Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Objective type
Patent
1998-06-18
1999-11-30
Manuel, George
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Objective type
359214, A61B 310
Patent
active
059930020
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an imaging device for observation of an object in an object plane comprising an optical system establishing an observation beam and a lighting apparatus producing a lighting beam, the optical system comprising an observation diaphragm having a slit with a longitudinal extension, said observation diaphragm moving in an intermediate image plane of the observation beam, the lighting apparatus composing a lighting diaphragm having a slit with a longitudinal extension, said lighting diaphragm moving synchronously with said observation diaphragm and in an intermediate image plane of the lighting beam said slits of the observation diaphragm and of the lighting diaphragm producing slit images in said object plane, said slit images substantially coinciding in said object plane.
An apparatus of this type is known from U.S. Pat. No. 3,547,512. Only a small area of the object is lit and simultaneously observed through the slit-like diaphragms in the observation beam path and in the lighting beam path. In order to nevertheless be able to examine a larger part of the object, the lighting diaphragm and the observation diaphragm are moved synchronously, whereby a part of the object is scanned. If the object is observed using a detector which has a certain degree of inertia such as, for example, the human eye, and if the movement of the slit images of the diaphragms is rapid enough over the same part of the object repeatedly, the individual images then blend into a complete image of the scanned part of the object.
This process is intended in particular to improve the viewing of an object through a cloudy, that is to say opaque, medium, in that it reduces the production and the observation of scattered light and the glare resulting therefrom, and can therefore be used, for example, in indirect ophthalmoscopy for observing the retina of the eye. In this case, a true intermediate image of the retina is produced outside the eye by means of an ophthalmoscopy lens, wherein the lighting apparatus and the optical enlarging system are focused on the plane of this intermediate image.
Nevertheless, a satisfactory result still cannot be obtained using the measures previously described. In U.S. Pat. No. 3,547,512 additional diaphragms and mirrors are therefore used, which each mask half of the observation and lighting beams respectively so that the observation beam and the lighting beam travel separately from one another except in a small section in the object plane. Although the scattered light produced and observed is successfully further reduced in this way, nevertheless, because of the reduction in the apertures of the observation beam and of the lighting beam, the light intensity and the resolution obtainable are considerably reduced. Similar apparatuses with the same disadvantages are also known from U.S. Pat. No. 4,170,398 and EP-A2 197 781.
Another method for reducing glare is the dark-ground process, in which the lighting beam is not imaged in the lens when no object is present. Observable light results only from diffraction on the object, wherein, however, a faithful image is not produced, so this process is only used for representation of contours.
The object of the invention is to provide a novel optical enlarging or reducing device which improves the known apparatus and produces an image of the object even when observed through cloudy media, which is as well contrasted and free of glare as possible, such that the finest details become visible. The light intensity of the device and the resolution obtainable should also be as great as possible.
Very generally, using an optical imaging instrument, the beams of light emanating from an illuminated object are imaged through a lens as an intermediate image, and this is viewed, enlarged, through an eye piece. According to Abbe, the illumination light beams are diffracted (modulated) by the object, wherein diffractions of the zero order, first order and so forth occur and interfere. The beams of high light intensity of the zero order (not diffracted) interf
REFERENCES:
patent: 3547512 (1970-12-01), Baer
patent: 4170398 (1979-10-01), Koester
Scanning, vol. 12, XP000255795; Burns D.H. et al.: Scanning Slit Aperature Confocal Microscopy for Three-Dimensional Imaging.
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