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Патент USA US2068829

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Jan. 26, 1937.
|_. E, w. VAN ALBADA
Filed April 26, 19.32
3 Sheets-Sheet 1
Fig. 7.
Fig. 5
04.2444’; £~ 7714. ?x‘.
Jim. 26, 1937.‘ ‘
Filed April 26, 1932 ‘
'3 Sheets-Sheet 2
Jan. 26, 1937.
|__ E, w. VAN ALBADA
4 _
Filed April 26, 1932
- ‘
5 Sheets-Sheet 3
Patented Jan. 26, 1937
Lieuwe E. W. Van Albada, Amsterdam, Nether
‘ lands, assignor to the firm ofCarlZclss, Jena,
» Germany
‘Application April-26, 1932, Serial No.1 607,620
In Germany May 1, 1931
Application has been ?led in Germany
of the entire system is determined and, owing to
the collective,- ‘which lies in or near the common
4 ' The object of the invention is the construction
‘focal plane, having to image in conjunction with
' of reducing telescopic view ?nders which are free
the objective the‘ ocular lens as an entrance pupil
of distortion and have a very wide ?eld of view,
of the telescope at a suitable place‘ and, at the
same time; in conjunction with the ocular the
these ?nders being used in connexion with pho
tographic cameras and made of most simple op
objective approximately at the place of the‘turn
cost on a large scale. By simple'optical means
strument, also the power of the collective‘ is
determined, the consequence being that there
only remains to. give this collective the _‘ most
tical means which can be manufactured at low _ ing point of the eye of the person using the in
10 is to be understood piano and bi-convex lenses of
' plate glass or any other commonly used 'glass'. .
Either the telescopic view ?nders with simple -
thin lenses are not distortion-free, producing as
they do a strongly curved image ?eld which is due
15 to the arrangement of the lenses‘corresponding
in no way to the most favourable general effect,
or the absence of any distortion is obtained by
applying costly optical meansprohibiting large
scale manufacture.
The reducing telescopic view ?nder consists
in its simplest form of threev single lenses, viz.
‘the objective, the collective, and the ocular. With
favourable form and position possible. -
In the accompanying drawings, Figure 1 is a .
schematical reproduction of the theoretical prin-v
ciples. '
Figures 2 to 23 represent, each in a longitu
dinal section, constructional examples of the in
Figures 241an'd 25 illustrate details.
The condition of non-distortion ‘of a telescope '
of this kind may be described as follows:
Suppose that in Figure 1 017 represents the ob
a view to obtain the slightest distortion possible, .~ jective which images in its focal plane B a re- .
ticulated square (11 being disposed at an in?nitely
the distance apart of the vertices of the objec
tive and the collective facing each other» is made. , ‘ great distance, the ocular 0k having a focal
equal to at least 82% of the system represented:~ length which is twice as great will image also in
the common focal plane B (for instance a frosted ‘
by the focal length of the objective and the col
glass screen) and in approximately‘thesame size
With a view to obtain a ?eld of view‘ as wide > the reticulated square (12 which is half as big and
also ‘lies at an in?nitely great distance. - ' If both
30 as possible,‘ it is convenient to depart'from the images are identical, that is to say, if they have
bi-convex lenses usedso far and to apply as a,
front lens a piano-convex lens, and this because‘ the same distortion, the ?nder image will be free
plano-convex lenses produce an image field which of distortion. The image produced by the objec
is only slightly curved and distorted when the tive is more strongly distorted to the shape of a
barrel than that which is produced by the ocu-v 86
" 35 vplane surface ismade to face the object and
lar, which is'due to the ?rst image angle being‘
when the entrance pupil is at vthe correct dis
tance in front of the lens (this distance being twice the second one.- The consequence is that
‘approximately equal to the length of theradius) . there remains a difference .in the distortion, this
difference having to be corrected by the coIIec-I '
This favourable~ e?ect isv due to the nearly sym
This is possible indeed, since the collective
symmetrical path causing the slightest possible deviates the divergent marginal rays coming from
' ‘deviations. The image is distorted to the shape the objective towards the axis in a comparatively
offa barrel, since the deviation of the principal stronger convergent manner than the rays near
rays towards the axis is the stronger the farther I er thea'xis; The image produced by the objec
tive is thus given by theco'llective thehopposite
45 away these rays are from this axis when they distortion the value of which is to'be equal to the
traverse the lens, This distortion is to be neu
. above mentioned difference.
traliz'ed by thecollective and the ocular.
A telescopic view ?nder for vphotographic ' The distortion of a bi-convex lens is smallest,
> cameras conveniently produces a reduced image. that is to say practically equal to‘ zero, when this
of-the object,'slnce the ocular lens, which is
159 ‘small in itself and which is to beused also by
persons v.vvsaring spectacles, only can afford a
viewing angle inferior to that of the ?eld of view
I of the‘ photographic camerawhich embraces~ in.
.55 most cases more, than 50°.- ‘Inorde'rjto produce
lens istraversed by the principal rays as symq
metrically} as possible. If the collective is now
removed from the objective, the desired-correc
tion obtains-very soon because thedivergent prin
cipal rays traverse the collective in proximity to
the margin. Continuously increasing the dis
tance would cause"; super-correction and de
a de?nite diminution, for instance, ‘a two-fold
~ diminution, the focal length of the ocular is to be creasing the distance on under-correction. ' There
approximately twicethat of the objective since ' consequentlyexists a position iniwhich the collec
’ va common focal plane lies between both lenses.
tive exactly neutralizes theabove-mentioned dif
when theobjective is of a given size, the length ‘ference; this difference’ not being great,
2,068,829 a
the lens 0 could be indentical with the lenses a
favourable position is near that inwhich the prin
cipal rays have as symmetric a passage as possible. and b',- in which case,.however, the diminution
would be too slight to ‘furnish a clear image.
With, aviewto provide this correction in the objec
tive image, the ray pencils are to strike the col- " This ?nder is‘ characterized by a specially plane
lective previous vto producing an image. For
,this reason it would not be correct; to place the
image ?eld. -
‘The rear member of the objective-may be re-‘
placed by two plano-convex lenses whose vertices
collective behind the objective image, as has been
done sometimes, because in ‘this case it would
touch each other, because an approximately sym
leave the image on the object side unaltered and . metrical ray path is attained also in this case.
10 detriinentally in?uence the image which in Fig- , In Figure 4, the collective or second member 10
ure 1 is assumed to be on the ocular side, as well consists of two plane-convex lenses'b1 and b2. .
Telescopic view iindersaccording to the form
as greatly increase the curvature of the virtual
represented invFlgures 2 and 3, however, are not
image?eld. What requires being corrected is
readily adapted to be used in practice, since they
‘ the more strongly ‘distorted image on the object
15 side ‘and not the ‘slightly distorted image on the
ocular side;
furnish inverted images. For this reason the said 16
series of lenses require image reversion devices,
the manner'of the image reversion, which con
The lens ‘termed “collective” in the preceding
sists at least in a simple inversion of the ob
jects (that is to say, an inversion not neutralizing
the mirror effect), depending upon the type of 20
_ text therefore is in reality the rear member of an
objective consisting of two lensesw'hich in itself
20 furnishes a distortion-free image or, at option,
an image slightly distorted to barrel form. - Ow- . the photographic camera.
Figures 5 to 22 represent examples for simple
ing to the convergence of the leaving principal
rays, the latter image may be viewed by means Y image inversion and complete image reversion in
telescopes according to Figure 2 or 3, the simple
oia magni?er visually slightly distorting to cush
ion iorin, in which manner a ?nder image free of
distortion is obtained.
Slight alterations in shape of the lenses bear
only a slight in?uence upon the image, provided
that they do not in?uence too strongly the sym
metrical ray path.
The above is arithmetically explained in two
examples, namely, in Figure 2, in which the front
member a. is a plane-convex lens and in which
the collective or second member b is a loi~convex
lens, and in Figure 3, in which the collective or
second member b’ is planoeccnvex.
From the telescopic view ?nder according to
are obtained the following data:
inversion being attained by one re?exion on plane 25
mirrors or re?ecting prisms and the complete re
version by an even number of re?exions which
in most cases take place on roof prisms: -
In the example according to Figure 5 the ?rst
lens a, and in the example accordingto Figure 9 30
the ocular lens 0, may be ground .or cemented
to the roof of the re?ecting prism f.
The ocular lenses which touch with their ver
tices a plane prism surface may, when reversed,
be cemented to the said prism. ‘In this case 35
much of the ocular lenses is to be stopped down,
which is not practical.
In Figure 5 a roof prism j'in the ray path of
I the ?nder is disposed before the lens a, and in
Figure 9 behind the lens 0. In Figure 7 a re- 40
?eeting prism e lies between the lenses a and b, ‘
_ and in Figure-8 a plane mirror at is placed be- >
tween the lenses h and c.
As a rule, image view ?nders. are disposed lat
erally above the objective, which causes parallax 46
between ?nder image and objective image when
With an lens-es, ‘no is equal t0 recs.
The positionof the collective h, which ‘is ap
. proximately at equal distances from the ocular c
and the image 0’ ofv this ocular, shows that the
50 ray path through'the collective b is practically
symmetrical. This slight deviation from the
symmetrical ray path is just sufficient to com
pensate for the ‘distortion difference. The en
trance pupil E.p. is ata distance in front of the
front lens a which is equal to the radius; the im
age or the objective is behind the ocular c; the
' , the objective image, which‘embraces an angle of
photographs are to be taken at a short range.
This parallax can be avoided according to Fig
ure 6 by applying a telescopic view ?nder ac
cording to Figure 2° or 3 with vertical axis and 50
by disposing in front of the objective 9 of the
photographic camera a plano-parallel plate h in
clined atv45° towards the objective axis. The
telescopic view ?nder is so adjusted that the cen
tre oi the objective diaphragm ‘is the re?ected 55
image of the centre of the entrance pupil of the
?nder.' Below the plane-parallel plate is'pro
approximately 80°, lies near the rear side of the vided a deep-black layer.‘
In Figures 10 to 15 a prism body .eilecting a
lens 11, where the image vfield diaphragm B’ is to '
complete image reversion is disposed between the so
be positioned.
'- _
From-the telescopic view ?nder according to
Figure 3 are obtained the following data:
lenses 2: and c in the ray path of the linden The v
roof prism is in Figure 10 a straight-vision prism
T1, in Figure 11a so-called Porro secondaryre
version prism 3?, in Figure 12 an Abbe prism‘
i3, in Figure 13 a Leman rooi prism f‘, in which’ 65 '
the axial ray is displaced in parallel, in Figure 14
apentagonal Hensoldt prism f5 e?ecting an iden
tical parallel displacement and which has a root
with all lenses, no is equal to .1525. .rrne
practical advantage of the telescopic view ?nder
according to Figure 3, which comprises anaimage
held of 54”, consists in the two ?rst members
being identical ‘in themselves, which-simpli?es,
75 and reduces the cost of, the construction. Even
edge at one side and is at the contiguous‘ side con
nected to av totally re?ecting rectangular prism 70
e, and in Figure 15 two Dove prisms e'lylng be-.
hind each otherand whose re?ecting surfaces are
displaced relatively to each other at 90°._ ._
. In Figure 17 is illustrated (‘for the sake of dis
tinctness on somewhat too large a scale) a sys- 75
tem of four small roof prisms I" disposed before
the front lens a. Figure 17a illustrates the four
roof prisms f‘ as seen in the direction of the ar
rows in Figure 17. This system is a wide-angled
and completely reversing system which may be
very small.
In Figure 16 only a simple inversion takes place,
the. entrance pupil, as also in Figure 17, being
brought approximately into the centre of the re
versing system, which consists of two rectangular
prisms e2 whose’re?ecti'ng surfaces touch each
In Figure 18, two re?ecting prisms e3 are‘ placed
in front of the objective in such a manner that
15" their re?ecting surfaces act. inwardly. In Fig
ure 20,'the prisms e4 are placed in the same man
?nder image, owing'to the ?xed image ?eld dia
phragm, always corresponds vto‘the image pro
jected on the plate also when the image is only
simply inverted by means of a plane mirror.
If in a telescopic straight-vision finder the
image is-only simply inverted, the image ?eld
diaphragm must be either-stationary, according
to Figure 24, or revoluble through 90° about the
?nder axis, according to Figure 25, because the
?nder itself, or ‘at any rate its inverting system,
must be turned through 90° about the ?nder axis
when changing from a horizontally elongated to
a vertically elongated image.
When the image ?eld‘of the ?nder is hori
zontal, use must be made either of a stationary 15
cross-shaped diaphragm according to Figure 24
or of a diaphragm rotatable through 90° about
ford an image reversion for a very wide ?eld (up ‘ the ?nder-axis according to Figure 25, in which ,
to approximately 90") also when the respective case also the telescopic ?nder is to be rotatable
about an axis parallel to that of the photographic 20
20 pupil is just outside the system.
In Figure 19, the roof edges of four roof prisms objective. For this reason the arrangement ac
ner, but behind the ocular. Thesesystems af
f7 are turned towards outside in order to [effect
‘a complete image reversion over a wide ?eld and
within a narrow space. Figure 19a illustrates the
four roof prisms f’ as seen in the direction of
the arrows in Figure 19.
cording to Figures 8 and 9 with rotatable rear '
part is very suitable and advantageous.
I claim: .
1. A reducing telescopic view ?nder for photo 25
graphic cameras, comprising an Objective which
consists of two thin converging, lenses, a dia- '
respectively, are so placed between the lenses 1; -' phragm disposed behind the objective, and an
and c that the axis of exit is inclinedrelatively ocular, the distance apart of the vertices of those
In Figures 21 and 22 roofprisms f‘ and I’.
surfaces of the said two lenses _which face each 30
other being approximately 83% of the focal
D version may as well take place by means of a. length of the objective, and those principal rays
series. of lenses according to Figure 23, in which which traverse the said two lenses approximately
symmetrically providing‘ an image without dis
case all of the middle lens, except a small aper
35 ture, is stopped down. The objective consists of 'to'rtion and converging approximately at: the
the lenses 0 and b. The image produced by-the locus of the ocular.“
2. A reducing telescopic view finder for pho
objective is reversed by the lens i. The‘ ocular is
39 to the axis'of entrance.
Instead by re?exion, a complete image re
composed of the lenses 01 and c’. The data for
this lens series are as follows;
tographic cameras, comprising an objective which
consists of two converging lens systems, a dia
phragm disposed behind the objective, and an 510
ocular, the distance apart of the vertices of those
surfaces of the said two lens systems which face '
each other being approximately 83% of the focal
length of the objective, and those principal rays
which traverse the said two lenses approximately 45
symmetrically providing an image without dis
tortion and converging approximately at the
locus ofthe ocular.
3. A reducing telescopic view ?nder for photo
graphic cameras, comprising an objective which 50
consists of two thin converging lenses, a dia
phragm disposed behind the objective, an ocular,
and re?ecting means which de?ect the axis of
tically elongated pictures may be equipped with the-?nder, the distance apart of the vertices of
a fixed/rectangular image ?eld diaphragm, pro- . those surfaces of the said two lenses which face 55
Diaphragm behind lens To, 11:35
With all lenses, up is equal to 1.5.25.
Photographic cameras for horizontally and_ver
each other being approximately 83% of the focal
completely reversed image is
The same] length of the objective, and those principal rays
holds good in the case of Figures 8 and '9,'where, which traversethe said two lenses approximately“
however, the image ‘reversing re?ector _(or the symmetrically providingan image without dis-‘
prism) and the ocular lens are to be rotatable tortion and converging. approximately at the locus 60
vided that a telescopic straight-vision ?nder with
about the entrance axis of the ?nder. -_Independ=
ently of the position ofthis revoluble part,_the
' of the ocular.
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