DE1797285C - Five-lens, four-part lens - Google Patents

Description

The invention relates to a five-line, four-element telephoto lens for photographic purposes, which has an aperture ratio of at least 1: 2.8 and whose focal length is greater than the distance of the object-side front lens vertex from the image plane and between 4 to 5 times that to be marked Image format diagonal lies. The one on the side of the longer radiation range, in its overall effect positive system part includes a standing as a front lens planoconvex lens and a negative meniscus, the has an axial center thickness of at least 0.15 the focal length of the lens and which is in the form of a cemented member composed of a biconvex converging lens and a biconcave diverging lens, In the case of the meniscus and the front lens, turn their curvatures towards the object. The one on the side of the The system part, which is also positive, is followed by a shorter beam width after a large aperture area two single lenses, namely a negative meniscus and a planoconvex lens, which are inserted into Direction of incidence of light seen as the last lens completes the system, these two single lenses turn their curves towards each other.

Optical systems with a structure corresponding to this lens arrangement are ate high-quality, good corrected telephoto lenses known.

To correct the color of a lens, crown glasses with low dispersion, which is characterized by a high r-value, are generally used. combined with flint glasses of a larger dispersion characterized by a lower> value. On average, crown glasses have lower refractive indices than flint glasses. But there are also heavy and heavy crowns (SK and SSK) with higher refractive indices. With the help of these higher refractive crown glasses, many imaging errors, especially the field curvature, but also spherical and chromatic aberrations and astigmatism, can be corrected significantly more cheaply, thus increasing the performance results of the lenses.

Heavy and heavy crowns consistently have a glass price that is twice as high as that of the majority of all other types of optical glass. In the case of normal and wide-angle lenses in 35mm photography, the price of the glass is of secondary importance, since the diameter and thickness of the lenses and thus the quantities of glass are relatively small. With a telephoto lens with a focal length four times as large as a normal lens, which is 4 to 5 times the format diagonal, and with an aperture ratio of I: 2.8, which is relatively high for a long focal length lens, there are inevitably considerable lens dimensions in terms of diameter and thickness. Such lenses bring with them high glass prices, which have a correspondingly unfavorable effect on the final price of the finished product.

The purpose of the invention is to create a long focal length, bright telephoto lens of the known and powerful system type mentioned in the description at the lowest possible cost, without a reduction in the image quality occurring.

The invention is therefore based on the object of providing a well-corrected for small-house photography Telephoto lens with a focal length of 200 mm and a relative aperture of 1: 2.8 to be calculated at which avoids the use of heavy and heavy crowns and only inexpensive types of glass are used.

The invention solves the problem in that only types of glass are used in such a system come whose refractive index is on the one hand less than 1.64 with an i-value that does not exceed 50.

on the other hand is greater than 1.64, where the i-value is 35 does not exceed.

Research has shown that. In order not to impair the performance of the system, the high refractive indices of the positive components on the side of the longer radiation width cannot be dispensed with. However, glass combinations have been found which, instead of the SK and SSK glasses, use types of glass that have lower ι-values, yes'och equivalent refractive indices.

point. This is a barit shotgun [BaF]. whose i-value does not exceed 50.

If the refractive index of these types of glass is less than 1.64. the glass price is less than half the average value of SK and SS / C glasses.

The use of such BaF glasses with their low r-values compared to crown glasses can be carried out particularly well if heavy flint glasses (SF) are used as combination glass types whose i-value does not exceed 35, while the refractive index does not fall below 1.64 located. The demands made benefit from the fact that SF glasses belong to a very inexpensive group.

Lenses constructed in accordance with the inventive investigations with these glass combinations contain significant economic advantages because. as in the present case with lenses with a long focal length and a relatively high aperture ratio. the lens thicknesses and diameters have large dimensions and the glass price of the lenses alone is a multiple of their processing costs. The price of the end product can be reduced by using BaF glasses η π η instead of SK and SSK glasses. • be significantly si-.ikt.

A sectional drawing and a numerical example characterize an objective calculated according to the invention, the construction data of which are matched to a focal length of 100 mm, with an aperture ratio of 1: 2.8. Here L denotes the glass lenses, r the radii of the lens curvature surfaces. d is the axial center thickness of the glass lenses. / the air gaps between the vertices of the lire, η _ on the (/ -line of the helium spectrum (A = 587,> nm) related refractive indices of the optical glass types and ν the Abbe number decisive for color dispersion

60 len.

Example: / = 100; s' ^ 24.8 opening ratio 1: 2.8

r, ± * +56.5

di = 6.0 It ₁ a = 1.6056

J "2 - 00

/ ι - 0.7

43.9

'3 = + 27.5 »4 = - 250.0 r _s = + 20.0 »Ν, = -38.0 Γ7 = -63.5 r * = + 55.0

I. 1 797 285 , 6073 di = 14.0 (I ₂ = 1 , 7552 d ₃ = 3.7 (I ₃ = 1 I ₁ = 39.0 , 5697 d, = 1.5 H ₄ = 1 / 3 = 3.0 , 7283 ds = 1.8 »5 = 1 y (d + /) = 69.7

V ₁ = 49.2 v ₃ = 27.5

p ₄ = 49.5

'' 5

= 28.3

Claims (2)

Patent claims: 1. Five-element, four-element telephoto lens, The focal length is greater than the distance of the front lens vertex on the objective side from the image plane and is between 4 and 5 times the picture format diagonal to be displayed, its opening ratio is at least 1: 2.8 and it is structured in such a way that two positive system parts make one designed as a cemented member, enclose with its curvature the negative meniscus facing the object, which has an axial center thickness of less than 0.15 /, with the one on the side of Longer radiation distance standing positive system part consists of a converging lens, and the on The system part located on the side of the shorter radiation range consists of two individual lenses, one «Fidelity lens and one facing the image plane Converging lens, put together and the overall effect of these two I.lasen remains positive, thereby characterized in that only types of glass are used in such a system come whose refractive index is on the one hand less than 1.64 with an i-value not exceeding 50, on the other hand is greater than 1.64, the i-value 35 not being exceeded. 2. Objective according to claim 1, characterized in that construction data related to a focal length of 100 mm correspond to the values listed in the numerical example insofar as the individual surface powers (I n / r) by an amount of up to ± 0.2 //, the center thickness (d) of the lenses and the air gaps (I) of the lens vertices each differ by an amount of up to ± 0.03 · / and the individual 1-values by ± 5.0 from the specified values. Example: / = 100; s' = 24.8 focal ratio 1: 2.8 r, - +56.5 rf, --- 6.0 H ₁ = 1.6056 r ₃ = +27.5 r ₄ = -250.0 r ₅ = +20.0 r _h = -38.0 r-, = -63.5 r ₈ = +55.0 r _q = r / ι = 0.7 d ₂ = 14.0 </ ₃ = 3.7 I ₂ = 39.0 </ ₄ = 1.5 / 3 = 3.0 J ₅ = 1.8 H ₂ = 1.6073 H ₃ = 1.7552 n> = 1.5697 / 1, = 1.7283 ; -, = 43.9 V ₁ = 49.2 »3 = 27.5 H = 49.5 = 28.3 Σ (ά + Z) = 69.7 1 sheet of drawings