Shadow probe

A borescope having a compact imager head comprising:

• an elongated cylindrical housing having a given wall thickness, a diameter (D), and a longitudinal axis;
• said housing having a circular end face at its distal end that forms an angle .theta. with a plane perpendicular to said longitudinal axis, said angle being less than 90.degree.;
• an illumination window and an optic window mounted adjacent each other along a diameter of the end face;
• an imager having a flat recording surface, said imager being mounted behind the optic window to view a target image outside of said housing, said recording surface being parallel with said end face, said imager being positioned a predetermined distance behind the optic window to establish a region behind the illumination window of a shape and size to accommodate the distal end of a light carrying fiber bundle for illuminating a target within the viewing range of the imager without interfering with the target image;
• shadow generating means associated with said light carrying fiber bundle to produce a contrasting shadow in a target plane;
• display means connected to said imager for viewing and measuring the target image and a shadow image in the target plane;
• and
• measuring means for measuring parameters of the target image and the shadow image on said display so that the attached size of the target can be determined, wherein the diameter (D) of the imager head is substantially expressed by the relationship D=cos .theta.(OW+IW+2t);
• where:
• OW=the length of the optic window along the diameter of the end face;
• IW=the length of the illumination window along the diameter of the end face;
• and
• 2t=twice the wall thickness.