41.0, instead of the glass with na = 1.7340 and ν - 50.9 in the first example. The latter glass is somewhat radioactive due to its thorium content and can cause fogging of the film in the focal plane when the lens is used for photographic purposes. Because the two rear lenses have the same refractive index, the interface in no way affects the monochromatic correction.

Claims (3)

Patent claims: 1. Lens with an aperture ratio larger as // 1 for photographic image throw and the like, consisting of the following four elements in the order from the longer back focal length: a) a collecting foremost link; b) a collecting, meniscus-shaped, forwardly convex second limb consisting of a a collecting lens and a diffusing lens; c) a dispersing, also meniscus-shaped, forward convex third phalanx, the consists of a converging and a diverging lens, the axial thickness of which is at least 0.35 / (/ = total focal length of the lens) and its converging lens made of glass exists whose mean refractive index is at least 0.04 lower than that of the Divergent lens glass; d) one, consisting of a diffusing and a converging lens, a convex one Front surface having collecting fourth member, the rear surface of which has a radius of curvature of at least 2 / and whose axial thickness is at least 0.3 /, characterized in that the foremost Link a forward convex, meniscus-shaped single lens made of glass with a smaller refractive index than 1.65, the axial thickness of which is less than 0.2 /, the front surface of which has a radius of curvature between / and 2.2 / and the rear surface of which has a radius of curvature between 10 / and infinity that furthermore, the glass of the converging lens of the second member has an index of refraction below 1.675 by at least 0.02 and at most 0.04 lower than the refractive index of the glass of the diverging lens second member, and that the radius of curvature of the interface between the two lenses of the second link is between 1.5 / and 3 /. 2. Lens according to claim 1 with a total focal length of / = 100, characterized by the following data, being for the refractive power of the refracting surface deviations of ± 0.2 / '/ and for the axial thicknesses and distances Deviations of ± 0.05 / are possible: Radii of curvature Axial thickness or
distance Mean refractive index (n _rf ) Abbe number = 195.31 = 2456.75 = 102.40 = -234.52 = 199.70 = 51.28 = 204.29 d _x = 16.20 1.5827 d ₂ = 1.5 - d ₃ = 34.10 1.6516 d _t = 2.6 1.6889 fk = 0.4 - r ₈ = 22.39
ho = 53.08
= 22.73
= -332.57 = 34.5 1.6516 d ₇ = 13.6 1.7482 d _s = 11.8 - d ₉ = 6.2
d ₁₀ = 29.4 1.5633 1.7340 46.5 58.5 31.2 58.5 27.8 50.8 50.9 3. Lens according to claim 2 with a total focal length of / = 100, characterized by the following data, being for the refractive power I j of the refracting surfaces deviations of ± 0.2 // and for the axial thicknesses and distances Deviations of ± 0.05 / are possible: Radii of curvature Axial thickness or distance Mean refractive index (n _d ) Abbe number r _lt = 176.74 r ₁₃ = 1310.21 r ₁₄ = 101.65 4i = ^ 12 = dis = r _M = r ₁₇ = r _ls = 193.75 50.96 190.80 ⁼ 23.31 d ₁₇ = </. «= r ₂₀ = 59.89 r "= 22.73 r _i2 = -602.5 r ₂₃ = infinite 15.14 1.5831 j 5 32.0 1.6385 2.5 1.6668 0.5 - 31.5 14.0 11.9 6.6 13.7 20.8 1.6385 1.7215 1.5633 1.7340 1.7340 59.3 55.5 33.1 55.5 29.3 50.8 50.9 41.0 References considered: British Patent No. 696,902; French Patent No. 1,012,507; Swiss patent specification No. 196 705. 1 sheet of drawings 409 639/185 7.64 © Bundesdruckerei Berlin