The closed circuit television (TV) system is a well known technique for the viewing of remote objects in hostile surroundings such as high pressure environments such as the exterior of a deep diving vessel or in certain high pressure processes. The closed circuit TV system, however, requires substantial power which may be impractical in remote environments of deep diving vessels and in addition requires an expensive high pressure containment for the television transmitter, as well as associated cables and connectors through pressure vessels. In particular, wide bandwidth low signal level connections through pressure vessels are complicated. In addition, the weight of the television transmission and receiving equipment, as well as the volume loss in confined spaces makes such systems less than ideal. Where several scenes within the high pressure environment are to be viewed, plural television monitoring transmitters must be employed greatly increasing the disadvantages in cost and weight of the TV system. Where color is also desired in the closed circuit TV system, an additional complexity in cost, bulk, and transmission bandwidth is present.
There exist other applications for remote viewing where the hostility of the invironment places restrictions on the use of closed circuit TV systems as to greatly increase their cost and complexity. One example includes visual monitoring of objects in an environment exposed to intense radiation such as radio frequency interference that would require full shielding or more complex protection of the electronics and cables in the closed circuit system.
An alternative to the closed circuit television system would be to employ an optical periscope incorporating one or more series of lens trains which could transmit an image directly from the external environment to a viewer without intermediate electrical processing and would provide an optical quality substantially superior to that obtainable with television. Such optical periscope systems, also occupy a substantial volume, require a precise rigid alignment for accurate picture rendition and are correspondingly likely to be costly, particularly where a large number of widely separated scenes are to be viewed.