WO2013131539A1

WO2013131539A1 - Object lens

Info

Publication number: WO2013131539A1
Application number: PCT/EP2012/003863
Authority: WO
Inventors: Witold Hackemer
Original assignee: Qioptiq Photonics Gmbh & Co. Kg
Priority date: 2012-03-08
Filing date: 2012-09-14
Publication date: 2013-09-12
Also published as: DE112012005996A5; DE112012005996B4

Abstract

The invention relates to an object lens (SA) with at least one fluid lens (VFL), which is preceded according to the invention by an afocal or quasi-afocal optical system. The afocal system preferably is or includes an optical Galileo system (AB) in retro position.

Description

lens

The invention relates to a lens with a liquid lens.

Liquid lenses, also referred to as liquid lenses or fluid lens or VFL, are well known. A liquid lens consists of two non-mixing ones

Liquids that have different refractive indices and electrical properties. By applying an electric field, the liquid lens changes its refractive index and thus its focal length, so that in this way optical functions such as focusing or focal length variation in the VFL application can be realized.

Such liquid lenses are known for example from WO 99/18456.

In 2002, a liquid lens of variable power (Fluid Lens) was known and made available (Varioptic, Lyon, France). This liquid lens variable

Focal length (VFL) has useful design parameters and useful imaging performance. Above all, this refers to the wavefront deformation and their

Stability with respect to the variable position of the lens in the gravitational field.

Information on the operation and parameters of a typical VFL (e.g., Varioptic Type Arctic A316): "Arctic 316 Technica data Sheet, Vers.l - December 2010".

The invention has for its object to provide a lens with a liquid lens whose imaging performance and sufficient focus over the known

Lenses with liquid lens is improved.

This object is achieved by the invention defined in claim 1.

Advantageous and expedient developments of the invention are specified in the dependent claims.

The invention will now be described with reference to an exemplary embodiment with reference to the accompanying drawings. All described, illustrated in the drawings and claimed in the claims features taken alone and in any technically meaningful combination with each other, the subject matter of the invention, regardless of their description or representation in the drawing and independently of their summary in the claims and their dependency.

It shows:

Fig.la - VFL application example No.l / ideal objective IO with liquid lens VFL, image from the infinite (beta '= 0)

Fig.lb - VFL application example No.l / ideal lens IO with liquid lens VFL, image of a near-object at the magnification beta '= - 0.10

Fig.lc - VFL application example No.l / construction data of the ideal lens IO with liquid lens in the positions for infinity and for beta '= -0.10

Fig.2 - VFL application example No.1 / field curvature and astigmatism at beta '= -0.1

Fig.3 - VFL application example No.1 / course of Strehlschen

Definition brightness in the field at beta '= -0.1

4 a - VFL application example No. 1 / MTF for the main color "e" for the axis point (y ¹ = 0) and for the maximum image height y '= 2.0 mm in the mapping from the infinite (beta ¹ = 0)

FIG. 4 b - VFL application example No. 1 / MTF for the main color "e" for the axis point (y '= 0) and for the maximum image height y' = 2.0 mm when imaging a nearby object at beta '= - 0.1

Fig.5 - VFL application example No.l / normalized color locus introduced by VFL at beta '= - 0.1

Fig.6 - a graphic on the theory of the afocal system Fig. 7a - a representation of a thin lens L of focal length f in the imaging from the infinite

Fig.7b - as in Fig.7a, but with an upstream afocal system AB with magnification ΜΑ _Π

Fig. 1c - as in Fig. Tb, but with a nearby object point F, shown at infinity

Figure 8 - VFL Application Example No.2 the layout of an embodiment of an inventive lens in the form of a stationary Anastigmaten

Fig.9 - VFL application example No.2 (embodiment) / the

Construction data of the objective according to FIG. 8 in the positions for infinity (beta '= 0) and for beta' = -0.1 1

10 a - VFL application example No.2 (exemplary embodiment) / MTF for the main color and four image heights y '[mm]: 0.0, 1.0, 1.5 and 2.0 when imaging from the infinite (beta ¹ = 0)

10b - VFL application example No.2 (exemplary embodiment) / MTF for the main color and four image heights y '[mm]: 0.0, 1.0, 1.5 and 2.0 when imaging a nearby object (beta' = -0.03)

10c - VFL application example No.2 (exemplary embodiment) / MTF for the main color and four image heights y '[mm]: 0.0, 1.0, 1.5 and 2.0 in the image of the near object (beta' = -0.06)

FIG. 1d - VFL application example No.2 (exemplary embodiment) / MTF for the main color and four image heights y '[mm]: 0.0, 1.0, 1.5 and 2.0 when imaging a nearby object (beta' = -0.11) The invention is based on the following considerations:

The variability in refractive power of a liquid lens described above, also referred to below as VFL, in the range of -13 Dpt to +35 Dpt, at first glance, presents a chance of simple variation of focal length and focusing distance in many optical devices. These typical functions could be performed without moving systems or system parts, ie lead to stationary systems.

The basic structure of a liquid lens is generally known to the person skilled in the art and will therefore not be explained in more detail here.

A theoretical analysis of the parameters of the VFL with regard to the applicability in optical instrument making, especially in systems with a significant

Information transfer factor, that is, those which must simultaneously have a larger finite value of aperture and field, presents the following difficulties:

A. the VFL introduces a variable Petzval sum into the system,

B. the VFL is a hyperchromatic lens of very low equivalent Abbe number (-14.3), it introduces a variable chromatic aberration into the system,

C. Very small free aperture D _VF L ⁼ 2.3mm for tunnel construction (VFL length = 2.0mm).

Consider the influence of the o.g. Difficulties regarding the construction of stationary objectives with anastigmatic field flattening with a total object field 2w> 40 ° and a f-number k <3.0.

The searched functions are:

1. Focusing for lenses of constant focal length

2. Focal length variation and focusing for zoom lenses (zoom).

Difficulty "A" apparently makes it difficult or difficult to achieve a planar image in the system for two lens power states of the VFL, a phenomenon that does not occur in the theory of classical variable focal length instruments. For this purpose, a first application example of a VFL is considered below.

VFL - Application Example No.l:

An ideal, aberration-free objective IO (component number i = 2) should be preceded by a VFL (i = 1) for adjustment to nearby objects. For this see Fig.la, b, c. The lens has a focal length f ₀ , a f-number k and an image circle diameter 2y '.

Known Gaussian relationships apply (system in the air: n = n '= 1):

k = 1 / 2sin (u '), where u' is the image-side opening angle

w = arctan (y Vfo), where w is the object-side field angle and y 'is the image height.

With the VFL a magnification β '= y' / y of at least -0.1 should be achieved.

Typical values for a lens adapted to a% "detector are, for example: focal length f ₀ = 3.14, f-number k = 2.8, image circle diameter 2y '= 4.0, field angle 2w

= 65 °

The large variation range of the positive refractive powers from 0 Dpt to +35 Dpt should be used, ie in the powerless state of the focusing lens, objects from the infinite are sharply imaged by the stationary system VFL + IO. Since there is a state of optical collimation between the objective and VFL, the focal length of the focusing lens necessary for achieving the magnification factor beta '= -0.1 can be defined as follows: fvFL = - £ _> / β'. This corresponds to the refractive power O _VF L ⁼ 000: fvFL and leads to a value of ~ 32 Dpt in the upper application case.

In this state, the VFL loads the system with a strong positive Petzval sum:

(1) This results in a Petzvalradius R _PeB = - 65.5. This radius describes the curvature of the image shell in its paraxial region, ie that natural image location which, in the case of corrected astigmatism and in conformity with the Petzval theorem, represents the location of a sharp image in the field. In the theory of aberrations of the third order (Seidel's space), such an image shell can be designed as a rotationally symmetric parabola. The defocusing path, ie the storage for a pixel with the ideal image height y ^* from an imaging plane, is: ds'p _ete = y ' ² / 2Rp _et2 (2)

For this see Fig.2.

For a planar detector (CCD, CMOS) with the image height y '= 2.00 is the

Defocusing ds'p _etz = - 3 Ιμπι. This corresponds to 3.7 times the wave optical

Depth of image, so ds' b'o.s ~ 3.7. The wave-optical image depth is the

Defocusing path of an ideal optical system in which the relative

Dot image intensity (DEH) drops to 80% of its maximum value. Its value depends only on wavelength λ and the system aperture A '= n' * sin (u ') and is defined:

For a diffraction-limited system in the air (n '= 1), the quotient ds' /b'o.8 <1 must be.

The real VFL additionally loads the system with the clamshell defect (astigmatism). This is the theory-compliant for the Aperturblendenlage in question, and the

Relationship between the meridional, the sagittal and the Petzvalschen

Bildfelalmimmung regulates for the Seidelraum the

Petzvalsche - sentence:

1

(4)

R'm, he The defocusing of the meridional and sagittal image shells is calculated accordingly: ds ' _mer = y' ² / 2R _me r

In the calculated example where due to the refocusing on β '= -0.1 the real defocusing at the edge of the field expressed in units of the wave-optical image depth has the following parameters: ds' _mer / b'o. ₈ ~ 17.9

ds' _sag / b'o.s ~ 7.3, Fig. 2 shows the course of the two shells and Fig. 3 the descent of the

Definition brightness DEH in function of image height y '[mm].

In the domain of contrast transmission (see Hopkins, H.H .: "The frequency response of a defocused optical system", Proc. Roy Soc., A231 (1955), Hopkins, H.H .: "The

Aberration Permissible in Optical Systems ", Proc. Phys Soc., B70 (1957), Jozwicki, R .:" Instrumental Optics ", publisher WNT, Warsaw 1970 (Polish)) requires the o.g.

Defocusing a sharp drop in MTF in function of the image height y '[mm] even for low spatial frequencies R [Lp / mm].

For the monochromatic evaluation at the main wavelength "e" = 546.074 nm, FIG. 4b shows the MTF progression in the spatial frequency continuum up to R = 200 lp / mm for the axis point (y '= 0, uppermost curve) and for the image height y' = 2.00 (T - meridional image location, S - sagittal image location).

FIG. 4a shows the monochromatic MTF for the case of powerlessness of the VFL (image from the infinite). The choice of the spatial frequencies shown depends, inter alia, on the pixel size of the electronic image imagers (CCD / CMOS) available today. Where R ^ _yq = 1 / 2P is the Nyquist frequency for a detector of pixel size P. Difficulty "B" apparently makes it impossible or difficult to achieve a stable correction of chromaticity error in the system for two VFL lens power states.

The condition for the Achromasie of the picture place is:

where:, the aperture beam height on the lens,

s' _p - the image-side system intercept

Δ ^ - the longitudinal color difference of the image location (eg, s _p = s ' _F. -S' _c .), V _; - Abbezahl the lens (eg v _e = -).

n _F. - n _c .

s ' _p = 0 is the prerequisite for the system after-radiation for two wavelengths (eg F'& o

It can be seen that this correction state is only influenced by the material characteristics of the lens material and the refractive power distribution of the lenses in the system.

A bipartite system VFL + IO, in whose terms the chromatic behavior with the powers Φ; and the equivalent Abbezahlen Vj is described in the approach as a doublet variant (p = 2) of thin lenses (interstitium = 0) are represented (VFL = 1, 10 = 2).

From (5a) can be written:

The refractive power Φ _{2 of} the objective is determined by the detector format (2y ') and the object-side field (2w). The maximum refractive power of the VFL depends directly on the defined Image scale (β ') in the image of nearby objects together. Since due to the collimation between VFL and 10, the aperture beam heights are the same (h ₂ = hi) and s' ₂ must remain constant (a system without adjustable components, stationary anastigmat), the compensation of the color misregistration in the system can be done by adjusting the equivalent Abbe number v ₂ in the real lens, however, can only be achieved for a refractive power Φι the focusing lens. For all other values of Φι, the VFL introduces a color error into the image. 5 shows the longitudinal chromatic aberration in units of the wave-optical

Depth of image b'o _. s (DOF) for three zone heights of the system entrance pupil.

Definition of equivalent Abbe number:

For each optical system composed of many optical components, each component (lens) of which consists of a defined medium having its own Abbe number, an equivalent Abbe number can be calculated.

Consider a wavelength triple:

F '= 479.9914 nm

e = 546.0740nm

C = 643.8469 nm

For each of these Fraunhofer lines we calculate the system focal length:

f (F), f (e), f (C)

For the boundary lines of the spectral interval we calculate the focal length difference: df = f (F ^* ) - f (C)

The relative focal length difference is equal to the negative inverse of the equivalent Abbe number V _{eq of} an optical system or optical assembly in the system: df / f (e) = -l V «,

Remarks. 1. The equivalent Abbe number V _eq states what value the regular Abbe number V (e) of a single lens with the focal length f (e) would have to have a chromatic property that is similar to that of the above optical system or group.

2. The regular Abbezahl an optical medium is:

V (e) = [n (e) - 1] / [n (F ') - n (C)]

This term describes the "dispersion power" of a glass; the difference n (F ') - n (C') is the main dispersion of the glass.

3. In chromatically corrected systems one speaks of the main wavelength (main color) and of an achromatic wavelength pair.

For system achromatization in the VIS area are:

- the line e is the main color

- The lines F and C form the achromatic wavelength pair

4. For the commercially available liquid lens (VFL) of the type Arctic A316 of Fa.

Varioptic (see above) is the equivalent Abbe number V _eq = 14.34; You value is in everyone

Lens position, or the same for each VFL lens focal length.

Another consequence of the refractive power variation of the hyperchromatic VFL lens in the system is the variable color magnification error:

Here mean:

Δν '- the lateral color difference of the image size y' _x -y _X2 , which can be generalized in the presence of chromaticity aberration to a Hauptstrahldurchstoßkoordinatenunterschied for two wavelengths AI, A2 in a defined image plane. y '- reference image height in main color, defined for example by A = VAl - A2

s \ · object section, related to the first lens ■ ίρτ _, ι - entrance pupil section, with respect to the first lens

A rj - principal ray height on the lens i

Other names see at (5a)

For a two-part system (p = 2) results:

For the finite position of the object and the entrance pupil, Δ / = 0 can be achieved when the parenthetical expression becomes zero. If both refractive powers are positive and constant, this can be achieved by opposing signs of the aperture beam heights and their corresponding ratio (corrective practice of some types of eyepieces) or opposite signs of major beam heights and their ratio (correction practice of many internal aperture diaphragm systems, e.g., photo-objectives). But if the first refractive power changes its value (VFL effect), then inevitably a color magnification error proportional to this refractive power change arises in the image.

The only way for a finite object position s \ to make the lateral color aberration Ay 'equal to zero and independent of the variations dc i is to strive for = 0.

This is equivalent to central passage of the main beam through the VFL, which must be ensured by the close proximity of the system aperture stop APE to the VFL.

This has far-reaching consequences for the astigmatic system load and its

Correction.

The difficulty "C" makes the construction of zoom lenses seem impossible or difficult.

Consider the case of a simplest zoom lens with the static elements and two liquid lenses that can form a variator and a compensator.

Even if one disregards the insufficient variability in the range of negative refractive powers, and even if a location of minimal lateral extension of all pharoid rays could be found for one of the liquid lenses, there is no second for the second VFL lens Place of comparable property available In compact systems the theoretical possibility for a conjugation of the pupil is omitted, see also US20110299176 AI.

The proof is provided by the extended invariant according to Helmholtz-Lagrange (Optical Invariant).

I = _{hpr> k} + -nnic iuic ₊ i - + hk + inic IWK + i = ypr, knkUk - h ^ Wk (7) h _k - height of the aperture ray on the surface of "k"

Uk - Aperture ray angle in the space after the area "k"

hpr.k - height of main ray at area "k"

w _k - principal ray angle in the space after the area "k"

The fluid lens available from Varioptic, referred to above, can be used only at the point of closest constriction of all the rays in the system where the pharoid waist Dphar is <2.3 mm. The Dphar ascents in front of and behind the waistline may only be moderate (tunnel effect), which means that a geometric limit value requirement is imposed on the

The principal ray angle VFL ^{m of} the direct lens environment and the meridional shortening of the ray bundle striving for the image corner is to be set in the VFL location.

The aberrations induced especially with larger VFL power increases cause a strong degradation in the performance of the system. At an ideal theoretical

Wide-angle lens with typical parameters for chip, such as k = 2.8 and 2w = 65 ° requires a first MTF zero point even at low spatial frequencies (R =.) To focus on near objects (beta '= -1/10) in front of the lens 0.3 - 0.5 * R yq) in the off-axis region (polychromatic, 420-680 nm).

This explains the lack of entry of these controllable elements into the device categories listed on the first page, as well as the failed general application of ^ on ^' opn ^' c lenses in lens construction in the mobile phone sector.

This raises the question of whether such liquid lenses still for the modern

Lens construction are attractive. For the miniaturized objective construction (stationary anastigmates for% "CMOS), the aberrations from the active VFL would have to be smaller by a factor of 3 ... 4. For the given lens, this is only for small refractive power variations, ie for very small ones

Focal length changes possible. The result is an absolutely insufficient stroke for the object setting, ie | ß '| = 0.033 ... 0.025.

This raises the question of how, with a small refractive power variation of the liquid lens, a large variation of the focal length of the focal length for the adjustment to nearby objects is sufficient for the magnification of at least β '= -0.1

Lens front group can be achieved.

Based on these fundamental and for the conception of lenses with liquid lenses fundamental considerations, the invention provides the following

Solution ready:

In instrument optics afocal systems and their theory are known. In the simplest case, an afocal system (in the light direction) consists of two lens groups A and B, wherein the image-side focus of the group A is coincident with the object-side focus of the group B. For this see Fig.6.

The particular transformation properties of the image by afocal systems describe three magnification definitions (systems in the air):

Angular magnification: M ⁼ tan (w ') / tan (w)

Transverse magnification: Mir ⁼ h '/ h

Longitudinal magnification: = ζ '/ z

M = M ² Tr If an afocal system with an angular magnification M _{AU is} placed in front of a lens L of focal length f, the effective focal length of the system thus formed becomes: £ β * = M * f.

7a shows a positive lens with focal length f and a beam path from left to right, where rays coming from an infinite object axis point are focused in focus F '.

Fig. 7b shows the same lens with an upstream afocal system AB. If the afocal system consists of a (in the light direction) group A of negative refractive power and a group B of positive refractive power, we speak of an afocal Galileo system in retroposition. The angular magnification of such an afocal system is positive (without image inversion) and 0 <M _A «<1.

In a system thus formed (AB + L), the rays in front of and behind the (AB) are collimated, thus the position of the focus F 'does not change. The effective focal length in the system, however, becomes shorter by the factor of angular enlargement ΜΑ _Π .

If the system (AB + L) is flipped 180 ° left-right or is the axial

Object point shifted from the infinite and positioned at such a distance left in front of the group A of the afocal system, that from the lens L to the right

extending beams to the optical axis and are parallel to each other

(ollimation state in the room behind L), that does not change anything

at the effective system focal length of (AB + L).

If L within the system (AB + L) changes its focal length from infinity (L powerless) to f, the effective focal length f _{eff of} the system (AB + L) changes from infinity to ΜΑ _Π * f. The objects are correspondingly imaged from infinity to the system front focus F sharp to infinity. See Fig.7c.

Thus, a means has been defined with a small power variation .DELTA..DELTA.Φ of the actuator L a strong, by the factor Μ _ΑΠ higher effective power _variation ΔΦ ^ to produce in the system. The afocal system AB can have a transverse magnification Μτ _Γ or a reciprocal of the angular magnification I ΜΑ _Π of 3 to 4. Thus, the maximum refractive power of the control lens can be reduced by a factor of 3 to 4, which corresponds to the sought size.

A small maximum refractive power of the Stellinse relieves the Petzval sum in the system according to formula (1), so that the field curvature and the resulting defocusing in the field according to formula (2).

This is a necessary basis for the promising compensation of the astigmatism introduced by VFL, whose fundamental behavior at low image heights or main ray angles is described by the formula (4) with the aim of anastigmatic field flattening. Both aspects together with the color-magnification-error-reducing measures according to formula (6b) enable a significant increase in the modulation at medium and high spatial frequencies and a homogeneous course of the MTF in the total field, ie an imaging property of the stationary anastigmatics adapted to the planar detector.

VFL - application example No.2:

The following definitions are to be assumed for the formation of a fixed, focusable objective (hereinafter called SA) with the parameters defined in Application Example No.1:

According to the invention, a liquid lens is preceded by an optical system which is or contains an optical galley system in retro-division. Under a motionless

(stationary) lens is understood according to the invention a lens in which a

Focusing and / or focal length variation without moving assemblies is realized.

The afocal galileo system AB in retroposition is called AFO.

Its angular magnification is MA _B -

The L lens of adjustable refractive power is referred to below as VFL (for example, the one commercially available under the name Arctic A316 from Varioptic

Liquid lens can be used). In the image space of the system (AFO + VFL) a basic objective HO is set.

The overall system of the stationary anastigmatism (SA) according to the embodiment is thus: (AFO + VFL + HO), see Fig.8.

By definition, a state of collimation prevails between VFL and HO

(Aberration-related deviations for aperture beams of +/- 10 ... 20 mR do not change the term "collimation"). Thus, the image-side focus F ' _H o = F'SA is the location of the detector (chip).

In the non-refractive state of the VFL, the object plane lies at infinity, at beta '= -0.1 1 the VFL has +7.55 Dpt, thus showing a factor of 4 smaller refractive power than in

Application Example No. 1.

The focal length of the basic objective is: fko ⁼ ISA ^ ΜΑ _Π

Because of the symmetrical central beam crossing through VFL (small color magnification error), the aperture stop APE in direct VFL proximity in the air space must be too HO.

In the equation ΜΑ _Π ⁼ tan (w ') / tan (w), with w and w ^* corresponding to the object-side and image-side

of the afocal system AFO.

For the principal ray angle in the space between AFO and VFL, VFL = w '= arctan [MAn * tan (w)].

For the principal ray angle in the space between VFL and HO: WVFL ⁼ HO ·

For a symmetric passage of all rays through the VFL center

^W VFL ~ W'VFL Low main beam slopes in the air spaces in front of and behind the VFL are welcome consequences of the AFO effect. This not only allows a low-loss energetic flow in the relatively long structure of the VFL, but also a favorable reduction of the lower Komastrahlwinkels in the image space and thus a low-loss coherent adaptation to the acceptance characteristics of the detectors (CMOS, microlenses).

Another consequence of the AFO effect is the dimensional increase in HO proportional to its focal length and the focal length S'F of the objective. In this way, the lenses are still useful and the aspects of immersion depth into the camera are taken into account (for such ultrashort focal lengths, the values s'p fs _A > 2..A must be reached for mechanical reasons).

Claims

claims

1 . Lens, with at least one liquid lens (VFL), which is preceded by an afocal or quasi-afocal optical system.

2. Lens according to claim 1, characterized in that the angular magnification of the afocal system is 0.2 <MA _D <0.7.

3. Lens according to claim 1 or 2, characterized in that the afocal system is an optical Galileisystem (AB) in retro position or contains.

4. Lens according to one of the preceding claims, characterized in that the lens (SA) is formed as Anastigmat or contains anastigmates.

5. Lens according to one of the preceding claims, characterized in that the lens is designed as a stationary (non-moving) lens, in particular as a stationary Anastigmat.

6. Lens according to one of the preceding claims, characterized in that the lens (SA) is a focusable lens and that at least one liquid lens (VFL) for focusing the lens (SA) is formed.

7. Lens according to one of the preceding claims, characterized in that the lens (SA) designed as a zoom lens) and at least one liquid lens (VFL) is designed and arranged to achieve a focal length variation.

8. Lens according to one of the preceding claims, characterized in that the liquid lens (VFL) has a free aperture Ό? _κ ,> 3.4mm, in particular of DF _re ~ 5.5mm.