Optical: systems and elements – Compound lens system – With relay
Reexamination Certificate
2001-02-21
2002-12-03
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Compound lens system
With relay
Reexamination Certificate
active
06490085
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical lens systems and, more particularly, to relay lens systems especially suitable for use in medical endoscopes and other optical imaging devices.
2. Description of Related Art
Medical endoscopes are used to view internal body organs through small openings created in and through the body wall or skin or by way of existing openings or orifices. Such instruments typically include a long, thin, rigid or semi-rigid optical cylinder that is mounted on or to a viewing mechanism or imager. When the endoscope is inserted and positioned for use, an image of the object being viewed is formed by an objective lens at the inserted or distal end of the endoscope. The image passes through a series of relay lenses along the cylinder to a viewer comprising an eyepiece or viewing lens or a video camera or imager at the viewing or proximal end of the endoscope.
The relay lenses must be very narrow and are typically in the range of about 2.4 mm to 6.0 mm in diameter and approximately 20 mm to 50 mm long. Each relay lens is commonly formed of two or more elements, and a pair of relay lenses make up a set of such lenses. Most endoscopes require two or more sets of relay lens pairs for proper operation. The number of sets generally depends on the length and specific requirements of the particular endoscope and/or the application for which it is intended.
Optimization of endoscope performance involves the adjustment, in the design and implementation of the endoscope, of many factors including brightness, contrast, resolution and corrections for various aberrations. Of particular significance are compensations for minimizing the basic Seidel aberrations (spherical aberration, coma, astigmatism, field curvature, distortion and axial and transversal chromatic aberration) as well as secondary spectrum and higher order aberrations. Typically, meaningful correction of one or more of these factors results in a concomitant loss of performance in one or more of the remaining factors.
Brightness of the image that is transmitted through a relay lens system is related to the ratio of the focal length and the diameter of the lens through which the image is being focused, a ratio commonly denoted the f-number. The smaller the f-number, the brighter the image transmitted by the lens. It is preferable in an endoscopic relay lens system to have a system f-number that is as small as possible so that maximum brightness is transmitted from the objective lens to the eyepiece. The resulting image brightness is also impacted by both absorption of energy by the lens media and unwanted reflection losses at interfaces of the lens elements.
Optical systems for medical endoscopes using relay lenses have been known since as early as 1879. In about 1908 a physicist from Zeiss, Moritz Rohr, developed improved optical systems for endoscopes using two or more relay systems. The introduction of anti-reflection coatings for optical components after the end of the Second World War allowed for the use of 3 or more relay systems in an endoscope.
In about 1959, H. H. Hopkins received a patent for a symmetric rod lens system. This relay system technology, and derivatives thereof, became the state of the art for most optical endoscope systems during the 1980's and 1990's. Although the Hopkins rod lens relay system corrects axial aberrations, it does not correct field curvature and astigmatism. Optical systems with that relay system necessarily require corrective elements in the objective system with extreme curvatures which are needed to compensate for the accumulated aberrations of the device's multiple relay systems. The disadvantage of such systems is that for relay lenses with higher numerical apertures, the higher order aberrations of the objective system are unable to fully compensate for the higher order aberrations that are accumulated in the multiple relay systems of the device.
In the 1980's and 1990's efforts were made to develop relay systems for disposable endoscopes. See, for example, U.S. Pat. No. 4,946,267 to Hoogland, U.S. Pat. No. 4,784,118 to Fantone et al., and U.S. Pat. No. 5,188,092 to White. These relay systems use pressed aspheres formed of plastic material. Glass rods with plane surfaces may also be added to increase the numerical aperture. However, these relay lens systems do not attain the image quality achieved by systems using only glass lenses, and neither do they meet the performance expectations of surgeons. In addition, the costs per use tend to be higher, overall, than for endoscopes using non-disposable relay systems.
U.S. Pat. No. 5,059,009 to McKinley discloses an endoscope relay lens system containing a symmetric pair of rod lenses in which long flint glass rod lenses are cemented on opposite sides of a biconvex crown glass rod that is formed from a glass ball. This relay lens system, which forms an imaging system, corrects the off-axial aberrations better than relay lens systems based on the Hopkins patent, although the correction is not complete. Specifically, the meridional image curvature is overcorrected, so that the meridional and sagittal image curvatures bend with the same curvature on both sides of the Gaussian image plane but with different signs. As a result, astigmatism remains in this system. Furthermore, the meridional and sagittal image curvatures bend further away from one another as more relay systems are added. Thus, even if the Petzval sum is corrected using strong curvatures in the objective system, the over-corrected astigmatism of this relay system can only be compensated by an under-correction of astigmatism in the objective system. The consequence is a detrimental effect on correction of the coma.
The shortcomings of the McKinley lens system were partially addressed in U.S. Pat. No. 5,568,312 to Horton, in which the relay lens system comprises three axially aligned cylindrical lens pairs, with each lens pair having two substantially rod-like lenses. The system uses three different materials—namely glass, cement and a polymer—as well as air interfaces to provide improved correction of chromatic and geometric aberrations. The effective f-number of each relay lens element is minimized, as is the number of lens element interfaces, to provide a brighter image. Problems, however, nevertheless remain in this system.
Relay systems currently available need to have both the axial aberration and off-axial aberrations corrected. The objective systems necessary to transfer the viewed object image to the entrance of the relay system and the eyepiece needed to transform the intermediate image from the end of the relay system to the image plane of the endoscope are only able to minimize the aberrations of their associated subsystem, and do not compensate for image aberrations that are accumulated in the relay system as a whole.
In addition, relay lenses for stereo endoscopes require a much higher numerical aperture than do relay lenses for mono endoscopes. Each of the two entrance pupils of a stereo endoscope must be as large as the single entrance pupil of a mono endoscope. But increasing the brightness of current stereo relay lens systems results in an unsatisfactory image. Currently available endoscope relay systems, when used in stereo applications, do not perform as well as mono endoscopes with such relay systems. Surgeons are therefore left in a disadvantaged position as the superior images produced in mono systems lack the apparent depth that can only be achieved with a stereo system.
There is currently a widespread and unsatisfied demand for better mono and stereo endoscopes. Surgeons using these instruments require that the image produced be both clear and sufficiently large and bright, with high resolution and low distortion. It is also desirable for there to be an appreciable three-dimensional or depth perception aspect to the image which requires a stereo relay system rather than a mono system. Finally, resolution in currently available endoscopic optical relay system
Cohen & Pontani, Lieberman & Pavane
Fineman Lee
Richard Wolf GmbH
Spyrou Cassandra
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