Importance

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Abstract

A borehole survey instrument is provided which includes a meniscus type floating compass member for indicating azimuth and inclination. A light source is disposed below the indicia for illuminating the indicia upwardly through the liquid in which the compass member floats and a novel lens system is provided for focusing the image of the illuminated compass member upon a film disposed below the compass member and for transmitting illumination to the compass member. The compass member is mounted on a centering post which is of minimum diameter consistent with the required rigidity and which permits high angle compass members to be utilized to indicate angles approaching ninety degrees. In a preferred embodiment of the present invention, the lens system has a refractive index closely matching that of the liquid surrounding the floating compass member to minimize reflection or refraction at the inner face therebetween. Additionally, O-ring devices are utilized as centering devices in the assembly of precision machined individual parts of the instrument in order to precisely align those parts along the optical axis of the lens system.

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First Claim