Optical: systems and elements – Single channel simultaneously to or from plural channels – By refraction at beam splitting or combining surface
Patent
1996-09-19
1998-03-31
Nelms, David C.
Optical: systems and elements
Single channel simultaneously to or from plural channels
By refraction at beam splitting or combining surface
359629, 359633, 359637, 3589091, 396111, 396452, 396707, 396730, 396913, 396866, G02B 2712, H04N 5225
Patent
active
057345074
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention is concerned with an optical beam splitter and particularly with an electronic high speed camera incorporating a beam splitter.
Reference may be made to DE-C-4212271, which discloses an electronic high speed camera incorporating a pyramid mirror as a beam splitter. Light from an object is imaged by means of a camera objective, via the facets of a pyramid mirror on to a number of electronic image sensors arranged around the pyramid mirror. The camera objective is common to all the image sensors. In order to perform high speed photography of a short duration event, the image sensors can be exposed one after the other by means of fast acting electronic shutters.
The arrangement disclosed in the above patent has a number of inherent disadvantages. It is difficult to ensure that each of the several images formed by means of the beam splitter is evenly illuminated over the extent of the image. Further, there is nothing in the above German specification showing how to adjust the focusing or the aperture of the camera objective, and how such adjustability of the camera objective would effect the illumination of the various images produced by the pyramid mirror.
SUMMARY OF THE INVENTION
The present invention provides a substantial improvement over the system shown in the German specification. More generally, the present invention provides an improved optical beam splitter arrangement which may have other applications as well as in the form of electronic high speed camera disclosed in the above German specification.
In accordance with the present invention, an optical beam splitter comprises an imaging lens assembly having a single optical axis, and reflecting means located on the image side of said imaging lens assembly and having a plurality of angled reflecting surfaces disposed at different locations transversely of the optical axis to produce a respective corresponding real image of an object being imaged by said imaging lens assembly reflected in each of said reflecting surfaces, wherein said imaging lens assembly is arranged to image a real image formed of the object by a selected camera lens assembly locatable on said optical axis and having an exit pupil located at a known distance on the object side of said real image, said imaging lens assembly being adapted to image said exit pupil of the camera lens assembly to an aperture plane located adjacent said reflecting means.
This arrangement enables the optical beam splitter as defined to be used in combination with a standard selected camera lens. In a camera lens assembly, the exit pupil of the assembly may be taken to be spaced on the object side of the image plane of the assembly approximately by the effective focal length of the assembly. The beam splitter of the present invention is arranged to operate in combination with such a standard camera lens assembly, providing multiple images reflected in the respective reflecting surfaces of the real image formed by the camera lens assembly. At the same time, the imaging lens assembly of the optical beam splitter images the exit pupil of the camera lens assembly to a plane adjacent the reflecting surfaces. As a result, the beam splitting performed by the reflecting surfaces takes place in an exit pupil of the complete lens system comprising both the imaging lens assembly and the camera lens assembly. In this way, uneven illumination and shading of the images reflected in the reflecting surfaces can be avoided. Further, the usual focusing function of the camera lens assembly can still be exploited without effecting the optical performance of the rest of the beam splitter. Aperture adjustments can be performed either at an aperture plane within the selected camera lens assembly, or at the aperture plane provided adjacent the reflecting means. As will become apparent, using an iris at the aperture plane adjacent the reflecting means gives substantial advantages in minimising shading of the reflected images.
Conveniently, said reflecting means comprises a pyrami
REFERENCES:
patent: 3601480 (1971-08-01), Randall
patent: 4167756 (1979-09-01), Smith
Hadland Photonics Limited
Lester Evelyn A.
Nelms David C.
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