DE1108935B - Optical system with variable focal length - Google Patents

Description

Variable focus optical system The invention relates to on optical systems whose focal length or magnification changes as a result is that at least two lenses or lens members along the optical axis at the same time be moved. These can be telecentric systems, i.e. telescopes act in which moving changes the magnification; meanwhile such telescopes can also be assembled with a photographic lens, so that the whole is a system of variable focal length. The Assembly also be carried out so far that to save optical means or to improve the correction on completely corrected telecentric ones The beam path between the telescope and the objective is dispensed with. The aperture and with it the pupil is in the downstream lens, better in front of it, around the To be able to keep the diameter of all lenses in the system small.

The system according to the invention belongs to the one proportionate little known type, in which one between two outer dispersing members collecting member is moved.

This type of construction has a major advantage over the more popular ones Systems in which a dispersive link is shifted between two collecting components will. In the latter case, the one with the longer focal length - in the case of the cinematographic one So recording the object - facing collection system have a focal length that the displacement of the negative link significantly exceeds. Because in the entire lens In principle, no real mapping can be created. That long focal length the front collecting link interferes with the close-up adjustment. It is known and absolutely necessary for focusing at close distances to move the front lens, so you in addition to the possibly for the Focal length change provided shift still a second adjustment option according to a distance scale or a range finder. As a result of relatively long focal length, the path of this shift becomes very long. It there is a risk of vignetting, all the more so because of the front components on the pupil lying far back and the scattering effect of the sliding following one Components must have a significant diameter, which is economical The aim is to keep reasons as short as possible.

These disadvantages do not apply to the subject matter of the invention, since for him the focal length of the front segment of negative refractive power, taken in absolute terms, is smaller is as the displacement path of the positive, arranged between the two spreading members Component.

This shortening of the focal length can also affect the others, in particular the displaced limbs are stretched and either leads to a proportionate short overall length of the whole system, compared to the ratio of the extreme enlargements; or you can set up the system with normal overall lengths so that the downstream Objectively a relatively short focal length, so for a given image or film format has an above-average angle of view. The lens according to the invention corresponds to this concept.

In addition, there are two possibilities in a known construction to be provided for the construction of the system according to the invention, since the collecting slidable member is made in two parts.

On the one hand, one can use the two negative ones that limit the displacement path Leave the links in place - apart from the shift for focusing and vary the distance between the two components of the sliding collecting member so that that the system, viewed as a telescope, remains strictly telecentric. Combined with a lens in a variable focal length system, it would Always design the resulting image in the same place. .

Such a system has the advantage that its outer length is constant is so that no slideways exposed for guiding movable components will. On the other hand, it is necessary for the movement of the two-part collection system to provide two curves, which, for example, as a helix in cut a guide cylinder, both do not have a constant slope, so are difficult to manufacture.

On the other hand, the collecting component can be moved as a rigid whole for which purpose a helical line of constant pitch is provided in a guide cylinder can be; then there is a second, generally containing a turning point Curve for the movement of the front member or that of the camera or the downstream Lens-facing link of the telescope required.

The optical system described here can be constructed in both ways and applied. With regard to the correction of color errors, it corresponds to this known experience that all individual components are achromatized have to. Otherwise there is a stable correction of the color error for all enlargements or focal lengths not possible.

The front component of the system according to the invention consists of three Lenses, an outwardly diffusing meniscus and a subsequent plano-concave or similarly shaped cemented link; this division is required to keep the high To accommodate refractive powers, according to the idea that the focal length, taken absolutely, smaller than the displacement of the following positive term is.

This consists of two achromatic systems, the distance between which is one type is constant and very small, while the other is variable.

The third fixed link of the lens system seen as a telescope is again an achromatic negative focal length.

When eliminating the geometric correction must be different from the usual Approach to be departed for each of the usual aberrations third order a surface or a component as particularly suitable for improvement is called. Rather, the subject matter of the present invention includes all imaging errors every single component to a minimum of their deteriorating effect has been brought. For this purpose, each lens element in the With regard to the pupil position and for each image point the position and cross-section of the light beam certainly; this was then evenly filled with arithmetically traced rays. The vast majority of this data for each component, i.e. in particular types of glass, Surface curvatures and thicknesses were then determined in a known manner so that the Totality of all rays for a pixel in the image space of the respective link passes through as small an area as possible. The size of this picture area was determined with a view to being repeated by the following optical links imaged, that is, enlarged or reduced in size, with the one designed on the film Final image a certain amount of blurring could not be exceeded under any circumstances.

The following table contains the optical data for a system that can be used as an attachment system for a taking lens for 8 mm film with f = 13 mm focal length, with the diaphragm between the attachment and the lens; the magnification of this telescope attachment varies between 0.53 and 2.26. The short focal length of 13 mm in this connection presupposes the relatively large angle of 25 'on the lens side for the telescope attachment according to the invention; nevertheless, the overall length is still considerably less than 90 mm. It is particularly advantageous that the effective focal length of 7 mm, which is very short for such a system, can be achieved. r1 -f- 123.9 dl = 2.5 1.639 / 55.5 r2 -f 41.2 h = 3.0 Y3 00 d2 = 3.0 1.805 / 25.5 r4 - 41.2 d3 = 2.5 1.643 / 47.8 r5 -I- 45.55 12 = 0.5 to 57.8 rs -i- 44.4 d4 = 6.0 1.658 / 50.8 r, - 66.9 d5 = 1.0 1.805 / 25.5 r3 -1-- 1007 13 = 0.1 (or 0.1 to 22.3 to 1.3) r9 + 39.1 d6 = 7.0 1.618 / 50.4 rlo - 39.1 d7 = 1.0 1.805 / 25.5 r11 - 123.9 (or - 132.0) 14 = 54.4 to 0.1 (or 57.5 to 0.2) r12 00 d 8 = 2.7 1.575 / 41.3 r13 - 12.25 (or 12.5) d9 = 2.8 (or 1.32) 1.620 / 60.3 r14 + 31.3 (or 32.5) Distance to aperture: 3.0 A longitudinal section through this lens system is shown in FIG. 1.

In Fig.2, depending on the telescope magnification V, are in logarithmic Scale the air gaps 12, 4 and their sum 12 -I- 14 plotted; this latter Curve is a picture for the required displacement of the negative front link, which contains the areas r1 to r5.

In the event that this front link when changing the magnification should not be moved, but that, as described, the two components of the collective link have a variable distance, the data in the table change only insignificant; the changes are indicated in the table in brackets. For this In this case, the air spaces 12, 13, 14, again depending on the magnification V, in Fig. 3 indicated. As can be seen, their sum is constant.

From these data it can be seen that the focal length of the three-lens Front link is f = -47.7 mm, i.e. smaller than the displacement of both positive components that are at least 54 mm. As a result of this short focal length the divergent element only needs about 3 mm to be moved to 1 m for close-up adjustment to become.

Claims (1)

PATENT CLAIM Optical system, in particular a telescope attachment, in which a positive component can be shifted between two negative elements in order to change the magnification, the focal length of the front system facing away from the downstream lens and, in absolute terms, smaller than that of the scattering front system that faces the object during the moving image recording Displacement of the positive two-part component, characterized by the following data, the thicknesses and distances with a tolerance of: E 5% of the total length, the surface powers with a tolerance of five times the reciprocal length, the refractive indices with a tolerance of: L 0 , 02 and the Ny values are to be understood with a tolerance of ± 3 units: r1 - + - 123.9 dl = 2.5 1.639 / 55.5 r2 + 41.2 11 = 3.0 r3 00 d2 = 3.0 1.805 / 25.5 r4 - 41.2 d3 = 2.5 1.643 / 47.8 r5 - + - 45.55 12 = 0.5 to 57.8 r6 + 44.4 d4 = 6.0 1.658 / 50.8 r, - 66.9 d, = 1.0 1.805 / 25.5 r $ -I-- 1007 13 = 0.1 (or 0.1 to 22.3 to 1.3) r9 - [- 39.1 d6 = 7.0 1.618 / 50.4 rlo - 39.1 d 7 = 1.0 1.805 / 25.5 r11 - 123.9 (or - 1 32.0) 14 = 54.4 to 0.1 (or 57.5 to 0.2) r12 00 de = 2.7 1.575 / 41.3 r13 - 12.25 (or 12.5) d9 = 2.8 (or 1.32) 1.620 / 60.3 r14 -1- 31.3 (or 32.5) Distance to aperture: 3.0 Documents considered: German Auslegeschrift No. 1032 571; . USA. Patent No. 2,165,341; British Patent No. 639,610; French patent specification No. 1 120 692.