WO2018014954A1

WO2018014954A1 - Modular anamorphic zoom

Info

Publication number: WO2018014954A1
Application number: PCT/EP2016/067329
Authority: WO
Inventors: Joël Rollin; Jean-Marie Bacchus; Damien BIGOU
Original assignee: Thales
Priority date: 2016-07-20
Filing date: 2016-07-20
Publication date: 2018-01-25

Abstract

The general field of the invention is that of anamorphic zooms. The system according to the invention is modular. It includes a variable-focal-length first optical device (10), the image at each focal length being invariant in the image plane and at least one anamorphosis-producing second optical device (20B) and a third optical device (20A), said second optical device and said third optical device each comprising means for mating with said variable-focal-length first optical device, the assembly formed by mating the first optical device and the second optical device forming an anamorphosis-producing first zoom, said first device being placed in front of said first zoom, the assembly formed by mating the first optical device and the third optical device forming a second zoom, said first device being placed in front of said second zoom.

Description

Modular anamorphic zoom

The field of the invention is that of optical zooms and more specifically zooms achieving anamorphosis of the object, that is to say that the focal length of the zoom is different in two perpendicular directions. These zooms are called anamorphic in the following description.

These zooms are used either with digital sensors or with silver films. These anamorphic zooms have several interests. They make it possible to adapt the format of the shooting to the format of the detector, to use all its surface in order not to lose in resolution and sensitivity. Thus, it is possible to make a 16/9 format image on a 4/3 format sensor or a Cinemascope aspect ratio 2.35 image on a 16/9 format sensor. The format change gives the anamorphosis report. Thus, in this last example, the ratio of anamorphosis is 1 .33.

It is also possible to make a cinemascope image on a 35 mm film directly in the projection format equal to 22 × 18.6 to gain resolution at the time of shooting, and avoid the operation called "inflation", expensive and degrading the quality, necessary when shooting in Super 35 format to stretch image vertically by a factor of 2 when creating copies for projection rooms.

Finally, the anamorphosis allows to obtain artistic effects. The anamorphic shooting gives a feeling of long focus on a wide shot and a sense of closeness of the shots in depth due to the difference of focus according to the directions. Compared to the revolution optics, the reduced depth of field of these anamorphic combinations and the associated Bokeh effect contribute to the particular aesthetic of the anamorphic shots, the Bokeh effect corresponding to the blur of the backgrounds that lie outside. depth of field.

However, an anamorphic zoom is a complex optical objective. In essence, the zoom necessarily involves mechanical moving lens or lens group systems to achieve the desired focal length variations. This is a first difficulty. Moreover, achieving an anamorphic optical objective is not simple. Historically, three lens-based lens configurations for anamorphic shooting have been proposed. These configurations depend on the position in the optical combination of the anamorphic elements, conventionally made of cylindrical or toric components which can be:

- in front position of the lens;

- in afocal situation in the center of the objective;

- in an adapter situation on the lens mount. There are also optical solutions based on optical fiber image conductors, also known by the term "tapers" such as those described in patent CA 2088004 entitled "System and method for using anamorphic fiber optic taper to extend the application of solid-state image sensors ».

In the frontal position, the cylindrical lenses are heavy and imposing. It is a configuration that can offer significant openings but has the following handicaps:

- an optical quality that is often mediocre at short distances. The anamorphic optics provides aberrations for diagonal fields or aperture radii relative to the main axes of the cylinders;

- a large parasitic light;

- the presence of coma aberration;

- a large footprint;

- a significant weight that can reach 5 to 7 kg;

- an excessive price.

For example, patent US4382368 entitled "Focal Lenght Extender" implements an anamorphic system separated into two parts:

- A front part with cylinders.

- An anamorphic rear part, in front of the film plane.

The two cylindrical modules frame a conventional fixed focus lens with symmetry of revolution. It is also possible to perform anamorphosis using a prism system, as proposed in GB795001 entitled "Improvements in or relating to anamorphosing Systems". Prism anamorphosers, generally operating in parallel beams, are well known in the prior art, whether of the Brewster or Amici type. They generally present lateral chromaticisms difficult to correct on important fields, distortion and curvature on the lines perpendicular to the direction of the anamorphosis. However, patent FR2726916 entitled "Anamorphic lens and infrared imaging device equipped with such an eyepiece" which describes a solution combining a prism making all the anamorphosis and a prism used at least deflection to compensate for the chromatic, curvatures and lines and thermal drifts. On the other hand, the vertical field of the described application, with a linear detector strip, remains weak.

The so-called "back" anamorphic configurations are described in the prior art. By way of example of embodiment, mention can be made of US2006 / 0050403 entitled "Anamorphic Imaging System".

There are also solutions in which the anamorphosis is produced inside the lens. As an exemplary embodiment, US2007 / 0081257 entitled "Optical System including anamorphic lens" /

Anamorphic zooms are relatively rare. They all include cylindrical lenses located only in the front part, used to focus upstream of the drive. This one is composed of two mobile groups ensuring the variation of focal length and the conservation of the sharpness of the image. This configuration imposes cylindrical lenses of large dimensions, heavy, expensive and delicate to achieve because their specifications of shape and alignment in mechanics are strained. The presence of cylindrical lenses in the focusing element creates variations of the anamorphic coefficient with the focus, that is to say with the distance of the object whose image is to be formed. .

There are also optical complements or "attach" to interpose between a spherical zoom and the camera to stretch the image vertically, to cover the entire projection taking format. This makes it possible to take anamorphic shots with a standard objective and at low cost, but the optical quality obtained is poor because of the optical and mechanical constraints inherent to this type of solution,

Of course, in view of the foregoing, achieving an "anamorphic zoom" with a variable anamorphosis ratio is not possible. Currently, to change the anamorphic zoom ratio, the only solution is to change anamorphic zoom, which is a very expensive solution.

The anamorphic zoom according to the invention does not have these disadvantages. It includes two modular sets. The first provides the zoom function and the second the anamorphosis function. Thus, by changing only the rear part, we obtain a new anamorphosis ratio. More specifically, the subject of the invention is a zoom-type modular optical system, characterized in that said modular optical system comprises a first optical device with adjustable focal length, each focal length giving an invariant image position in the focusing plane and in at least one second anamorphic optical device and a third optical device, said second optical device and said third optical device each comprising means for coupling with said first optical device with variable focal length, the assembly formed by coupling the first optical device and the second optical device forming a first anamorphic zoom, said first device being placed in front of said first zoom, the assembly formed by the coupling of the first optical device and the third optical device forming a second zoom, said first device being placed in front of said second zoom.

Advantageously, the third optical device is also an anamorphic anamorphosis device different from that of the second optical device, the assembly formed by the coupling of the first optical device and the third optical device forming a second anamorphic zoom.

Advantageously, the third optical device is a revolution device, the assembly formed by the coupling of the first device optical and third optical device forming a third zoom without anamorphosis.

Advantageously, the second anamorphic optical device comprises cylindrical or spherical-cylindrical lenses.

Advantageously, the second optical device comprises, in this order, a plurality of spherical or spherical-cylindrical lenses followed by a group comprising said cylindrical or sphero-cylindrical lenses, said cylindrical or spherical-cylindrical lenses being closer to the exit of the second anamorphic optical device.

Advantageously, the second optical device comprises, in this order, a first group of cylindrical or sphero-cylindrical lenses, a plurality of spherical lenses followed by a second group of cylindrical or spherical-cylindrical lenses.

Advantageously, the second anamorphic optical device comprises an anamorphic prism device.

Advantageously, the second anamorphic optical device comprises, in this order,

a first group of spherical lenses arranged so that the entire system formed by the first optical device and said first group of spherical lenses is approximately afocal;

the prisms of the anamorphic device;

a second group of spherical focusing lenses.

The invention will be better understood and other advantages will become apparent on reading the description which follows given by way of non-limiting example and by virtue of the appended figures among which:

Figure 1 shows a half-sectional view of a zoom according to the prior art;

FIG. 2 represents a modular optical system according to the invention;

FIG. 3 represents a first optical combination of an anamorphic zoom according to the invention comprising a first anamorphic module; FIG. 4 represents a second optical combination of an anamorphic zoom according to the invention comprising a second anamorphic module;

FIG. 5 represents a third optical combination of an anamorphic zoom according to the invention comprising a third anamorphic module;

FIG. 6 represents a fourth optical combination of anamorphic zoom according to the invention comprising a fourth anamorphic module.

Figure 1 shows a half-sectional view of a zoom according to the prior art. It comprises single lenses 1 and optical doublets 2. This zoom includes a front portion 10 and a rear portion 20. The front portion 10 has groups of movable lenses called dimmers to obtain the desired focal length variations. The rear part has only fixed lenses, possibly adjustable at the factory. The set of optics is housed in a single mechanism 30 which comprises the organs for ensuring the variations in magnification, the development and the adjustment of the opening of the iris 3.

In the device according to the invention, the rear portion 20A of the zoom can be detached from the front portion 10. As can be seen in FIG. 2, a modular system is obtained in which the rear part 20A can be replaced by another rear portion 20B having different optical characteristics. Necessarily, these parts 20A and 20B comprise identical mechanical coupling means with the front part 10. These coupling means do not pose any particular problems for the person skilled in the art, the change of rear part requiring the mechanical means and the usual methodologies of assembly and disassembly of optics.

The rear portion 20 may be a radially symmetrical lens. But, the modularity is particularly interesting when the rear part is an anamorphic optical device. Indeed, one can easily, by technical cele, change the anamorphosis ratio to adapt to the shooting. Anamorphic modular zoom is thus obtained. In the case of anamorphic optical zoom, several variants of the anamorphic optical device are possible.

In a first embodiment, the anamorphosis is performed by cylindrical lenses. In a first variant, the cylinders are located only towards the output of the zoom, close to the film plane or the sensor as in an optical complement. By integrating the cylindrical surfaces directly into the rear group, the optical quality can be improved compared to a removable complement, but is nevertheless quite limited if one does not introduce a cylindrical surface close to the pupil, iris 3 of the figure 1.

In a second variant embodiment, the cylinders are distributed throughout the rear group, including the optical surfaces close to the iris. The nominal optical quality can be very significantly improved over the previous solution, but against the realization of cylindrical surfaces close to the pupil is more difficult. In addition, their positioning sensitivity makes this construction more difficult mechanically. In both cases, a better correction of the geometric aberrations is obtained by associating cylinders oriented horizontally and vertically, contrary to the optical complements which leave one of the directions completely unchanged, and therefore comprise only all parallel cylinders.

Alternatively, it is also possible to make an anamorphic toric lens. In a second embodiment, the anamorphosis is achieved through prisms, and no longer cylinders. This avoids the delicate realization of cylindrical surfaces. By cons, these solutions are longer and cumbersome, and require several prisms to have an output image in the axis of shooting. The apex angles of the prisms, their tilts with respect to the optical axis and the sequence of materials of the prism train are optimized to reduce distortions and chromaticism.

We can of course associate prisms and cylinders. In particular prisms close to the iris for the ease of realization of flat surfaces with high tolerances, and cylinders to the output in a less critical area for their small size. Figures 3, 4, 5 and 6 show different anamorphic modules made according to one of the above principles that can be coupled with a first module 10 zoom type. This first module 10 is identical in the four figures 3, 4, 5 and 6. It also corresponds to the front module 10 of FIG.

Each figure has two representations according to a first vertical sectional plane corresponding to the diagram at the bottom of the figure and a second horizontal sectional plane corresponding to the diagram at the top of the figure. In these section planes, the optical components are represented in continuous bold lines, the optical axis in em-dot dashes and the mechanical limits of the first module 10 and the second module 20 in dashed lines. Cylindrical or sphero-cylindrical lenses and doublets are denoted LC indifferently. The prisms are marked PR. The focal plane or film plane is noted P.

The systems of FIGS. 3, 4 and 5 all comprise cylindrical or sphero-cylindrical lenses with crossed axes. The axes are contained in the section planes. The modular optical system of FIG. 3 comprises a module 20C in which the anamorphosis is carried out by a kit based on cylindrical lenses LC. This rear group 20C is disposed between the iris 3 and the film plane P. The axes of the cylinders of the cylindrical lenses are all parallel to one of the cutting planes.

FIG. 4 represents a modular optical system comprising an anamorphic kit 20D in which the cylindrical or spherical cylindrical lenses LC are close to the film plane P.

FIG. 5 represents a modular optical system comprising an anamorphic kit 20E in which the first cylindrical or sphero-cylindrical lenses LC are at the front of the module 20E, towards the iris 3.

FIG. 6 represents a modular optical system comprising an anamorphic kit 20F in which the anamorphosis is performed by a system of PR prisms and lenses.

Claims

A modular optical zoom-type system, characterized in that said modular optical system comprises a first optical device (10) with variable focal length, the axial position of the image corresponding to each focal length being invariant in the plane of focus (P) and at least one second anamorphic optical device (20B, 20C, 20D, 20E, 20F) and a third optical device (20A), said second optical device and said third optical device each comprising means for coupling with said first optical device to variable focal, the assembly formed by the coupling of the first optical device and the second optical device forming a first anamorphic zoom, said first device being placed in front of said first zoom, the assembly formed by the coupling of the first device optical and third optical device forming a second zoom, said first device being placed in front of said second zoom.

2. Modular optical system according to claim 1, characterized in that the third optical device (20A) is also an anamorphic anamorphic device different from that of the second optical device, the assembly formed by the coupling of the first device optical and third optical device forming a second anamorphic zoom.

3. Modular optical system according to claim 1, characterized in that the third optical device (20A) is a revolution device, the assembly formed by the coupling of the first optical device and the third optical device forming a third zoom.

Modular optical system according to one of the preceding claims, characterized in that the second anamorphic optical device (20B, 20C, 20D, 20E, 20F) comprises cylindrical or sphero-cylindrical lenses (LC).

5. Modular optical system according to claim 4, characterized in that the second optical device comprises, in this order, a plurality spherical lens followed by a group comprising said cylindrical or sphero-cylindrical lenses, said cylindrical or sphero-cylindrical lenses being closer to the output of the second anamorphic optical device.

Modular optical system according to claim 4, characterized in that the second optical device comprises, in this order, a first group of cylindrical or sphero-cylindrical lenses, a plurality of spherical lenses followed by a second group of cylindrical lenses or spherical-cylindrical.

7. Modular optical system according to one of claims 1 to 3, characterized in that the second anamorphosing optical device comprises an anamorphic prism device (PR).

Modular optical system according to claim 7, characterized in that the second anamorphic optical device comprises, in this order,

a first group of spherical lenses arranged so that the entire system formed by the first optical device and said first group of spherical lenses is substantially afocal;

the prisms of the anamorphic device;

a second group of spherical focusing lenses.