its height about 0.7 cm (ratio of 1.86). Finally, the dome to disc width ratio was 4.38 and the dome to disc height ratio was 2.29. While these ratios are a function of the viewing aspect angle, they may, in general, be compared with corresponding values given elsewhere (Haines, 1978, 1979) of similarly shaped aerial objects of unknown origin that have been reported over the years. This previous work shows that the present photographic image of a disc is not uncommon; there is a larger context of purported UFO drawings into which this object fits.

The hyperfocal distance is the nearest distance from an object being photographed to the camera at which the object is in sharp focus when the lens is focused on infinity. Since the mountain is in sharp focus and the photographer said that she took great care to manually focus the camera it is possible to determine the hyperfocal distance by also knowing the focal length of the lens and its aperture (Neblette, 1965). For a 50 mm focal length lens and f-11 aperture the hyperfocal distance is 15 feet. Corresponding distances for f-8 and f-16 apertures are 20 and 10 feet, respectively. Thus, the airborne object in question must have been farther than ten feet (and probably farther than 20 feet) from the camera since it also was in sharp focus.

The actual camera settings used can only be inferred. A film with an ASA 100 exposure index (as this was) and a lens with the optical quality of this one would have very likely automatically pre-set a shutter speed of 1/125th second at an aperture of f-11 for the ambient scene luminance which was present.

Finally, the negative was in very good condition and did not have any visible scratches, major blemishes, or other defects. An invisible vertical scratch was noted in one of the dye layers as will be described later, however, this scratch was well away from the disc image.

The Camera and Lens

The camera was a Mamiya, model 528AL, single lens reflex (SLR) type with permanently attached Mamiya/Sekor 48 mm lens with 1:2.8 aperture. The serial number on the lens was M197535. The camera is of the automatic exposure type meaning that all one needs to do to take a photograph is insert the film, pre-set the correct ASA number for the film used on the camera, aim and manually focus the lens for best focus, and press the shutter release. Both shutter speed and aperture adjust automatically for "best" exposure. The shutter actuation lever is of the standard top-mounted type which requires a downward finger depression. Once the shutter has opened and closed another exposure cannot be taken without first advancing the film to the next frame. The author borrowed this camera and took a series of photographs with it under closely similar sun angle, sky brightness, and other conditions to check on possible lens and/or shutter related image artifacts. None were found. The lens was coated with the standard anti-scattering material. No scratches or other flaws could be seen in the lens elements or surface coatings.