The present invention relates generally to optical lens systems, and more particularly to lens systems suitable for endoscopes and the like.
In endoscopy and related fields, such as borescopes and dental scopes, the complete optical system is thought of as consisting of four basic and separate optical functions. Those functions are, in sequence of the direction of the travelling light, as follows:
This approach is the classical approach, and it is appropriate for the following reasons:
The disadvantage of treating the different optical components as separate entities is that the distribution of the optical powers is very uneven and that certain aberrations are naturally at a maximum, like astigmatism, field curvature, and chromatic aberrations. The correction of these aberrations require relatively short radii. These short radii are difficult to fabricate, require tight tolerances, and they are therefore the main contributors to the considerable cost of the fabrication of an endoscope. A truly inexpensive endoscope, sufficiently inexpensive to be offered as a disposable item, is presently not practical with conventional designs.
The present invention provides an integrated optical system suitable for endoscopes, borescopes, dental scopes, and the like which contains a minimum of elements and which elements have relatively long radii and need not be of a meniscus shape. The outside entrance pupil location is very suitable for a tapered probe or for concealment. The entrance pupil distance sufficient to accommodate a line-of-sight deviating prism is a natural consequence of the arrangement of the optical groups. The system leads itself to mass production and is highly insensitive to tilt and decentration of its components. As a consequence it is eminently suitable as a disposable item.
Broadly, the foregoing advantages are achieved in a lens system which is characterized by an integrated design which has an external entrance pupil and in which the majority of the groups are displaced from the image planes and pupil planes. In this way most components share in the pupil transfer as well as in the image transfer. Moreover, the aberration correction is distributed in an advantageous way over all the groups, providing relief to the first group which conventionally is in need of most of the aberration correction. It has been found that this integration of the optical functions and aberration correction is very beneficial in that it greatly simplifies the optical system.
A plano-convex lens, or even a double convex lens when used according to the invention can be corrected for astigmatism since it is displaced from the stop location. In this way no optical surfaces of very short radii are needed to correct the astigmatism of the total optical system. Furthermore, the spherical aberration of a convex-plano lens used in the present invention is very near the minimum possible for a single element. Also the chromatic aberration is greatly reduced by the displacement of the elements from the image planes and pupil planes as a comparison with the classical arrangement will readily show. A factor two to four in the reduction of the chromatic aberration is thus achieved without the presence of a chromatic aberration reducing element, sometimes making further color correction unnecessary. Even a system incorporating several transfers is fully color corrected by the use of a single color correcting element. The distortion, which is usually very high in the objective, is corrected at more convenient and effective places. The result is a single integrated system which replaces the three conventional separate parts, i.e. the objective, the field lens, and a relay lens. This single integrated system may be augmented, as is well known in the art of optical design, with additional optics, like a close-up lens, a field expander, a field flattening lens, or with additional relay groups, without falling outside the scope of the invention.
The illustrative embodiments to be described below are standardized to a length of about 100 millimeters of the basic optical system and mostly for a nominal magnification of unity. In this way the performance of the various examples can be conveniently compared. Embodiments with other magnifications, field of views, numerical apertures, and with additional relays are presented in order to show that the general concept of the invention is effective over a wide range of applications. The embodiments use conventional, non-GRIN (graded refractive index) lens elements, and thus each lens has a uniform refractive index. In
It is thus evident from these embodiments that the integration of the three groups of which a conventional endoscope exists, the objective, a field lens, and a relay lens, greatly reduces the overall power requirement. The reduction in the overall power requirement naturally reduces the amount of aberrations to be corrected which results in a considerable simplification of the optical system. An additional, and in many cases a very valuable, feature is that the optimal location of the entrance pupil is outside the system.
EFL = −5.518
.020 N.A.
60 DEG F.O.V.
MAGN = 1.000
EFL = −5.543
.020 N.A.
60 DEG F.O.V.
MAGN = 1.000
EFL = −3.216
.020 N.A.
60 DEG F.O.V.
MAGN = 1.000
EFL = −4.846
.020 N.A.
60 DEG F.O.V.
MAGN = 1.000
EFL = −5.495
.017 N.A.
70 DEG F.O.V.
MAGN = 1.000
EFL = −7.794
.025 N.A.
60 DEG F.O.V.
MAGN = .000
EFL = −5.301
.020 N.A.
70 DEG F.O.V.
MAGN = 1.000
EFL = −5.599
.020 N.A.
60 DEG F.O.V.
MAGN = 1.000
EFL = −4.891
.025 N.A.
60 DEG F.O.V.
MAGN = 2.000
EFL = 3.792
.025 N.A.
80 DEG F.O.V.
MAGN = −.500
EFL = −5.737
.017 N.A.
60 DEG F.O.V.
MAGN = .500
Column 1 Figure number.
Column 2 Numerical aperture at the output focal plane.
Column 3 Total field of view at the object side, in degrees.
Column 4 Magnification.
Column 5 Entrance pupil distance (air equivalent value), in mm.
Column 6 Number of elements with optical power.
Column 7 Number of image relays.
Column 8 Sum of the absolute values of all curvatures (i.e., the sum of the absolute values of the reciprocals of the radii of curvature), in units of 1/mm.
Column 9 Maximum image distortion in percent.
Column 10 Petzval sum of the total system, in units of 1/mm.
Colunm 11 Monochromatic peak to valley wavefront deformation over the whole field and unvignetted aperture.
Column 12 Axial chromatic aberration in waves.
This application is a continuation application of copending U.S. patent application Ser. No. 09/197,590, filed Nov. 23, 1998, now U.S. Pat. No. ______, which is a continuation application of U.S. patent application Ser. No. 08/687,910, filed Jul. 30, 1996, now U.S. Pat. No. 5,841,578, which is a continuation of U.S. patent application Ser. No. 08/351,481, filed Dec. 6, 1994, now U.S. Pat. No. 5,633,754, each of which is hereby incorporated herein by reference in their entirety.
Number | Date | Country | |
---|---|---|---|
Parent | 10397827 | Mar 2003 | US |
Child | 11226864 | Sep 2005 | US |
Parent | 09197590 | Nov 1998 | US |
Child | 10397827 | Mar 2003 | US |
Parent | 08687910 | Jul 1996 | US |
Child | 09197590 | Nov 1998 | US |
Parent | 08351481 | Dec 1994 | US |
Child | 08687910 | Jul 1996 | US |