Optics: measuring and testing – Lens or reflective image former testing – For optical transfer function
Patent
1998-02-12
2000-07-11
Pham, Hoa Q.
Optics: measuring and testing
Lens or reflective image former testing
For optical transfer function
356127, G01B 900
Patent
active
060880899
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an apparatus and a process for measuring the spherical, prismatic and cylindrical power of ophthalmic lenses having a measuring beam path directed at the ophthalmic lens lying on a lens support and having a device for the optical detection of representations engraved on certain areas of the surface of the ophthalmic lens. An apparatus of this type and a process of this type are known from DE 44 14 784 A1.
STATE OF THE ART
Devices for measuring the optical properties of ophthalmic lenses are also referred to vertex refractometers and are described by way of illustration in DE 40 03 144 A1.
Such known vertex refractometers are employed for follow-up control of already finished ophthalmic lenses in order to check whether the prescribed optical power has been achieved in processing the ophthalmic lens. Moreover, vertex refractometers are also used to check the correct centering of ophthalmic lenses inside the eyeglass frames, in particular, in lenses with a cylindrical and prismatic power in which the cylindrical axes as well as the prism reference point play a very important role in grinding the ophthalmic lens and for inserting the lens in the frames. Incorrect insertion of lenses of this type in the frames can lead to major impaired vision for the user.
Moreover, so-called progressive lenses, which are provided with lens areas for distant respectively near vision in addition to the aforementioned optical power and to the resulting symmetrical axes respectively optical reference points, are provided with two further geometric reference points which have to be taken into account in centering the lens in the frames.
By way of illustration, a progressive ophthalmic lens with a spherical, cylindrical and prismatic power provided with a distant as well as a near region can be determined by the following symmetry-defining axes and reference points (see the representation of FIG. 2a):
Fundamentally, an ophthalmic lens is divided by the horizontal line G of the lens into an upper and a lower region. In the center of the horizontal line G of the lens is a so-called prism reference point BTPT whose purpose is to facilitate control of prismatic power.
Above the prism reference point BTPT (BP) is the so-called centering cross Z which is simultaneously, on the one hand, the reference point for the positioning of the lens in front of the eye and, on the other hand, for the correct insertion of the lens in the frames. Usually, the centering cross Z is, by way of illustration, in Rodenstock lenses exactly 4 millimeters above the prism reference point BTPT (BP). Above the centering cross Z in the progressive lens shown in FIG. 2a, the distance reference point BTFT (BF) is disposed at a distance of 8 millimeters above the horizontal line of the lens. The corresponding near reference point BTNT (BN) usually is 14 millimeters below the horizontal line of the lens and is disposed approximately 2.5 millimeters nasally offset to the distance reference point in the center of the circle.
Manufactured ophthalmic lenses are provided with markings as shown in FIG. 2a in order to facilitate centering for grinding the lens to fit the frames. However, if the markings are no longer on the surface of the ophthalmic lens, two diamond-shaped markings R1, R2 which are unalterablely worked into the surface contour of the ophthalmic lens, define the position of the horizontal line of the lens. The markings are worked into the surface of the ophthalmic lens in such a manner that they are quasi invisible to the user. Ophthalmic lenses from Rodenstock are provided with other so-called micro-engravings, which permit reconstructing the type of lens and its respective reference values at any time, in addition to the unalterable markings R1 and R2 according to FIG. 2b. Furthermore, the addition A, which according to DIN 58203 represents the difference between the optical power of the near reference point BTNT and of the distance reference point BTFT, is provided as a number below the left diamond sho
REFERENCES:
patent: 3812374 (1974-05-01), Tuhro
patent: 4194814 (1980-03-01), Fischer et al.
patent: 5894348 (1999-04-01), Bacchi et al.
G. Rodenstock Instruments GmbH
Pham Hoa Q.
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