Additional Information on 10mm f5.6 OP-Fisheye Nikkor Lens 10mm f/5.6 OP FISHEYE-NIKKOR Originally introduced in 1968 and was discontinued eight years later in the mid of 1976. This is a highly specialized lens that offers unique orthographic projection (OP) characteristics producing a circular image of 180 degree . The image reproduced, however, is larger in the center and gradually becomes more compressed toward the periphery than the images produced by other Fisheye-Nikkors. To meet the exacting OP requirements, an aspherical front lens is employed. This projection formula provides a special configuration through which the luminance of a place is measured. When the light source is photographed with the OP Fisheye-Nikkor, the proportion of the image area of the light source to the total area represents the luminance or brightness of the place. This proportion is called the "configuration factor" or "sky factor" when the light source is the sky. This feature is effectively applied to architectural design, civic improvement, street lighting, fire safety studies and other specialized applications. The lens is also useful in advertising photography to emphasize the main subject by taking advantage of the OP characteristics. Another characteristic of the OP design is that subjects of the same brightness are reproduced with equal density, no matter where they are positioned in the picture. Therefore, even with the use of narrow latitude color film, uniform image brightness is obtained over the entire circular field. A fixed-focus lens, it requires the mirror to be in the "up" locked position before mounting. An accessory viewfinder, which can also be used on the 6mm f/5.6 Fisheye- Nikkor, is available. The lens has six built-in filters on a rotating turret. Relative: A fixed focus, preset 16.3mm f/8.0 Nikon Fisheye camera, 1960. Credit: Image courtesy of Photo_Arsenal- Worldwide® Germany. The Company also maintains an active EBAY Store, trading many used and new photo equipment of various labels. Photo Aersenal can be contacted at Photo Arsenal Boris Jamchtchik, Altenfurter Str.16a 90475 Nuernberg Germany Tel.: +49 (0) 911/ 4008081 E-Mail: ebayshop @arsenal-photo.com. .Image(s) copyright © 2008. All rights reserved. Please respect the visual property of the contributing photographer. In fact, Nikon can safely claimed producing the World's first 35mm lens with an aspherical lens elements. It covers a complete 180° hemisphere, producing a 20mm diameter circular image. With its orthographic projection formula, the OP Fisheye-Nikkor is a convenient tool for the betterment of civic environment. In city planning, for instance, it will help obtain the sky factor in evaluating the proper illumination of metropolitan districts. In fire prevention, it can be used to make studies of the extent and transmission of heat radiation from a fire. It will also help to determine the amount of interior lighting needed in environmental planning. One of the earlier application was on town planning especially on high- rise construction in urban planning. Care must be taken to avoid narrow streets thus cutting the level of illumination, both inside and outside high- rise areas. Considerable study must also be given to the effects of radiant heat, generated by fire, on adjacent buildings to give maximum safety to inhabitants. When used by urban planner and safety investigator, the lens is used to determine the quantitative luminance of an area or the effects of radiant heat by providing a geometrical configuration of the subject image. The OP-Fisheye as well as the Fisheye 7.5mm and 8mm lenses covers an angle of view of 180°. But this lens is designed on an orthographic projection formula, from which the "OP" designation is obtained. Some other older version of Nikkor Fisheye lenses were also designed on equidistant projection formula. The difference between orthographic and equidistant projection formula is expressed in the following: Equidistant Projection: Orthographic Projection: Y: Distance of image point from picture center 0: Zenith angle C: Constant The construction of the OP Fisheye-Nikkor has been accomplished by use of an aspheric front element to meet the exacting requirements of the orthographic projection formula. When it is required to measure luminance of a certain area, it is easy to use a photometer. But the data obtained by such measurements cannot be utilized objectively to compare the luminance at different places or to evaluate the illumination of an area because of dependence on season, time and weather. This being the case, it is more convenient to use, instead of the intensity of illumination, the configuration factor. When an area of light is measured in a picture made with the OP Fisheye, it is proportional to the illumination of the plane parallel with the film surface. The configuration factor is the ratio of this area to the total area of the picture. In other words, the proportion between the total area pictured and the light source is termed the "configuration factor." When the light source is the sky, the configuration factor is called the "sky factor." In pictures 1 and 2, the sky area to the total area photographed is about 48% and 39% respectively, with the sky (configuration) factors 0.48 and 0.39 respectively. Thus the luminosity of the former is greater than that of the latter. In a photograph taken with an OP Fisheye-Nikkor, objects of the same luminance are pictured with the same density regardless of their position in the whole picture. This is attained by the orthographic projection formula and is especially useful for measurement of sky light distribution. And even with the use of narrow latitude color film, uniform image brightness over the entire circular field is obtained. In use with early Nikon F camera, the OP Fisheye Nikkor lens is mounted after the viewfinder mirror has been placed in the up and locked position. CLiCK on thumbnails for an ENALRGED VIEW Credit: Images courtesy of Adorama® Inc. "Ebay - Mathew Duren" <ebay@adorama> Webisite URL: Adorama.com, who also operates a popular Ebay Store. All images appeared herein are Copyright © 2003. All rights reserved. Please respect the visual property of the contributing photographer. Most people may not see the immediate benefit the lens would bring to general photography. Besides, just like any other older versions of Nikkor Fisheye lenses, the protruding back of the lens also restricted those Nikon SLR cameras which does not equipped with Mirror Lock Up feature to use them freely. Anyway, it is not a day to day photographic lens and for some of those who has the specific interest, it has even turned into a collectible. I am not so sure how the lens used with the Nikkormat which has their accessory show on top of the pentaprism. An optical viewfinder with a 160° angle of view is mounted on the camera body accessory shoe for viewing. Six filters are built into the lens in a turret which is rotated easily for the necessary filter. The lens is fixed focus since its extreme depth of field covers from infinity to one meter even at full aperture. Specifications: Focal length: 10mm Maximum aperture: 1:5.6 Lens construction: 9 elements in 6 groups (Aspherical front lens element). Picture angle: 180°; Projection formula: Orthographic Image size on film: 20mm in diameter, Focusing: Fixed focus Focusing screen recommendation: NONE as Mirror is lock up. Aperture scale: f/5.6- f/22; Aperture diaphragm: Manual Attachment size: 79mm (P=0.75) Filter: Built-in, L1A, Y48, Y52, 056, R60 & X0. Filter L1A for color and B/W; all others for B/W only. Dimensions: 84mm dia. x 105mm length (3-5/16 in. X 4-5/32 in.); Weight: 380g (13.4 oz) Accessories: 79mm screw-in front cap (109 -00-179), rear cap type 3F (108-03-400), leatherette case CL-4 (108-03-303), fisheye finder (108- 03-500) Although it is not applicable anymore,Nikon Product Code No. for this lens: 108-03-110; Note: Production Serial Number believed to have started from 188001 for this non-Ai-Spec lens. Source: Nikon Hand Book. 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