• Construction of an all-sky camera

      Davis, T.N.; Elvey, C.T. (Geophysical Institute at the University of Alaska, 1955-10)
      The "All-Sky" camera herein described is an outgrowth of camera* operated in Alaska by the staff of the Geophysical Institute. The principle has been of use in cloud studies and was first used by C. W. Gar tie in for auroral photography. In its p resent form the camera is capable of recording stable or slowly moving auroral forms and is useful for synoptic "mapping of auroras and detail studies. By proper scaling methods the camera gives fa irly well defined mapping of aurora occurring within a circle of 500 km radius and along the lengths of arcs, i.e . geomagnetic East and West, to distances of about 1200 km. These radii are based on an estimated lower border height of 100 km with curved earth consideration. Since the main use of the camera will be in high latitudes where severe weather conditions occur, special effort has been made to design a rugged instrument capable of withstanding high winds and low temperatures. Ease of operation under adverse weather conditions has also been a consideration. Whenever possible, use has been made of commercially available parts to reduce construction costs. An attempt has been made to simplify the construction of those parts not commercially available. The camera is designed to be built in a shop having a d rill press, lathe, milling machine, welding equipment, and carpentry tools. The recording element is a 16 mm movie camera with a 50 mm f/l. 5 lens and equipped for lapse-time photography. The camera views the entire sky in a convex mirror. A number of cameras have been considered, two of which, the Bolex H-16 Leader and the Kodak K-100, appear best suited with respect to cost and adaptability. The Bolex H-16 is equipped for lapse-time photography and requires no modification. The Bolex has the disadvantage of only sixteen feet of film run per spring winding, hence, requires attention each ten hours if one picture per minute is to be taken. The Kodak K-100 must be modified for lapse photography but has forty feet of useful film run and will operate without attention for twenty-four hours at one frame per minute. Both these cameras may be solenoid driven which allows variation of exposure times with minimum effort. An overall view of the camera is shown in Fig. 1. Fig. 2 shows t the optical arrangement. Calculations made on the basis of Fig. 2 and the graph of height, angle, and distance, Fig. 3, allows the location with respect to the earth's surface of any point on the photographic image.