I own a 30 year old Nikon FM manual focus camera and want to buy a 24mm wide angle lens. I was told this camera requires me to buy an AI or AIS lens (Indexing ?). Question 1 - Do I need to buy a lens with AI or AIS ? Question 2 - What is AIS ?

Thanks in advance.

-- Carl Gilbert (csgilbert_ny@hotmail.com), July 04, 2001

Answers

Yes, that's right, Carl. To make full use of the Nikon FM, you will need lenses using AI or AI-S metering technology ... in practice any lens made by Nikon since 1977. Earlier, pre-AI, lenses will fit the FM perfectly well, but you would have to use stop-down metering with them.

About the only Nikon lenses made since 1969 that will NOT fit the FM are those very early fish-eye lenses that go real close to the film plane and can only be used with mirror lock-up ... which the FM does not have.

Nikon SLRs have always metered at full aperture (as opposed to stopped-down). The early lenses measured the actual aperture being used by means of the "rabbit ears" that you find on manual-focus Nikkors; the camera needed to know the maximum aperture as well -- at first this had to be entered by the photographer, but later was set by doing the "Nikon twist" (running the aperture ring fully to the left then fully to the right) after mounting the lens.

In 1977, Nikon brought out AI (automatic indexing) whereby a ridge on the lens mount told the camera

• not what was the actual aperture and what was the maximum
• but how much this particular lens had been stopped down from its maximum. At the same time, Nikon brought a range of cameras that used AI, including the FM that you have. (So your camera is in fact no more than 24 years old.)

  AI-S (automatic indexing -- shutter) came in a few years later, when Nikon wanted to add Programmed exposure and Shutter-priority exposure to its cameras. With the new technology, the closing of the aperture was made directly proportional to how much the aperture control turned. This technology came out first on the inexpensive Nikon Series E lenses, and later on the AI-S Nikkor range itself. AI-S technology is indicated to the camera by a small scoop on the rear of the lens; most humans spot it by observing that both numbers for the lens's minimum aperture are orange.

  The Nikon FM uses only manually-metered exposure. It neither knows nor cares whether your lenses are AI or AI-S.

  All AF Nikkor lenses -- except the new Series G lenses which have no aperture ring -- support AI-S metering and will work on your FM. However the feel you want from a manual-focus aperture ring -- smooth but heavily damped so that the lens stays where it is focused -- is quite different from what you want for an auto-focus lens -- where you want the focus to be loose enough to be driven by a small motor. The NikonMF mailing list on YahooGroups is the (extremely civilised) home of agonised debate about the manual-focus feel of AF Nikkor lenses.

  By the way, the Nikon FM is still a cult camera among ultra-light-weight enthusiasts. Its 410g (14 oz) weight was achieved by a zen-like omission of anything inessential, rather than by cutting corners on build quality. Lenses that have the same repute are the AI Nikkor 20mm f/4 and the Nikon 100mm f/2.8 Series E; presumably the new microlight Nikkor 45m f/2.8P will join them.

  This is not in any way an attempt to dissuade you from buying a 24mm lens. Genuinely wide angle lenses have a frightening amount of foreground that has to be used. I'm still learning how to use a 24mm and am not ready to move on to 20mm yet. And besides, every Nikon user has to own a 24mm f/2.8 at some stage in his or her career!

  Later,

  Dr Owl
  
  -- John Owlett (owl@postmaster.co.uk), July 04, 2001.

You forgot the ultra-compact 45mm GN Nikkor John. ;^)
I've nothing to add to what John has already comprehensively covered, except that the 24mm f/2.8 MF Nikkor is a nice lens, and I don't find it at all scary to use. The 20mm is another matter.

MF Nikkors are now very overpriced new, and some of them most definitely aren't worth the money, including both versions of the 24mm. Thankfully the 2nd hand market is not quite so crazy.

-- Pete Andrews (p.l.andrews@bham.ac.uk), July 05, 2001.

Greetings

If you use a pre-AI (IC) lens, take care to do not breaking the small gear that connects the FM metering system with the AI lenses aperture ring. This gear is a small square that moves along the bayonet diameter, outside; and in the FM/2/n it is not retractible. It is retractible in the F4/5 for instance (I never checked Regards, Walzi

-- W. daSilva (walzi@niteroi.etc.br), July 05, 2001.

[Reposting - the above message came out truncated]

If you use a pre-AI (IC) lens, take care to do not breaking the small gear that connects the FM metering system with the AI lenses aperture ring. This gear is a small square that moves along the bayonet diameter, outside; and in the FM/2/n it is not retractible. It is retractible in the F4/5 for instance (I never checked F-F3). Check pls www.aiconversions.com to enlighten this problem.

Regards,

Walzi

-- W. daSilva (walzi@niteroi.etc.br), July 05, 2001.

The AI coupling tab flips up on the FM (although not on the FM2), allowing pre-AI lenses to be used with stop down metering.

-- Pete Andrews (p.l.andrews@bham.ac.uk), July 05, 2001.

You've got a mighty fine camera there Carl. I bought mine 24 years ago when the FM first came out but it doesn't feel that old! I also have the AI24mm f/2.8 lens and used it a lot for street and café photography at night (pushed Tri-X and HP5, ah where have the days gone...). Anyway, that is a great lens : sharp, compact and very versatile. A useful lens that, as Dr.Owl said, you cannot do without. It IS worth its money because it will last forever. Your children will inherit that lens and still use it. Good luck and good light to you!

-- benny stevens (b.stevens@jvc.be), July 06, 2001.