US 6,476,979 B1Granted

Focusing systems for perspective dimensional measurements and optical metrology

OwnerDavid F. Schaackinventor

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Abstract

Focusing systems for which variation of magnification with focus is either inherently compensated, or is calibrated and corrected. The required conditions for inherent compensation are determined, and the desired state is called constant relative magnification. It is shown that telecentricity does not guarantee constant relative magnification. Both telecentric and non-telecentric accessory cameras for endoscopes are disclosed that have constant relative magnification, as are additional optical systems for general metrological purposes. Methods for calibrating change in relative magnification and deviation of the optical axis with focal shift are disclosed, as are methods for incorporating these changes into perspective dimensional measurements. Embodiments are disclosed in which only a single quantity need be measured to perform the correction, and these embodiments require only a low-resolution position transducer to provide accurate measurements. Apparatus is disclosed that enables an accessory camera to be aligned to an endoscope using only externally accessible adjustments. This apparatus also makes it possible to de-mount the camera from one endoscope and re-mount it to another without requiring any recalibration.

Claims11

Dependent claims

A non-telecentric optical system comprising at least one optical element, an aperture stop, and an image viewing plane, said optical system having an optical axis, a focal length, a focal state, an entrance pupil, a first principal plane, and a second principal plane, wherein each of said at least one optical element, said aperture stop, and said image viewing plane has a position along said optical axis, and wherein each of said entrance pupil, said first principal plane, and said second principal plane also has a position along said optical axis, wherein said focal length and said positions of said entrance pupil, said first principal plane, said second principal plane are determined by said positions of said at least one optical element and said aperture stop, wherein adjustments are provided for changing said focal state, said adjustments controlling the positions of said at least one optical element, said aperture stop, and said image viewing plane, wherein said adjustments are adapted to fulfill the following conditions:

(a) the position of said entrance pupil is constrained to a substantially fixed position along said optical axis;
and
(b) said focal length and said positions of said first and second principal planes and said image viewing plane are constrained to substantially satisfy the equation:
z pp1 + ( 1 - ( z pp1 f ) ) ⁢ ( z ivp - z pp2 ) = K crm
where f represents said focal length, zpp1 represents the position of said first principal plane, zpp2 represents the position of said second principal plane, and zivp represents the position of said image viewing plane, where Kcrm represents a constant value that does not vary as the focal state of the system is changed, and where the zero reference for position is at said entrance pupil.

2 more elements

Dependencies are inferred from the claim text.