DE1958244C - Lens with an additional optical system to extend the focal length for photographic purposes - Google Patents

Description

/ • j -450 di = '2.7 H ₁ = 1.59 ι-, = 61 r. X d ₂ = 3.0 H ₂ = 1.65 v ₂ = 34 '3 -40 d $ = 1.5 • ■ 4 -95 d *. = 1.4 H ₃ = 1.59 ι ₃ = 61 ; - _s + 59 ds = 4.8 '6 -22 de = 2.9 H ₄ = 1.59 1-4 = 61 '■ 7 -116

The invention relates to a lens for photographic recording purposes with an additional four-lens, three-part optical system, which is used to extend the focal length of the taking lens between this and the camera, especially for 35mm formats, can be attached, with the additional optical system consisting of an achromatic lens built up as a positive, cemented meniscus, one Biconcave lens and a downstream meniscus is composed.

This additional optical system has to be attached or installed between the photographic lens and the camera has the ability to double the focal length of the taking lens used.

It has been found that known optical systems offered on the market for this purpose do not show satisfactory performance with regard to major imaging errors, which is particularly annoying in the insufficient contrast performance of the combined to a telephoto lens optical system is expressed. The purpose of the invention is to remedy this deficiency as far as possible to fix by adding the additional optical system Γη to the photographic lens em Inexpensive telephoto lens with a short, compact design results.

"The invention is based on the object of a combined, To create a telephoto lens, which consists of a short focal length photographic lens, that in order to double the focal length additionally with a multi-link. visually negative effect System can be combined. Here it is desirable the sum of the aberrations of the additional optical system within tolerable limits

echo. , _, ·,

The invention solves the problem by means of the numerical example given in the table in such a way that such an additional optical system consists of at least four lenses, which are combined in three members, in which the first two lenses are cemented, especially for reasons of chromatic correction and their color dispersion values. ·, have a difference of more than 24, that the achromatic L ₁ , L ₁₁ built up as Meni '- \ us of positive refractive power, whose two outer radii turn their hollow side towards the photographic taking lens and whose rear radius r _{3 is} smaller than 10% of the front radius r is cemented with a plan radius r ₂ so that a biconcave lens L _{111 follows an air gap d 3} which is less than 10% of the overall length, "the front radius r _{4 of which is} at least 1.6 times the rear radius r ₅ , which, after a further air gap d _{s, is followed by} a negative meniscus L _n , the rear radius r _{7 of} which is based on the value is at least five times larger than the radius r _b facing the hollow side of the taking lens. The advantages resulting from the invention are an increase in the conta-U performance and a good chromatic correction is guaranteed with regard to the required j-value difference.

The values in the sectional drawing and the following numerical data, in which the radii of curvature, with d the center thicknesses and air gaps of the lenses L, relate, according to the present invention, to a four-lens, three-part, additional optical system for doubling the focal length of the respective 35mm lens used. The refractive indices π are related to the rf line of the helium spectrum (;. = 587.6 nm), while the associated color dispersion values are characterized by the Abbe number 1 ·.

Numerical example

</, = 2.7 H ₁ = 1.59 ι ·, = 61

d ₂ = 3.0 H ₂ = 1.65. ' ₂ = 34

d ₃ = 1.5

d _A = 1.4 H ₃ = 1.59 1.3 = 61

d _s = 4.8

d ₆ = 2.9; i ₄ = 1.59 v ₄ = 61

C ₁ -450

V ₂ X

^r i -40

r ₄ -95

fs +59

r "-22

r ₇ -Π6

1 sheet of drawings

Claims (1)

Claim: Lens for photographic recording purposes with an additional four-lens, three-part optical system, which z. B. to double the focal length of the taking lens between this and the camera, especially for 35mm formats. the additional optical system being composed of an achromatic lens constructed as a positive, cemented meniscus, a biconcave lens and a downstream negative meniscus, characterized by the data listed in the table below, where the color dispersion value v _{d of} the first lens (L ₁ ) of the achromatic lens is around is more than 24 larger than that of the following lens (L ₁ ,) cemented with a plan radius, the absolute amount of the rear radius () - ₃ ) is less than 10% that of the front radius (; ·,), the following air gap (i / ₃ ) is less than 10% of the total length and the value of the radius (r ₇ ) lying in front of the image plane is at least five times greater than the radius (/ ■ <,) of the negative meniscus ( L _1V ) is: