AI 24mm f2.8

Ever since Nikon introduced AI back in 1977, all versions of Nikon's 24mm/f2.8 have exactly the same optical formula. In other words, the AI, AI-S, AF, and AF-D versions all have CRC. The coating may be a bit different over time, but the optical formula has not changed in 3+ decades. That is partly why even the latest 24mm/f2.8 is not that great a lens any more.

As Shun noted, all versions of the 24mm f/2.8 have CRC, specifically via the rear group. If you look at the rear element of the Nikkor 24/2.8 (any manual or AF version) as you focus it, you'll see that the rear group rotates with focus on a secondary helicoid. Compare that to any other unit focusing Nikkor prime without CRC, say the AF-D or AiS versions of the 50/1.8 or 50/1.4, and you'll immediately see the obvious difference (no rear element rotation).

I have an old Ai lens Brochure of Nikon's and in that the 24mm f/2.8 is listed as having CRC. The date of the brochure is 1979.

The first Nikkor-N 24/2.8 from late '60s had CRC.

The 24/2.8 AiS is perhaps not stellar on FX cameras, but does more than adequately on such cameras as D700, D3/3S, and D3X. I use it a lot for IR with D200 and suchlike cameras as well.

I have serious doubts that all versions of Nikon's 24mm/f2.8 have exactly the same optical formula. I used to own an earlier copy of the AI version and at one point I wanted to upgrade to the AF-D version. I did a brief test with a borrowed AF lens and my MF copy was superior especially wide open. Of course you can't be sure when testing just a single copy of each version but the difference was quite visible on D700.

The original 24mm f/2.8 Nikkor c. 1967 was in fact the first Nikon lens with CRC. There has never been a non-CRC version of that lens, either in manual focus or AF.

According to Roland Vink's site, the formula changed from 9 elements in 7 groups to 9 elements in 9 groups when the AI version came out in the late '70s. After that it remained stable. This doesn't necessary mean there were no changes at all to the formula after the '70s (there are a lot of different ways to use 9 elements in 9 groups), but I don't know of any reason to think that there have been any significant changes since then other than AF and perhaps some improvements in the lens coatings. From the outside, aside from cosmetics, they all look very similar.

Mihai, I've also noticed that supposedly "same formula" lenses in MF are often superior to the AF versions. I put this down to sloppier construction in the AF lenses, with greater use of plastics and looser tolerances to make the focusing freer. Or maybe both you and I have simply been unlucky in the AF lenses that've come our way?

Thanks to all. Answers appreciated. I am currently thinking I will add the 24mm to my bag, but also considering the 20mm f3.5. If anybody would like to take this thread for a slight turn, I would appreciate feedback on this as well. Is there really a big difference other than 20 vs 24?

Charles,
I have and use and like both - the 24/2.8 AiS and 20/3.5 AiS.
The 20/3.5 AiS is a lens with really strong vignetting - I have to stop it down to f8-11 to get pretty even skys. Sharpness and contrast in the corners are not very good from f 3.5-5.6. It's better in terms of flare and ghosting than the 24/2.8 AiS.
The 24/2.8 AiS is also a strong vignetting lens, but not so extreme like the 20mm. Corner contrast and sharpness are better in the 24mm, but flare and ghosting are a weak point of the 24/2.8 AiS.
I use both lenses with a D700 and from time to time wide-open to use the vignetting as an effect.
The 14-24/2.8 easily outperforms the classics, but not everybody likes the bulk, weight and price of this outstanding zoom.