DE3907928C2 - Lens for large format cameras - Google Patents

Description

The invention relates to a large lens Angle of view for large format cameras with one front lens group consisting of several lenses and a rear lens group consisting of three lenses, between which an aperture is arranged.

Such lenses, which typically have an angle of view < than 70 °, for example 80 °, are among others rem as lenses for large format cameras puts. With regard to their use in the professional These lenses must range with respect to any image errors including chromatic image errors and esp especially the distortion should be corrected very well.

Known lenses with a wide angle of view usually have one on the lens group, which consists of three lenses. On An example of such a lens is that under the Name "Sironar" sold lens of the Optical Works G. Rodenstock.

Furthermore, a lens with a large angle of view, which, however, belongs to a different genre and in particular has eight lenses in six links, from the company Schneider sold under the name "Super-Symmar".

The two aforementioned lenses have in common that the Air space in which the aperture is arranged, comparative is small. This complicates the on, for example bring special screens, such as effect screens instead a usual aperture body.  

In addition, there is an eight-lens and six-element Objective relatively complex to manufacture.

The invention is based on the object of receiving a picture jective with a large angle of view, typically 80 ° should be to develop such that ver equally low construction effort and a wide rhin very good imaging performance a large free air distance between the front lens group and the rear en lens group, in which a possibly interchangeable Aperture body can be arranged, is present without that the overall length of the lens is essential changes.

An inventive solution to this problem is with their Developments characterized in the claims.

According to the invention, the front lens group consists of four Lenses. The focal length of the fourth lens in the front Lens group is approximately equal to or larger than the total focal length the total focal length of the lens. Furthermore, the radius the image-side area of the first lens is larger than that Radius of the object-side surface of the second lens front lens group.

By training the first and second Air lens enclosed in connection with the lens  additional lens in the front lens group The distance between the two lens groups is kept large the. In addition, this training allows a very small vertex distance between the first and the two th lens, so that the total thickness of the front lens group pe is relatively low. This changes the construction length of the lens hardly, since with the invention Objectively the contribution to the total focal length or to the refraction force between the two lens groups differently than with State of the art is distributed.

In particular, the training according to the invention "compact" structure of the ones arranged behind the panel Lens group possible without problems the one that was required for large format cameras, for example Observe focal length.

Furthermore applies to the air space d₂ between the first and second lenses of the front lens group:

d₂ <0.01 * f

where f is the total focal length of the lens. By this design of for the correction of the anterior lin This group of essential air lenses will be a special one partial refractive power distribution in the front lens group pe achieved, and at the same time the length of the front Lens group minimized.

The cementation also serves this purpose the second and third lens.  

According to claim 3 applies to the radius of curvature R₄ the putty area:

f <R₄ <2 * f

where f is the total focal length of the lens.

The invention is illustrated below with reference to embodiments play described with reference to the drawing ben, in which show:

Fig. 1 shows a lens section through an objective according to the invention, and

Fig. 2 is an illustration of the modulation transfer function contrast over the image field.

Fig. 1 shows a lens section through an inventive SLI lens. The individual areas are numbered 1 to 12 . The areas 1 to 7 form the front lens group, the areas 8 to 12 the rear lens group.

Mean accordingly

R _i the radius of curvature of the i-th surfaces (i = 1... 12),
d _i the axial distance between the vertices of the i-th and the (i + 1) -th surface,
n _{i is} the refractive index of the material between the i-th and the (i + 1) -th area, (n _i = 1 means air)
v _{i is} the Abbe's number of material between the i-th and (i + 1) -th area (not specified for air).

Furthermore, the beam path, to which reference is expressly made, is entered in FIG. 1 and the position of the diaphragm B1 is indicated.

Tables 1 to 5 give numerical data for five exemplary embodiments. The refractive index n _i and the Abbe number v _i are given for the d line.

The angle of view is in all design examples len 80 °, the f-number is approx. 5.6.

In all of the embodiments described below the following conditions are met:

d₂ <0.01 * f
n₁₀ - n₁₁ 0.05
v₁₁ - v₁₀ 15

Compliance with these conditions contributes in particular to Connection with both in the front and in the rear lens group existing putty surface for even Distribution of the correction loads in the individual Lens groups or those through the individual surfaces corrective aberration across all areas so that the lens is "relaxed". Furthermore, both in the front lens group as well as in the rear lens group pe all lens surfaces curved towards the aperture.  

Table 1

Table 2

Table 3

Table 4

Table 5

FIG. 2 shows the modulation transfer contrast function as a function of the picture angle for the exemplary embodiment given in table 5. Fig. 2 shows that the lens for a wide-angle lens for large format cameras with an angle of view of 80 ° is excellently corrected.

Claims (3)

1. Lens for large format cameras with an angle of view of at least 70 °, with a front lens group consisting of four lenses and a rear lens group consisting of three lenses, between which a diaphragm is arranged, with the following features:

• - The radius R₂ of the image-side surface ( 2 ) of the first lens is larger than the radius R₃ of the object-side surface ( 3 ) of the second lens of the front lens group
• - for the air space d₂ between the first and second lenses of the front lens group, d₂ <0.01 × fwith f: total focal length of the lens,
• - the second and third lenses are cemented together,
• the fourth lens has a focal length which is approximately equal to or greater than the total focal length f
• - in the front lens group, all lens surfaces are curved towards the diaphragm,
• - in the rear lens group, all lens surfaces are curved towards the diaphragm,
• - The second and the third lens of the rear lens group are cemented together.

2. Lens according to claim 1, characterized in that applies: n₁₀-n₁₁ 0.05
v₁₁-v₁₀ 13 where n _{i is} the refractive index and v _{i is} the Abbe's number of material between the i-th and (i + 1) -th area. 3. Lens according to claim 1 or 2, characterized in that for the Radius of curvature R₄ of the putty surface applies: f <R₄ <2 · f