Optical: systems and elements – Compound lens system – Microscope
Patent
1993-01-25
1995-09-19
Ben, Loha
Optical: systems and elements
Compound lens system
Microscope
359201, 359385, 359729, 359731, G02B 2100, G02B 2608
Patent
active
054521254
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a confocal imaging system for microscopy and, in particular, to such a system which utilises slit scanning.
PRIOR ART
The principle of confocal imaging was first described by Minsky (see U.S. Pat. No. 3,013,467). Moving-slit, confocal imaging systems have been described by Baer (U.S. Pat. No. 3,547,512 and Lichtman (see Lichtman, J. W., Sunderland, W. J., and Wilkinson, R. S. (1989) in The New Biologist 1, 75-82. Also, forms of confocal microscope have been described in which a slit or bar pattern of light is scanned across the specimen and an image of this pattern formed by reflection or emission from the specimen is caused to fall on a stationary slit-shaped aperture. This use of a stationary slit is a feature of the systems described by Koester (Koester, C. J. (1980) Appl. Optics 19, 1749-1757., Burns et al. (Burns, D. H., Hatangadi. R. B. and Spelman, F. A. (1990) Scanning, 12, 156-160) and of the design of Brakenhoff and Visscher (Brakenhoff, G. J. & Visscher, K. (1990) Trans. Roy. microsc. Soc. 1, 247-250). A reflecting autocollimating system with no primary aberrations was described by Offner (see A. Offner, Optical Engineering (1975), 14, 131).
BACKGROUND TO THE INVENTION
Confocal imaging systems have become established as an effective means of eliminating out-of-focus interference in optical microscopy. In these systems only a very small area in the object plane is illuminated at any given time. The illumination in the object plane may be in the form of a single point, an array of points, a single line or an array of lines. A mask with the same geometrical form as the illuminating pattern is incorporated in a plane conjugate with the object plane, so that only signals from the immediate vicinity of the illuminated regions are admitted through the mask into the viewing system. In this way, interfering signals emanating away from the illuminated regions are rejected. A complete image is built up by scanning the illuminating pattern in such a way as to cover the whole of the area of the object plane, whilst keeping the mask in register with the illumination.
There are advantages in using a slit or array of slits rather than a single point as the pattern of illumination. For example, a complete image can be formed more rapidly and the instantaneous intensity of illumination required at any single point in the specimen can be reduced. An increase in the rate of formation of images (framing rate) is of particular value, since it can be used with direct visual observation to create the impression of continuous imaging. If a slit is used, it is desirable to be able to vary the width of the slit in the mask relative to that of the illuminated slit-shaped area. In some prior art, such as that of Lichtman, this is impossible, since one and the same mask serves to define both the illumination and the area of detection. The closest prior art, in this respect, is that of Koester, of Burns et al. and of Brakenhoff and Visscher, where the system is so constructed that the detection mask is stationary, so that the mask is easy to adjust in a continuous fashion during the operation of the microscope system. Koester's system fails to employ the full aperture of the objective lens of the microscope and is therefore compromised in image quality. The system of Baer depends on chromatic dispersion for its operation and is therefore not suitable for the main field of application of con focal microscopes, which is the examination of fluorescence in specimens.
The closest prior art (ie that of Burns et al. and Visscher and Brakenhoff) requires lenses to relay the image within the apparatus. This presents considerable problems since the chromatic performance of lenses is poor outside the restricted range of wavelengths for which they are designed. Also, in order to make the instrument conveniently small, the relay lenses must have high numerical apertures, which makes them difficult to design and expensive to manufacture.
THE INVENTION
According to the present inven
REFERENCES:
patent: 3951546 (1976-04-01), Markle
patent: 4170398 (1979-10-01), Koester
patent: 5035476 (1991-07-01), Ellis et al.
patent: 5225923 (1993-07-01), Montagu
Burns et al, "Scanning slit aperture confocal/microscopy for three dimensional imaging", Scanning, vol.l 12, May-Jun. 1990, pp. 156-160.
Amos William B.
Fordham James M.
White John G.
Ben Loha
Medical Research Council
Phan James
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