Additional Information on
2.1cm f/4-16 Nikkor-O

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Nippon Kogaku KK / Nikon F-mount 2.1cm f/4-16 Nikkor-O, (1959-1967)

Designed by Mr. WAKIMOTO, Zenji (1924 - 1996), a highly respectable Japanese lens designer who designed the famed Micro-Nikkor series of lenses. The Nikon Japan official site has a very detailed website that featured this RF lens in relation to the background and history. Unlike the common 20mm Nikkor ultra-wideangle lenses that we are so familiar with today, this Nikkor lens has a protruding rear section which extends beyond into the lens mount and it was probably the one Non-Ai Fisheye-Nikkor lens that needs a Mirror Lock Up mechanism on the camera in order the lens can be used for photography.

21mm f/4 from NikonJP.jpg Finder.jpg
As rangefinder cameras do not have a reflex mirror inside, so even if the rear section of the lens extend all the way backward to almost reaching the film plane, it is still okay to have such design. But it is NOT the case if you want to use it with a typical SLR camera where the reflex mirror stands in its way for the purpose of providing a projected image through the lens for viewing/focusing and picture composing. Naturally, it will need an applicable SLR camera that has mirror lock up feature in order this can be used. As the viewfinder will be black out once the mirror is locked at upward position, the lens is supplied with a companion auxiliary finder that roughly give you a viewing guide for framing and picture composing.

UPDATED:- Nikon Rangefinder version, the (RF) Nikkor-O 1:4 f=2.1cm lens
* Image downloaded from Nikon Japan. I hate to use other's but I ought to as I don't have one to use here; Mail me yours to replace this. Appropriate Credit will be given.

This lens, was originated from the design that was supposedly meant for the Nikon rangefinder cameras and it was almost replicated in similar fashion with a F-mount for it be used with the Nikon F, Nikkormat and Nikon F2 series bodies. However, the lens was quite difficult to be used as it was designed to fit both the rangefinder and reflex cameras at the same time. This lens has a unique optical design (eight (8) elements in four (4) groups, with the two inner three(3)-element groups sandwiching the iris (see below) which seemingly like a Zeiss Biogon lens type. Many Nikon faithful believe this design has a more superior optical performance over the retrofocus design introduced at later stage and thus, it has slowly grown to become a collector's favoutite piece. This 21mm Nikkor lens was believed only available in black paint version and all lenses produced in this series were not coated or simply was plainly treated with singular lens coating (but I have seen some images published in some Japanese collectors' website that some looked as if they are coated lens.

image.gif 25mmf4.0.jpg
Also check and compare the W-Nikkor 2.5cm f/4.0 . Picture Courtesy of
Downloaded from Nikon Japan...  
The optical formula of the 2.1cm f/4-16 Nikkor-O featured here is very different from the retrofocus design used in the current range of Nikkor wide or ultrawides. However, unlike the Nikon F and F2, the Nikkormat series may have problems using this version of the lens. What was the problems ? Probably the Nikkormat has a different kind of accessory shoe which rest on top of the pentaprism while both the Nikon F and F2 have side-mounting accessory shoe which the lens was originally catered for and prohibiting the Nikkormat to mount and use it precisely with the center position.
Actually, if Michael has not been vanishing from this planet, he might be able to answer some of my doubts here as I recalled that he mentioned that he owns one of this lens himself. As this lens needs MLP to use and usually it carries with a high premium even as used item, it is not very viable for you rush to buy such a lens unless you are aiming to get one for your personal collection and/or investment. * Note: even the MLP capable Nikon F5 needs to replace the lens mount section in order to use any older non-AI optic.

21cm.jpg by Matthew Lin (52k) Loading ...


Credit: Both images of this old Nikkor-O 2.1cm f/4.0 ultrawide courtesy of Mr. Matthew Lin® <> with a website on his own at: Matthew is a collector for Nikon photo gear. Here are some basic info and user experience compiled by Michael Liu and I reproduced it for your reference:

Optical Construction: 8 elements in 4 groups 92 degrees angle of view; Length: 2.54cm (1"); weight: 135g; focusses to 0.9m; 52mm accessory size Note: Came with accessory viewfinder, requires mirror Lock-up and lens mount tab (only on F and F2); S/N 225001 and above for Nikkormat models; hood is now rare and difficult to find, but modern-day HN-14 (20f/4) hood seems to fit without vignetting Lens Hood $5.25 list (1967); Viewfinder $26.00 list (1967); Lens Case $5.00 list (1967); $209.50 list including finder (1965); $199.50 list (1967)

Nikkor-O 2.1cm f/4 (1:4 f=2.1cm) F-Mount version The rear lens mount section of the Nikkor-O 2.1cm f/4 F-Mount version
Credit: Image(s) courtesy of Rokas Kundrotas®. where he is more well known as maintaining another popular Rokas Photo & Videao @ EBAYwith another personal site at - both kept a huge inventry for many used collectible equipment of major camera labels. Image copyright © 2008.

Nikkor-O 2.1cm f/4 (1:4 f=2.1cm) F-Mount version front view
"..... How do I mount that #%@$ 21f/4 ? The 21f/4 is one of those oddball mirror Lock-up lenses. In addition, the rear element is not completely circular -- it started off being round, but then Nikon decided that they had to take a sliver back, so that they could clear the back of the mirror as you put the lens on. Of course, if you can't take the rear cap off, all this is moot. Because of the un-round rear element, the lens has an additional prong to make sure that the lens is oriented in the right direction. Because of the prong, which happens to overlap one of the three bayonet "teeth", you can't just flick the rear cap on and off as is usual. Assuming that your lens has been stored at infinity focus, you need to turn the lens itself so that the focus mark is not at the infinity focus mark -- I'm not sure where it ends up (maybe around 3 feet or so?), but you need to do this so that the additional prong lines up with one of the bayonet teeth -- then you can lock up the mirror, put the lens on, and shoot away with great delight. By the way, as far as I know, the F and F2 are the only Nikon bayonets that will take the 21f/4, as their mounts contain the proper tab to engage the extra prong -- other cameras, including the F3, do not have it. So, should you decide to spend $1000 US on an obsolete (single coated but superb, small, and symmetric) wideangle, plan on budgeting another $100-300 for a nice F or F2......". - Michael Liu -

NOTE: Serial Number for this version was believed to have been started with 621001 - Alternate version of the Nikon Rangefinder (RF) Nikkor-O 1:4 f=2.1cm lens (New)

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Manual Focus Versions:- | Auto-Nikkor 20mm f/3.5 UD | Nikkor AI & non-AI 20mm f/4.0 | Nikkor 20mm f/3.5 (AI & Ai-S) | Nikkor 20mm f/2.8 | AF & AF-D Nikkor Additional info on: 2.1cm f/4.0 Nikkor-O & Rangefinder version of 2.1cm f/4 Nikkor-O Relative - Autofocus Nikkor lenses / AF Nikkor 20mm f/2.8s / AF Nikkor 20mm f/2.8D ultrawideangle lens

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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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Co-developed with LARs.Gif Denmark , Creator of the Nikon Repair Group Mailing-List; A contributing effort to Michael Liu's Classic Nikon SLRs and Nikkor optic site.

Credit: To all the good people who has contributed their own experience, resources or those who are kind enough granting us permission to use their images appeared in this site. Mr. 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;LarsHolst 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; TedWengelaar,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; HiuraShinsaku from Nikomat Club Japan. t 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, sales manuals or publications published by Nikon over the years 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.