Apparatus for measuring the refraction characteristics of ophthamological lenses

An apparatus for measuring the refraction characteristics of ophthalmological lenses comprises a projection optic for projecting light of a light source via a field aperture with a measuring figure and the ophthalmological lens arranged on a lens support onto a light reception means, the refraction characteristics of the ophthalmological lens being determined from the image site of the measuring figure in at least one direction. The apparatus for varying the vergency of the light beam on the object side of the ophthalmological lens between a position in which the refraction characteristics for the object distance are determined infinitely and at least one alterable position in which the refraction characteristics are determined for finite object distances. The lens support is the lens support means being arranged stationary and enables the ophthalmological lens to be definedly raised and positioned diagonally in the beam path, and at least one of a dioptric and prism compensation element is provided for disposition in the beam path of the diagonally arranged ophthalmological lens for enabling adjustment to a specific dioptric measuring range.

The present invention relates to an apparatus for measuring the refraction 
characteristics of ophthalmological lenses, in which a projection optic 
projects the light of a light source via a field aperture with a measuring 
figure and the ophthalmological lens, which is arranged on a lens support, 
onto a light reception device and the refraction characteristics are 
determined from the image site of the measuring figure in the lateral 
and/or longitudinal direction. 
Such apparatuses are also called apex refracting power gauges and are known 
in various designs, by way of illustration as automatic apex refracting 
power gauges, with which a test object is imaged, as projection or 
telescope apex refracting power gauges, etc. A not-all-encompassing survey 
of the different possible designs is given by the article "Gerate zur 
Messung des Scheitel-brechwertes" in Augenoptik, 1984, pp 67-70 and the 
article "Aufbau und Funktion von Me.beta.geraten zur automatischen Messung 
des Scheitelbrechwerts" in Deutsche Ootiker-Zeitung 3/1980 pp. 9-21. 
Prior art apex refracting power gauges usually operate with parallel beam 
paths and determine the so-called distance apex refracting power. A 
principle measurement error arises when measuring multi-focal lenses with 
apex refracting power gauges of this type. With regard to this, reference 
is made to Dr. W. Roos' articles, by way of illustration, in the 
Suddeutsche Optiker Zeitung, 1953, or his special print "Uber den 
Strahlengang im Nahteilvon Zweistarkenglasern". In order to eliminate this 
principle measurement error, an apex refracting power gauge has been 
suggested in which the lens can be rotated about an axial point located 25 
mm behind the eye-facing surface. This apex refracting power gauge is 
briefly mentioned in the article "Brillenglaser mit gleitender optischer 
Wirkung" by Dr. Josef Reiner, in the Suudd Ootikerzeitung, 1961, pp 114 ff 
and, in particular, on p. 116. Such apex refracting power gauges with a 
rotatable lens arrangement have not made a significant impact in practice. 
One reason for this is probably the complicated assembly plus the unaltered 
beam path, still yielding systematical measurement errors, which is 
intended for measuring the distance apex refracting power. 
The object of the present invention is to provide an apparatus for 
measuring the refraction characteristics of ophthalmological lenses, which 
also permits determining the so-called near apex refracting power, to put 
it more precisely, the effective use-value. 
A solution to this object, in accordance with the present invention, and 
further embodiments thereof is defined in the patent claims hereto. 
An inventive element is that the beam path of the apparatus can be altered 
corresponding to the desired distanCe from the object. When the "distance 
from the object is infinite", the beam path in most apparatuses is, 
however, not necessarily a parallel beam path. For measuring the near apex 
refractive power or the effective use-value, the vergency of the beam path 
is altered for the infinite distance from the object in such a manner that 
it corresponds to the use position. By way of illustration, in the case of 
a specific optical build-up of the invented apparatus, the parallel beam 
path may be converted into a divergent beam path (near vergency) by moving 
the projection optic and/or adding supplementary lenses. 
In order to hit the ophthalmological lens with this beam path, which 
corresponds to the use-position, the stationary lens support is designed 
in such a manner that the ophthalmological lens is positioned "diagonally 
to the beam path" in the beam path corresponding to the use-position. 
The divergence resulting from positioning the ophthalmological lens 
"diagonally" in the beam path in near apex measurement is compensated for 
by dioptric and/or prism compensation, by way of illustration, a lens or a 
small additional prism. 
By this means, without a rotation device, i.e. without moving parts, the 
effective use-value of ophthalmological lenses for near distances can be 
determined with an apparatus for measuring the refraction characteristics 
of ophthalmological lenses. 
It is particularly advantageous when the dioptric and/or prism compensation 
are integrated in the lens support. By this means not only the close 
spacial arrangement between the ophthalmological lens and the dioptric 
and/or prism compensation is guaranteed, but also the lens support and its 
respective compensation elements may be exchanged in one step. 
The invented embodiment of an apparatus may be combined with very different 
apex refracting power gauges. The apex refracting power gauges, may be, by 
way of illustration, projection apex refracting power gauges or even apex 
refracting power gauges, which measure the refraction characteristics 
automatically or, at least, display digitally. 
At any rate, it is advantageous if the sensors detect the vergency of the 
light beam and/or the beam path in the inserted lens support and/or the 
inserted compensation elements. By way of illustration, with an automatic 
apex refracting power gauge, the output signals of these sensors can be 
utilized to correct measurement results corresponding to the desired near 
distance. Also in the case of hand-operated apex refracting power gauges, 
in which only the display is automatic, the display can be switched to the 
near apex refracting power by means of the output signals of the sensors. 
At any rate, it is advantageous if the prism compensation, by way of 
illustration, is of variable design in that a Herschel compensator is 
provided.

A lens 1, having positive refracting power, and a lens 2, having negative 
refracting power, form together a collimator for the light of a light 
source 3, which is not shown in more detail. The vergency of the pencil of 
light behind lens 2 may, by way of illustration, be altered by moving lens 
1 in the direction of an arrow 11 and/or by exchanging lens 2 or by 
inserting an additional lens, which is not depicted. in the beam path. 
Not-depicted sensors, which, by way of illustration, detect the position 
of lens 1, inform the evaluation unit, which is also not illustrated, 
which vergency the beam path has during measuring. In the beam path behind 
lens 2 is arranged a lens holder or a lens support 4 for an 
ophthalmological lens 5, by way of illustration a bifocal lens. The light 
penetrating the ophthalmological lens 5 and the lens holder 4 is projected 
by an additional lens 6 onto a not-depicted light reception device. 
The lens support 4 is provided with a supporting surface 41 in such a 
manner that the ophthaLmological lens 5 can be placed on it with its near 
segment 51 in a specific angle of inclination to an optical axis 7. An 
exchangeable dioptric and/or prism compensation is integrated in lens 
support 4, which, by way of illustration, comprises a prism 42 and/or a 
lens 43, which can be put in the beam path selectively singly or combined. 
Moreover, the lens support is provided with recesses 44, into which the 
sensors, by way of illustration microswitches, engage. Depending on the 
position of the switch, an evaluation unit, which is not depicted in 
detail, is hit by signals, which inform the evaluation unit of the design 
of the lens support 4 situated in the beam path, that is the angle of 
inclination of the ophthalmclogical lens and the dioptric and/or prism 
correcton. 
The following table gives, by way of example, the support dimensions, the 
prismatic side effects and the prism for the preferred embodiments of 
invented lens supports for specific dioptric ranges of ophthalmological 
lenses 4 of the angles of inclination of ophthalmological lenses compared 
to horizontal lines. 
______________________________________ 
dpt- Support Angle of Prismat. Prism 
range size inclination 
side effects 
cm/m 
______________________________________ 
-7 2.1 16.degree. 
-10 0 
to to 
+8 +10 
+10 2,75 22.degree. 
+11 15 
to to 
+16 +20 
+16 2,9 23,5.degree. 
+20 20 
to to 
+20 +25 
-8 1,35 9,4.degree. 
-10 15 
to to 
-14 -20 
-14 0,8 6.degree. -17 20 
to to 
-16 -22 
______________________________________ 
In the preceeding section, the present invention has been described, by way 
of illustration, with reference to a preferred embodiment without the 
intention of limiting the scope or spirit of the present invention. Many 
very different modifications are, of course, possible within the overall 
inventive idea--to alter the vergency of the light beam and to arrange the 
lens defined diagonally to the optical axis and to additionally provide a 
dioptric and/or prism compensation. Thus many different measures may be 
carried out to alter the vergency of the beam path. 
Furthermore, by way of illustration, the lens support may be designed in 
such a manner that its angle of inclination is adjustable and it can be 
provided with many different correction elements.