Additional Information on
Focusing Unit for Telephoto Lenses


Nikon Focusing Unit CU-1 & AU-1

The Focusing Unit is an intermediate tube that is placed between a camera and any one of the Nikkor 400mm, 600mm, 880mm and 1200mm super telephoto lenses. It has a focusing device and an automatic diaphragm with click-stops at f/4.5, f/5.6, f/8, f/11, f/16 and f/22. (The automatic aperture cannot be used with the 1200mm lens*). The maximum f-number on the focusing unit depends on the lens used.

Two types of focusing units - the Nikon Focusing Unit AU-1 and the conventional Nikon Focusing Unit - are available. The AU-1 unit accepts the Nikon standard 52mm filter inside the unit, and it is compact and easy to handle since essential controls are conveniently placed close to the camera body. With the conventional Focusing Unit, a 122mm filter is attached to the front of each lens. Two part telephotos use a common Focusing Mount Adaptor (B). Its principle works something like camera mounts on the lens, while the lens mounts on a tripod - the advantage of the unit is being - the entire lens rotates in its mount so you can turn the camera conveniently from vertical to horizontal or vice versa.

NO Ai Nikkor-P 600mm f/5.6 Super telephoto lens Credit: Image(s) displayed herein courtesy of all the nice folks from Taiwan's Digitize-Future@EBAY®. Some of them are extracted from their very popular online EBAY STORE. The Company also has a website on their own at Image(s) copyright © 2006. All rights reserved. Please respect the visual property of the contributing photographer.

CLICK FOR AN EXPLOSIVE VIEW(S) from Thumbnail(s) Below

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Also popularly referred as "two parts" telephoto lenses. The first series of Nikkor super-telephoto lenses with focal length from 400mm and above were designed into two sections which comprised of a focusing unit and lens head on another. The theory of lens designers (Not just Nikon, others such as Canon etc. used similar concept) thought such design can made a standard focusing unit for common use of those long super telephoto lenses with the convenience of only changing the lens heads wherever it requires without physically changing a entirely lens. CU-1, this improved mobility and especially in situations where a tripod or other film support is constantly required to hold such heavy optic. So, on the camera section, a focusing unit mounts which contains an automatic diaphragm and a focusing mechanism and it will accept individual lens heads which has the optical glass within.

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Credit: ALL Images of the 600mm f5.6 Nikkor-P with Nikon Focusing Unit displayed in this site courtesy of Ebay - Mathew Duren<<> Copyright © 2003.

* Nikon has designed two versions of the original focusing units for those older super-telephoto lenses thus far. The Focusing Unit CU-1 Model 1 and Model 2 has an integrated aperture, a gray colour wide grip ring for focusing with a tripod clamp. Main difference between Model 1 and Model 2 is the colour of the focusing grip with the latter finished in matte black. Both model 1 and model 2 has F-bayonet type Mount on the camera side and a 88mm screw-in type mount on the lens section. The longest reaching Nikkor 1200mm cannot be used in automatic aperture control via the two units.

<<< --- An array of old Nikkor super-telephoto lenses with Nikon Focusing Units (two units at the top).

However, with the introduction of the ED series of Nikkor super telephoto lens heads such as Nikkor 600 f/5.6 ED, Nikkor 1200mm f/11 ED a completely new design of the focusing unit, AU-1 was introduced to enable better compatibility with such lenses. The focusing ring of the AU-1 has a built-in aperture control from f/4.5 to f/22. Unlike the odd looking focusing ring found on earlier model(s), the AU-1's focusing ring uses a hard rubberized 5 rows rectangular texture found on late Nikkor lenses. A small lever can be screw-in near the focusing ring for better focusing control and handling. There are coloured markings to remind users to set the appropriate setting when use with lenses of different focal length. Red - 400mm, yellow - 600mm, Green - 880mm and blue - 1200mm. These are again inscribed on the distance scale in two sets of values: 400-600mm in one group and 600-1200mm in another. The tripod clamp can be adjusted swiftly for horizontal or vertical format shooting. Another improvement of the AU-1 is, it uses 52mm filters which can be inserted into the focusing unit but CU-1 Model 1 and Model 2 do not have such feature and thus, it may require the user to use 122mm filter screw into the front of EACH of the lens head. Overall, the AU-1has a much improved design and handling than earlier model 1 and Model 2 units.

400mmf56nonAic.JPG (43k) Loading ........

Three additional focusing scales are provided for 1200mm, 880mm and 600mm. Click here to see an | INSTRUCTION | how to mount the scale to the lense.

Credit: Image at left and scanned instruction copy of Focusing Unit courtesy of "Arnd Janus®" <>". Image Copyright© 2003. All rights reserved.

Each super telephoto lens comes with a removable distance scale, which can be detached or attached to the focusing unit by means of screws. A large scalloped focusing ring is easy to grip when focusing. The unit is also supplied with a shoulder strap for carrying ease. An accessory cradle for the focusing unit which provides a firm support to the total unit for smoother focusing is available on order. The tripod socket on a revolving collar allows selection of vertical or horizontal picture format while the entire unit is mounted on a tripod.

Focusing unit 400mm f/4.5 w/AU-1.gif
Comparing size and dimension of a typical Nikkor 400mm f/4.5 telephoto lens head with a companion AU-1 unit.

Model 1(Model 2) Focusing Unit in
PDF file (27k)

Specification of a Nikon Focusing Unit Model 1 (model 2):

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Mount: F-bayonet type (camera side) 88mm screw-in type (lens side)
Aperture diaphragm: Automatic (except for 1 200mm f/11 lens
*), click-stops to f/22
Tripod socket: 1/4 in. threaded; provided on rotating ring for horizontal and vertical positions
102mm dia. x 312.5mm length (4-1/32 in. X 12-5/16 in.)
1.4kg (3.0 lb)
rear cap type F ( 108 - 00 - 401), cradle for Focusing Unit (108 - 04 - 602)
Nikon Product Code No. for this item: 108-02-600

Credit: A close-up view of the Focusing Unit contributed by "Arnd Janus®" <>". Image Copyright© 2003. All rights reserved.

Nikkor Super Telephoto Lenses - | 300mm | 400mm | 500mm | 600mm | 880mm | 1200mm | Reflex - 500mm 1000mm 2000mm

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Recommended links to understand more technical details related to the Nikkor F-mount and production Serial Number: by: my friend, Rick Oleson by: Hansen, Lars Holst

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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.