Note: Descriptions are shown in the official language in which they were submitted.
206fi654
51 ~ AFOCAL OPTICAL IMAGING SYSTEM
The present invention relates to an afocal optical imaging system.
Such imaging systems are generally provided with an objective and an
l eyepiece and are known, for instance, as microscopes or telescopes, and particularly
10 telescopic sights. They are regularly used for purposes of magnification. In these systems,
particularly systems of greater magnification, it is difficult, as is known, to cover the desired
object field with the viewing field of the imaging system. The viewing field of an imaging
system, namely, regularly becomes smaller - for the same field stop - with an increase in
i magnification. In particular, its field of view is frequently considerably smaller than that of
15 the naked eye. Therefore, an object can frequently be easily sighted with the naked eye but
it will be difficult to find it again with a magnifying imaging system.
An afocal image-forming system is known, for instance, from German
DE-AS 11 76 893 (LOY). That publication discloses an afocal auxiliary-lens system for
magnifying the field of view of a telescope. Both the telescope and the auxiliary lens system
20 ~ always provide const~t magnification at all points.
From US 3 953 111 (FISHER et al), an imaging system with finite focal
length is known, i.e. a focal imaging system. This system consists of a group of several
lenses arranged one behind another. It portrays the regions of an object near the axis
substantially larger than regions which are remote from the axis. The nonlinear imaging or
25 magnification conditions produced thereby are compensated for by another imaging system
located optically downstream, i.e. imaged nonlinearly in the inverse direction. In the final
result, the object is imaged with the same magnification over the entire field of view. t
Regions close to the axis, to be sure, are of greater sharpness or, more precisely, have a
il better resolution of details.
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Furthermore, from German DE-AS 12 67 966 (SCHlELE), US 4 185 897
(FRIEDER) and US 3 708 221 (SCHAEFER), individual lenses are known which have
several coaxial zones of different focal length which extend transverse to the optical axis and
thus generally provide different degrees of magnification. A flat object which is at a
S constant distance from these lenses is therefore imaged on a surface the distance of which
from the lens is correlated with the changing lens focal lengths, i.e. it changes. The image
of the object thus generally does not lie in a plane but on a curved surface.
The present invention deals with the problem of eliminating, or at least
l reducing, the above difficulties when sighting an object by means of an afocal imaging
10l system.
! In accordance with the invention, this problem is solved in the manner that the
l angle magnification of the afocal system varies (Claim 1) transverse to the optical axis,
I ¦ preferably decreasing towards the periphery (Claim 2).
The advantage obtained thereby is essentially that the object is initially
15 ~ detected comparatively easily with the zone or zones of lesser magnification, whereupon the
optical imaging system is so positioned with respect to the object that the zone of greatest
magnification locks precisely on the object.
In accordance with the preferred embodiment of the invention (Claim 2), a
I zone of strongest magnification is therefore arranged in the vicinity of the optical axis and
20, 1 the magnification of the remaining zone or zones decreases towards the periphery. As a
I rule, the quality of an optical image decreases from the optical axis towards the periphery.
; The area of strongest magnification therefore lies in an imaging region which is particularly
favorable optically. A possible reduction in the imaging qualities of the zone or zones Iying
, I further from the optical axis can be tolerated. This region serves in any event essentially
25,, only for the initial, rapid detection of the object to be magnified and for the simple transfer
thereof into the central region close to the axis.
' I In accordance with another preferred embodiment of the invention, the
objective and the eyepiece are developed as follows in order to obtain zones of, in each case,
', predetermined, varying angular magnification of the entire system: In each case they have
30 zones which correspond to the zones of varying angular magnification and which also extend
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transverse to the optical axis and are mutually adapted in focal length to each other (Claim
3).
The zone having the strongest magnification is preferably developed as central
zone of constant magnification, arranged concentric to the optical axis, while the
S magnification of the other zones decreases stepwise and/or continuously towards the
periphery. In this way, symmetrical conditions exist for the optically important central zone,
so that favorable imaging conditions are created (Claim 4).
The symmetry of imaging is furthermore improved in the manner that all
zones are arranged with axial symmetry to the optical axis (Claim S).
Optimal symmetry is obtained in the manner that the central zone has a cross
I section in the form of a circular surface and is surrounded concentrically or coaxially by the
other zones (C]aim 6).
The initial fixating of the object to be magnified is facilitated to a particularly
, I great extent by a zone arranged in the peripheral region which is free of magnification or has
15, only a slightly but constantly magnifying or reducing effect (Claim 7).
The invention will be exp]ained below on basis of illustrative embodiments
with reference to the accompanying drawing, in which:
Fig. 1 shows an embodiment for magnification conditions which can be
I obtained with the imaging system, and
20 1 Fig. 2 shows a structural example.
In the drawings, parts having the same action generally bear the same
reference numerals.
!~ !
The embodiment shown in Fig. 1 has a circular central zone 30 of constant
I ! magnification (in this case, 4:1) arranged concentrically around the optical axis 20. The
25j central zone 30 is surrounded concentriically by an annu]ar transition zone 32 characterized
I l by a magnification which decreases radially outward from the optical axis 20. The transition
~' l zone 32 in its turn is surrounded concentrically by an annular peripheral zone 34 of constant
ll magnification. Its magnification, however, is less than that of the adjoining transition zone
! 32. In the embodiment shown, the peripheral zone 34 has a magnification of 1.1. Object
2 ~
and image are therefore of the same size~ The magnification can also be somewhat greater
or less (reduction).
The magnification conditions are indicated in Fig. 1 by black areas of differentsize. These areas are of the same size within the peripheral zone 34 and also within the
5 central zone 30, but much greater than in the peripheral zone 34. In the transition zone 32,
the areas become continuously larger from the outer edge towards the center, as is
additionally indicated by the starlike rays included in Fig. 1.
The dashed-line circles shown in Fig. 1 in the region of the transition zone 32
illustrate the possibility of a stepwise decrease in the magnification.
10~ Such magnification conditions not only afford the possibility of interesting and
suggestive optical phenomena, but also considerably facilitate the proper positioning of the
I afocal imaging system with respect to objects which are to be strongly magnified. The object
I ¦ can namely easily be initially found via the non-magnifying, or only slightly magnifying,
¦ ¦ peripheral zone 34. The central zone 30 is then already in approximately the proper position
15 ~' of magnification with respect to the object. There is then no difficulty in so aligning the
;I central zone 30 with the object that the object to be imaged is fully included by it. In this
case, the transition zone 32 permits easy optical transition from the peripheral zone 34 into
the central zone 30.
1 Fig. 2 diagrammatically shows one embodiment in the form of an afocal 20 I system, in this case an astronomical telescope.
Such a telescope, as is known, has an objective 10' - possibly composed of
! several lenses - and an eyepiece 10" - possibly composed of several lenses. The
I ¦ magnification of a telescope, or more precisely its angular magnification V, is described, as
I I is known, by the equation: V = f'/f", in which f' is the focal length of the objective 10' and
25~ 1 f" is the focal length of the eyepiece 10".
In the astronomical telescope, the distance d between the principal planes H'
, and H" of the objective 10' and the eyepiece 10" is the same everywhere, namely equal to
the sum of the focal lengths f', f", i.e. d = f' + f".
I The central zones 30' and 30" of the objective 10' and the eyepiece 10" are
30, arranged coaxially to each other on the optical a~iis 20 and together form the central
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magnification zone 30, which corresponds to the cent~al zone 30 of the embodiment shown in
Fig. 1. The distance apart d30 of the principal planes H30' and H30" of the central zones
30', 30" is equal to the sum of the focal lengths f30' and f30" of the central zones 30', 30"
on the objective side and the eyepiece side. In this connection, f30' is greater than f30n.
5 The central zones 30' and 30" on the objective side and the eyepiece side accordingly define
a magnification zone of constant angle magnification V, approximately 4:1, which is axially
symmetrical to the optical axis 20. The central magnification zone 30 has the shape of a
cylinder in the embodiment shown. In principle, it may also have the shape of a cylindrical
l cone.
10~ The central magnification zone 30 is surrounded concentrically by an annular
envelope zone 32 which is delimited at its free ends by a transition zone on the objective side
and on the eyepiece side 32', 32". The annular envelope zone 32 - unlike the transition zone
32 of Fig. 1 - is of constant magnification, for instance an angular magnification V = 2:1.
For the distance d32 between the principal planes H32', H32" of the transition zones 32',
151 32" on the object side and the eyepiece side, we again have d32 = f32' + f32N, f32' being
the focal length of the transition zone 32 on the objective side, and f32" being the focal
length of the transition zone 32" on the eyepiece side.
The annular envelope zone 32, in its turn, is concentrically surrounded by a
peripheral annular envelope zone 34. This annular envelope zone is delimited at its free ends
20; I by the annular peripheral zone 34' of the objective 10' and the annular peripheral zone 34"
of the eyepiece 10". The two peripheral zones 34', 34" have the sarne focal length f34',
f34". We therefore have f34' = f34". Accordingly, the peripheral annular envelope zone
34 has a magnification factor of 1, and therefore images the object in true size. For the
, distance d34 between the principal planes H34' and H34" of the peripheral zones 34', 34" on
25 I the objective side and the eyepiece side, we then have d34 = ~34' + f34", f34' being the
¦ focal length of the peripheral zone 34 on the objective side, and f34" being the focal length
of the peripheral zone 34" on the eyepiece side.
If one proceeds from the basis, as in the embodiment of Fig. 2, that the
Enncipal planes H30', H32' and H34' on Ih- ~ t s~de lie wi~hin ~he main plane H' of the
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objective lO' and that the same is true with respect to the eyepiece side, we then have the
following relationships:
d = d30 = d32 = d34, and
d = f30' +f30" = f32' + f32" = f34' + f34n.
In addition:
f30' > f32' > f34' for the objective lO', and
f30" < f32" < f34" for the eyepiece lO".
The different focal lengths can be obtained, for instance, by different radii ofl curvature of the lens zones, or as alternative or in addition also by different optical densities.
lOI The optical density and/or the curvature increases therefore stepwise on the objective side
from the optical axis towards the periphery. The situation is the reverse of this on the
eyepiece side.
! In principle, an annular lens can be associated with the two free ends of each
l annular envelope zone 32 and 34 and an entirety of optical axes 22 and 24 respectively can
lSI I be associated with each annular envelope zone. The entirety of optical axes 22 and 24
respectively covers a cylindrical envelope. The imaging system shown in Fig. 2 can
therefore be considered a system which is formed of a plurality of imaging units arranged
I coaxially to each other. In the embodiment shown, the annular lenses extend symmstrically
'I on both sides of the optical axes 22, 24. As an alternative, they can also be developed as
20, 1 "half-lenses" in such a way that they only lie on one side of the optical axes 22, 24 - on the
side, for instance, facing away from the central axis 20 on the objective side and vice versa
on the eyepiece side.
Furthermore, the focal lengths f32', f32" of the transition zones 32', 32" on
! the objective side and the eyepiece side can pass continuously from the focal lengths f34 and
25l~ f34" of the peripheral zones 34', 34" into the focal lengths f30' and f30" of the central zones
1! 30', 30". If no magnification takes place in the peripheral annular envelope zone 34, and
i therefore f34' = f34", these focal lengths can also extend into infinity. In other words, the
pedpheral annular lenses can be replaced by plano-parallel ~lasses.
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Finally, the central zone 30, the annular envelope zone 32, andlor the
peripheral zone 34 can be screened optically from each other, for instance by means of light-
impervious surfaces, layers and/or foils.
