DE1497536C - Wide angle lens - Google Patents

Description

The invention relates to a wide-angle photographic lens with a large relative aperture and Back focal length.

The wide-angle lenses used in single-lens reflex cameras with folding mirrors have to be due to of the swivel space required for the folding mirror have a sufficiently large back focus, which in the generally larger than the focal length. The well-known wide-angle lenses have, with simple Construction but consistently a small opening ratio.

The object of the invention is therefore to provide a wide-angle camera lens with a large relative aperture and To create back focus that is accordingly suitable for a single-lens reflex camera, in particular the relative opening should be at least 1: 2 and the opening angle at least 60 °.

The inventive solution to this problem is characterized in the claim and described in the drawing; it shows

A b b. 1 shows an axial section through the objective according to the invention and

A b b. 2 the correction status of the lens.

The lens according to the invention is based on the following design considerations, which are known per se:

The wide-angle lenses, which have a larger focal length than the focal length, can be viewed by dividing the objective lenses into two groups of effects. Here, the 'front action group B _{1 has} a total of negative refractive power and the rear action group B _{2 has} a total of positive refractive power. The group B ₁ causes an extension of the back focus and an increase in the opening angle. However, there are the disadvantages that the coma correction is disturbed, in particular an internal coma easily arises, that astigmatism also occurs, in particular at an opening angle of more than 60 °, the sagittal image being more in the direction of overcorrection, ie in a more positive way Direction when the meridiorial image is curved and that a slight negative distortion eventually occurs.

The positive effect group B ₂ counteracts this tendency in whole or in part and above all corrects the final picture. In the present case it is provided in particular for B ₂ that this group is responsible for the correction of the coma and the correction of the astigmatism.

If these corrections are to be carried out by group B ₁ , it is necessary to increase the effective diameter of the lenses forming action group B ₁ , while at the same time obtaining a complicated structure in which a large number of lenses is required. This is not advantageous in terms of the weight and size of the lens.

From the point of view of the object, a positive individual lens L ₁ is therefore initially provided, followed by a negative meniscus lens L ₂ with a convex front surface. The action group B ₁ is made up of these two lenses. L ₁ is required to correct the distortion. The lenses L ₁ and L ₂ are followed by a cemented meniscus doublet with a convex front surface, the front lens L _{3 of which is} biconvex and the rear lens L _{4 of which is} biconcave. L ₃ has a higher refractive power than L ₄ . For their refractive indices "n ₆ and _7, the condition n _e applies greater than." ₇ At the same time, the cemented area r _{e is} negative and fulfills the condition

ίο χ> \ r _a \ > 0.5 / (/ = focal length). These measures support the correction of the coma of the light rays that fall outside the main ray at a predetermined angle. If r ₆ becomes positive, no effective coma correction is obtained. On the other hand, if the relationships are such that -r ₈ <0.5 /, then astigmatism occurs and the meridional image is negatively curved and difficult to correct. Behind the meniscus L ₃ , L ₄ is the diaphragm followed by a negative cemented meniscus doublet, the front lens L _{5 of which is} biconcave and the rear lens L _{8 of which is} biconvex. The refractive indices of L ₅ and L ₆ are denoted by H ₉ and H _10, respectively, and the radius of curvature of the cemented surface is r ₉ . If the conditions H ₉ > n ₁₀ , 3 /> r ₉ > 0.25 / are met, not only is it prevented that the light rays coming from within the main light rays show coma spots, the astigmatism is also corrected by bending back of the sagittal image curve against the positive direction in the negative direction. If r _{9 is} greater than 3 /, the cemented surface is ineffective in terms of coma correction, and if r _{9 is} less than 0.25 /, the sagittal image is excessively curved in the negative direction, which adversely affects not only the astigmatism but also the coma and the correction becomes difficult. The total focal length, viewed up to r ₁₀ , is negative. This is a remarkably effective factor in increasing the back focus. The next two downstream single lenses, a positive single meniscus L ₇ with a concave front surface and a biconvex lens L ₈ , have the function of being that of the lenses L ₁

. to L ₆ generated virtual image to convert into a real image that appears in excellent quality in the film plane. In addition, the lenses L ₇ and L ₈ are effective for correcting the spherical aberration. Therefore, according to the invention, it is possible to provide a high efficiency, small and light weight wide angle camera lens which has a large aperture ratio (at least F: 2), as well as one

opening angle above 60 ° and a long back focus, at the same time, the state of correction is excellent over the entire image area.

The objective according to the invention has the values specified in the claim, the values shown in FIG. 2 shown Correction status and the Seidel coefficients listed below:

I. U IIMV IV V 1
2
3
4th
5
6th
7th 0.007334
0.0071112
0.00779256
-4.1299708.
1.8270342
0.1799666
- 0.2755608 0.0179086
-0.0375082
0.0109298
0.9848172
0.3143200
-0.1575342
-0.2541436 0.0874548
0.3956748
0.0301458
- 0.4696714
0.1081502
0.2757958
-0.4687822 0.1733250
0.1978374
0.2603874
-0.9479318
0.5016076
0.1775524
-0.5941258 0.4232080
-1.0434910
0.3590868
0.2260402
0.0862958.
-0.1554210
-0.5479492

(Continuation of the table)

I. II III-IV IV V 8th -0.8667396 0.4853216 -0.5435012 -1.0055318 0.5630368 9 -0.2688630 -0.1238492 -0.1141000 -0.0690544 -0.0318092 10 0.6274540 -0.2536652 0.2051020 0.6975688 -0.2820110 11th 0.0010942 -0.0044824 0.0367250 -0.1236774 0.5066446 12th 1.2946352 -0.4351878 0.2925742 0.5522526 -0.1856380 13th -0.0006468 0.0097138 -0.2917586 -0.0277420 0.4166180 14th 2.0788050 -0.6138424 0.3625182 0.3755416 -0.1108922 Σ 0.4895778 -0.0572022 -0.0936720 0.1680096 0.2237184

For wide-angle camera lenses with a large aperture ratio, A number of problems exist for use in single lens reflex cameras, e.g. B. Size or shape of the lens, elimination of the coma or the like. There are a number of difficulties in the Lens construction exists and only a few suggestions have been made to date.

In the present invention, particular attention has been paid to the correction of coma, therefore sufficient peripheral light can be used, and it is possible according to the invention to produce a wide-angle camera lens having a large aperture ratio, whereby various lens defects can be corrected excellently, with the result that it is possible to obtain a back focus of 1.1337 / with an aperture ratio above F: 2 and a field angle above 60 °. It can also be at full

Focal length / - 1.0
Opening angle 2vv == 62 °
relative opening F : 2
Back focus B- f - 1.1337

Aperture an excellent contrast can be obtained. It is also possible to change the lens diameter of the foremost components to comparatively small values, around 1.3 /. Therefore There is also an advantage in that the diameter of possible additional lenses or filters is approximately remains limited to 1.5 /.

Claims (1)

Claim: Wide-angle lens with a large relative aperture and focal length, characterized by the following data for the radii of curvature of the individual lens surfaces n, the axial lens thicknesses or air gaps dt, the refractive indices m, and Abbe numbers, above all, all counted from the object side: Vd V ₁ = +3.2117 "1 = 0.10833 "1 = 1.0 53.9 r ₂ = oo J ₂ = 0.00278 H ₂ = 1.71300 r ₈ = +1.3889 ^ 3 = 0.06111 «3 = 1.0 64.2 r ₄ = +0.4778 J ₄ = 0.31111 «4 = 1.51680 r ₅ = +0.8945 <4 = 0.22778 «5 = 1.0 41.9 r ₆ = -1.5278 J ₆ = 0.29167 «6 = 1.66755 54.62 r ₇ = +0.9444 J ₇ = 0.14722 II ₇ = 1.51454 r ₈ = -0.5992 J ₃ = 0.02778 "8th = 1.0 26.1 r ₉ = +1.0775 J ₉ = 0.19444 «9 = 1.78470 49.4 Ίο = -0.7172 d ₁₀ = 0.00278 «10 = 1.74443 r _u = -3.0556 J ₁₁ = 0.08333 «11 = 1.0 46.2 r ₁₂ = -1.0691 d ₁₂ = 0.00278 «12 = 1.76684 r _u = +3.6111 slide = 0.06944 «13 = 1.0 44.9 r ₁₄ = -2.1958 «14 = 1.74400 «15 = 1.0 1 sheet of drawings