Additional Information on
45mm f2.8 GN (Guide Number) Auto Nikkor Lense

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45mm f/2.8 GN Auto Nikkor(1969)

Introduced along with
Fisheye-Nikkor 6mm f/5.6 around in 1969. The GN Auto Nikkor is designed to simplify flash photography. As its name GN (guide number) suggests, the lense employs the guide number coupling system for automatic diaphragm adjustments. With any ordinary lense, aperture size must be changed for each different shooting distance with flashbulbs or non-automatic mode in an electronic flash. You must also calculate aperture size for each shooting distance, using the guide number equation with the flash unit that you are using.

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Before the popularity of the automatic feature in an electronic flash, these calculations for precise f-number can be troublesome. The GN Nikkor has a control that set for the guide number of the type of flashbulb or non-auto flash (even flashbulb) you are using. After setting is done - you just focus. By presetting the flash guide number on the lense GN (guide number) scale from 10 to 30 in meters and 32 to 250 in feet, the lense diaphragm is coupled to the focusing ring. This automatically adjusts (stops down or opens up) the aperture in relation to the focusing distance, providing reasonably good flash exposure at all subject distances (i.e. aperture is mechanically connected to the focus control so when you focus closer, aperture is automatically closed down). This frees the photographer from the trouble of calculating the correct aperture and readjusting the lense diaphragm.

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Is this simply a flash-specific lenses ? What if you are not using a flash ? When the GN control is disconnected, the lense acts like an ordinary compact 45mm standard lense. By disengaging the GN coupling device, the lense can be coupled with camera exposure meters for full aperture exposure measurement and used as an ordinary normal lens. The 7-bladed polygonal diaphragm, designed to form an almost circular aperture around the most commonly used f/8 setting, reduces the effects of light diffraction to the minimum. It can be stopped down to f/32.

Credit: Images courtesy of Lizardtracer®"URL: All images appeared herein are Copyright © 2003. All rights reserved. Please respect the visual property of the contributing photographer.

Light and compact, the lense weighs only 150g (5.3 oz) and protrudes only 20mm (3/4 in.) from the camera body. When used in combination with a Nikon Speedlight Unit, the GN Nikkor lense can be particularly effective for capturing a moving subject or for candids where the photographer has no time to reset the diaphragm. The GN Auto Nikkor may also be used as a substitute for a normal lense for general photography. Its "normal" picture angle of 50° and moderately fast f/2.8 maximum lense aperture makes it very useful for general photography especially when most flash units should have the angle of field well covered.

At the time of its introduction, many camera manufacturers were trying to provide a solution for flash photography. While the Nikon's experimental one was a lens-control system, others such as Canon has an almost similar way in their CAT flash system, a semi-auto way in controlling auto flash, first seen in their flagship model, Canon F1 (1971-1981). The main advantage of the CAT system was - the coupler enables the semi-auto flash system works on many of their FD lenses instead of a specialized designed lenses such as the GN Nikkor here. Anyway, neither of the companies have pursued further in their respective research because none were comparable to features found in a typical automatic flash. The GN Nikkor solely represents a stage of development at the course of Nikon SLR research and the design was short-lived and never evolved further into a mainstream system for auto flash photography.

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Credit: A few of the images appeared here at this section courtesy of Emanuele "ebay-camera$®" <> who operates a popular Ebay Store. All images appeared herein are Copyright © 2003. All rights reserved. Please respect the visual property of the contributing photographer.

The distance scale and guide-number scales are engraved in yellow (feet) and white (meters). In combination with an extension ring or a bellows, this lens is also highly effective for close-up photography because it has relatively little image deterioration even in high magnification ranges.

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Focal length: 45m
Maximum aperture: 1:2.8
Lens construction: 4 elements in 3 groups
Picture angle: 50° at infinity
Distance scale: Graduated both in meters and feet up from 0.8m and 3.0 ft to infinity (
Aperture scale: f/2.8 - f/32

<<< -- Credit: Image courtesy of Mr. Joe <>. Image copyright © 2003. All rights reserved. Please respect the visual property of the contributing photographer.

Aperture diaphragm: Fully automatic
Meter coupling prong: Integrated (fully open exposure metering)
Attachment size: 52mm (P=0.75); Filter: 52mm screw-in
Hood: HN-4; Weight: 150g (5.3 oz); Dimensions: 64mm dia. X 31 mm length (2-17/32 in. X 1-7/32 in.)

Accessories: 52mm Snap-On front cap (108-00-400), rear cap type F (108 -00 -401), 52mm screw-in lense hood (108 -03 -200), plastic case type S (108-00-300); flexible pouch No. 51 (108-00-302). Although it may not be applicable anymore but Product Code No. for this lense: 108-03-111

Credit: Images courtesy of MC Lau® <>. Image Copyright © 2003. All rights reserved. Please respect the visual property of the contributing photographer.

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Credit: MCLau®, who has helped to rewrite some of the content appeared this site. Chuck Hester® who has been helping me all along with the development of all these Nikon websites; Lars Holst Hansen, 'Hawkeye' who shares the same passion I have; Ms Rissa, Sales manager from Nikon Corporation Malaysia for granting permission to use some of the official content; Ted Wengelaar, Holland who has helped to provide many useful input relating to older Nikkor lenses; Some of the references on production serial numbers used in this site were extracted from Roland Vink's website; Hiura Shinsaku from Nikomat Club Japan. Lastly, to all the good people who has contributed their own expeience, resources or kind enough granted permission to use their images of their respective optic in this site. It is also a site to remember a long lost friend on the Net. Note:certain content and images appeared in this site were either scanned from official marketing leaflets & brochures published by Nikon and/or contribution from surfers who claimed originality of their work for educational purposes. The creator of the site will not be responsible for may discrepancies arise from such dispute except rectifying them after verification. "Nikon", "Nikkormat", "Nippon Kokagu KK" & "Nikkor" are registered tradename of Nikon Corporation Inc., Japan. Site made with an Apple IMac.