AERIAL PHOTO-SURVEYS.

Otago Daily Times, Issue 19905, 27 September 1926, Page 12

AERIAL PHOTO-SURVEYS.

COMPLICATED INSTRUMENTS. Photographic survey from the air, now so rapidly developing, places no little demand upon the optician, not merely for the very large and rapid photographic lenses used tor exposing, but also lor optical devices which insure that the aeroplane is piloted in parallel straight lines to and fro. so that every square yard of the ground below is photographed in its turn, in regular order, without omissions. To do this properly over any very large area calls for very special optica! equipment, because the course of the aeroplane over the ground may be seriously modified by the wind, and it may follow a materially different path over the ground from that indicated by the compass bearing. It is absolutely necessary for an observer to bo constantly checking the ‘‘drift” and preventing errors arising and accumulating due to wrong estimation of wind, or change in its direction or strength. To provide apparatus for carefully following the movements of the objects below, and .erifying how the aeroplane really does move over the ground, provides the optician with some difficult problems to solve, as, in an aeroplane, obstructions to a clear view abound j on every side. j In addition to the equipment in the aeroplane, further very special equipment is needed to carry out the work of making the maps from the negatives exposed from the air; projection apparatus Is required j for this of no little elaboration. British opticians arc to the fore in dealing with all these new optical problems, and this was very evident from an inspection of the exhibition of optical instruments recently held at the Imperial College of Science and Technology in London.