DE2319420C3 - Lens arrangement for variable magnification - Google Patents

Description

The invention relates to a symmetrical, axially displaceable lens arrangement according to the preamble of the claim.

With a constant axial distance between the image plane and the object plane, as is the case, for example in the case of copiers which is! • 'all, it is desirable to to change the magnification factor of the lens used in order to keep the image format To be able to depict objects of different formats. This is done by a well-known varifocal lens achieved (DT-OS 2044 514). which changes the magnification from 0.7 to 1.4 and which has two outer and two inner lens groups, each opposite a central aperture are arranged symmetrically and of which the distance between each of the outer and the inner is axially variable. The known lens is a double Gaussian variant of the first kind. It has been found that the variable magnification range

ho of the known lens only to compensate small differences in format of the object to be depicted can be used, but not for the illustration of objects whose form is much smaller than the basic format. It has also been found that the known lens is relatively large and heavy and therefore also during installation For example, in a copier, its dimensions and weight have an unfavorable effect.

It is the object of the invention to create a varifocal lens according to the invention which, compared to the known Lens is lighter and allows a wider variable range of magnification.

This object is achieved by an objective according to Ansoruch 1, its variable from 0.25 to 4 The enlargement factor ensures that the image of the most varied of object formats is kept on a constant one Image format is enabled. The lens according to the invention is a wide-angle lens, which has correspondingly short focal lengths and small dimensions and that accordingly for example, when installing in a copier, also requires correspondingly small connection dimensions and hereby and due to its low own weight contributes significantly to the fact that such a Copier can be built smaller and lighter. The invention is based on the drawings for example explained in more detail.

F i g. 1 shows on the basis of a diagram the working principle of the lens arrangement according to the invention, where the relationship between the displacement of the movable lens groups and the displacement of the entire lens system is shown for three different magnifications;

F i ü. 2 schematically shows the lens arrangement of lens according to the invention;

Fig. 3 is a diagram showing the change in the air gap between the movable lens group

HH '= S _n + 1 (HH \ + HH _n ) and the fixed lens group with regard to the change in the axial distance from the diaphragm to the plane of the object.

In the arrangement shown in FIG. 1, which dbnt to explain the working principle of the lens arrangement, the two movable lens groups 1, IV are farthest away from the diaphragm and are arranged symmetrically to it. The two stationary lens groups II and III are arranged within the movable lens groups, the axial distance between the main points of the adjacent stationary lens group and the movable lens group being S ₁ . The axial distance between the principal points of the two stationary lens groups is S _n . The total refractive power, hereinafter referred to as the power, of the movable lens group is </ ,. the total power of each stationary lens group is r / „. If one sets 7. + </ ,, = A (= constant) and _{(/ l7ll} = B {= constant), one obtains the equation for the total power of the entire lens arrangement:

Φ = tf (2 _Vl - BS _n ) B + A (I- AS _n ).

IS _x (ABS _n - A < _n - B)

(Il

If the principal point spacing of each movable lens group WW _{1 is} the principal point spacing of each stationary lens group HH ' _n , it is obtained. Principal point distance HH 'of the entire lens system as the following expression:

- S ₁ Bi] + [S _n + IStfJlA - e'.ß)] (A - S _t B) l'l> \ (2)

Equation 1 and equation 2 can be seen, 35 corresponds to the shift "" of the entire lens system. —P ^,. ■ _: ___ w .._: .. ui ™ ..- according to S, and C ₁ , to:

that Φ and HH 'are only functions of one variable t-. Therefore the equations can be written as Φ ^ \) and HH '(S _x ) . If the axial distance between the object plane and the image plane is R " , the following equation is obtained for the magnification [S of this optical system:

,,. = You ',) - S (c'j)

[HH'U ',) - HH'ie'jüß.

< ⁵ >

_ [R ₀ - HH- (S ₁ )]

- 2nd

(3)

- 2} ² - 4

From equation 3 it can be seen that the increase is also only a function of the variable t> \ . The equation can be written as ß (e \) . The axial distance S from the diaphragm of the lens arrangement to the plane of the object can be expressed as

S = [1 +

+ HH '(S _x ) Il (4)

S is also only a function of the variable S ₁ , so that S [Sf) can be used for it. It should be assumed that the movable lens groups are only moved between c \ and Sj . If for the total strengths of the entire lens system (?, · And Cj Φ (β \) and </>(t'jh the main point distances HH '[S ₁ ), HH' [Sj), for the magnifications [1 (Sj) , Ii (S :) and for the axial distances from the diaphragm of the lens system to the object plane S (S ₁ ) or S (Sj) is written, one obtains the From this equation it can be seen that the displacement of the entire lens system is also only 4s is a function of the variable S _x . Therefore, if one uses the axial distance S ₁ between the principal points of the stationary and movable lens groups as a parameter, the relationships between the total power of the entire lens system. 50 the principal point distance. the magnification, the lens group positions and the displacement of the entire lens system can be defined.

As mentioned, the lens system according to the invention has a pair of stationary lens groups, which are arranged in the vicinity of the diaphragm symmetrically to it are, as well as a pair of movable lens groups that are outside with a variable axial air gap in between are also arranged symmetrically to the aperture, so that the overall thickness of the whole M) lens system can be varied by changing the axial Distance between the fixed and movable lens groups is changed. This will make ti ie The magnification of the picture varies, while always doing the exact conditions for the picture being followed 6s because there is a subordinate relationship /. Wipe the amount of movement of the movable lens group and the amount of displacement of the entire lens system is made, although the axial

Distance / wipe the object plane and the Image plane over the entire magnification range is kept constant.

F i g. 1 shows at a, h and ν the relationship between the movement of the movable lens groups and the displacement of the entire lens system in connection with different magnifications. So for if the magnification is 1 /,;. at h the magnification 1 and at c the magnification '>', the object being labeled 1 and the images of the object being labeled 2.

The above statements relate to the case in which the entire lens system is divided into four lens groups is divided. Of these, a pair of stationary lens groups is arranged near the diaphragm, while the other two movable lens groups are provided outside of it. With a lens arrangement in which, in addition to lens groups 1, II. HI and IV, symmetrical to the diaphragm a pair of stationary lens groups is additionally provided outside the movable lens groups. is the mechanism for changing the magnification is essentially the same as that described above with the exception that Equations 1 and 2 slightly modified for the overall power and the main point interval of the entire lens system have to. This modification reduces the amount of movement of the movable lens groups, and there is an advantage in correcting aberrations.

In the claim, the construction data are Eitindungsgemcn lens arrangement stirred up. As shown in FIG. form four lens groups with twelve lens elements the entire lens system star.

where 1 and IV are the symmetrical movable lens groups and II and III are the symmetrical stationary lens groups. R denotes the radii of curvature of the successive refractive surfaces of the lenses, D denotes the axial thicknesses of the axial air gap of the successive lens elements. N denotes the refraction indices for the (/ line with a wavelength of 578 mn (Hg light) of the glasses of the successive lens clemenie.

ίο and I are the Abbc number of glasses of the successive lens clemenie. The indices assigned to the corresponding lens element are shown in FIG. 2 can be seen.
Typical time for the variable axial air gap /

Is and corresponding values for the equivalent P <distance / of the entire lens system, the main point interval HH ', the axial distance "S" from the diaphragm of the objective to the general plane and the magnification are listed below, with the axial distance R ₀ between the plane of the object and the image plane is 623.94.

/ 16,130 1 10,589 3,242 ./ 100.86 19.31 1 53.99 HH ' 13,170 456.5 10.453 7.9S2S S. 4S9.9 134.1 0.359 167.4 312.0 . ι 0.264 3.792 2.7S2 1.0

F i g. 3 shows the relationship between the variable axial air gap / wipe of the movable and dei stationary lens group and the axial distance .S from the diaphragm of the lens to the object of the standard lens.

For this purpose 2 blue drawings

Claims (1)

Claim: Symmetrical, axially displaceable lens arrangement for variable magnification with constant axial distance between the image plane and the object plane, consisting of two movable outer lens groups and two inner lens groups immovable with respect to the diaphragm, the distance between the outer and inner lens groups being variable, characterized in that the outer, movable lens groups (I, Ä, to R ₆ , IV, R ₁₉ to R ₂₄ ) have negative refractive power, while the inner lens groups (II, R ₇ to A ₁₂ , 111, R ₁₃ to R ₁₈ ) have positive refractive power, that six lenses are arranged symmetrically on both sides of the diaphragm and that the objective has the following construction data, where N is the refractive index for the d-line of the spectrum and V is the Abbe number: R ₁ = - «24 = 43.18161 O ₁ = D ₂₄ = 1.99514 A ₂ = - «23 = 70.30859 D ₂ = D ₂₃ = 5.4520! «3 = - «22 = -55.64474 D ₃ = D ₂₂ = 0.946 «4 = - «2, = 33.95923 O ₄ = D ₂₁ = 1.23186 «5 = - «20 = 36.53544 D ₅ = D ₂₀ = 3.45097 «" = D.
A ₁₉ = 167.11292 D, = D ₁₉ = variable «7 = - «18 = -538.71386 D ₁ = D ₁₈ = 2.46077 Rh = - «17 = -46.78787 D _s = D ₁₇ = 0.02358 R ₉ = - "." = -895.93699 D ₉ = D ₁ ,, = 0.72497 «10 - - «, 5 = 52.68860 O.o = D ₁₅ = 0.85464 «11 = -R ₁₄ ■ - = 60.71876 O _n = D ₁₄ = 1.71222 «12 = - «n = infinite O ₁₂ = D ₁ , = 1.89119 N ₁ = N ₁₂ = 1.62360 K ₁ = V ₁₂ = 46.9 N ₂ = N ₁₁ = 1.55957 V ₂ = - ■ C _n = 61.2 N ₃ = N ₁₀ = 1.53269 V ₃ = K ₁₁₁ = 45.9 N ₄ = N ₉ = 1.69346 V ₄ = I ₉ = 53.3 N ₅ = N _H = 1.66691 K ₅ = F ₈ = 33.0 N _h = N ₁ = 1.66986 V _h = V ₁ = 57.4