AI superior to AI-S?

[Bjørn Rørslett]

Few - if any - would consider K.Rockwell to deliver reliable information or be a 'reference'.

Some AI lenses do have CRC, yes, that has been known for a very long time. For example, 24/2, 24/2.8, 28/2, 35/1.4. However, one has to realise CRC is not just something one can add to an existing lens, the optical design has to be designed with CRC from the onset and in those early days with little or no computer assistance, this entailed long and gruelling efforts. The models I listed fall in this category. They had CRC in the initial design.

No reliable source documents the 28/2.8 AI had CRC at any time during its production run, comprising 150 - 200 thousand units. Adding CRC would entail computing the lens all over again, and retooling for its production. Which is what Nikon did when the 28/2.8 AIS with a new optical design, much improved near limit, and CRC, was launched.

[Erik Lund]

When I read:

However, Nikon's CRC system was not incorporated into the design yet and that was not until the late Ai or the Ai-S version in 1981, such feature was incorporated

I see the statement stated as an uncertainty : or like if he is not sure,,,

Otherwise it would have benn stated like this: and

However, Nikon's CRC system was not incorporated into the design yet and that was not until the late Ai and the Ai-S version in 1981, such feature was incorporated

BTW: Easy to see from the repair manual for the specific lens - They are not serial # specific,,,

[chambeshi]

Simon Stafford's most recent edition of 'The Nikon Compendium' is a useful reference on the successive models of Nikkors, summarizing practical experience in performance of some models.

He also makes a point of stating which lenses benefited from CRC. Albeit, one has no leaders to the authorities for this information.

[Bjørn Rørslett]

The solution is opening up a lens and have a look inside .... Every Nikkor appears to have its own twist to the internal mechanical design. There are common approaches, but usually they are tweaked for a given lens series. I have looked into hundreds of these lenses over the years and never cease to be amazed of their constructional diversity.

These lenses are nearly always mass production items and as such don't change much, if at all, over time within a production run. Any change might be swapping a particular screw type for another or alter the engravings on the outside. Improvements in coating tend to be visible by the change in reflected colours.

[Erik Lund]

Peter Braczko: The Complete Nikon System;

1981 Completely new construction for convertion to Ais: Now it had eight elements, CRC,,,,

All fits with all other references. So We can put that to rest

[Roland Vink]

If CRC was implemented in the AI 28/2.8 during production, the lens would have a different optical design. This is not a change which would happen silently, it would be launched as new model with closer focusing ... but all AI 28/2.8 manufactured right to the end focus to only 0.3m.
Also, I think lens catalogues during that period did mention if a lens had CRC - it was a desirable feature. It's certainly listed on the current Nikon website.

As for whether CRC acts on the front of rear group, I could add it to my database ... my question is what use is this information?
The primary function of CRC is to improve optical corrections over a wider range of focus distances, by altering the spacing between groups of elements. Whether the floating group acts on the front or rear is not relevant optically, you could build the same lens either way as long as the change in spacing between groups is the same.

It's really a question of mechanical design, for some reason Nikon chose to make the rear group floating in some lenses, for others the front group. As Eric mentioned, the front CRC may be more easily damaged by knocks. I have wondered if the front-CRC lenses might be more vulnerable to dust entering the lens since there is an open space between the front element and filter ring, although I see no evidence of this so far.

If I were to classify lenses by front or rear CRC, how do I classify the AIS 55/2.8 micro? Neither the front of rear group rotate like the wide-angle lenses with CRC, they are just move forward and back on focus helix with different pitch. I suppose the front group is attached to the upper barrel so the rear group is floating?

What about the AIS 105/2.8 micro? This has three groups - a fixed rear group that acts as a teleconverter, and two groups at the front with CRC. Is this an inner CRC lens? The AF micros also have quite complex designs ... actually the AFS micros don't have CRC at all, they use IF focusing which is also a form of floating elements that acts similar to CRC...

My feeling is that classifying CRC will lead to more confusion than it's worth ... but I am open to suggestions.

[pluton]

It is important to know if the lens has CRC of any type.
On the issue of denoting how the CRC is implemented, I agree with Roland: Merely denoting front or rear CRC doesn't cover all the technical implementations.

[Erik Lund]

I would call it FLE like we do for Leica, Floating Lens Elements.

But yes, not sure if you should add it,,,

BTW durability of the front when changing filters etc also takes it's toll on some of the CRC-F lens! Micro Nikkor 105mm 2.8

[Roland Vink]

CRC has been the Nikon terminology for floating elements for decades, and my site does list Nikon lenses ...

The front group of the AIS 105/2.8 micro is directly attached to the upper barrel, so technically it is the group behind that floats... but as Eric says, that still does not guarantee durability ...

[Bjørn Rørslett]

Front or rear CRC designation will do. The actual details in the implementation vary between the lenses and no need to delve deeply into those.

I can, unfortunately, confirm, that the 105/2.8 Micro AIS has a CRC design that makes it quite susceptible to wear and tear.

[Akira]

I would doubt the necessity of adding the info on the difference of the types of CRC in Roland's list.

When the manual focus lenses were made, CRC was relatively new technology.  The additional notion of CRC made sense to separate different versions of lenses of the same focal length/speed designation, most notably Ai28/2.8 and Ais28/2.8.  Also, it is interesting to know when the new technology was employed.

On the other hand, the modern lens designs are more complicated.  The rear focus designs like those of AF-D 85/1.8 and all of the current AF-S f1.8 and f1.4 wideangles double as CRC.  All the IF designs of tele lenses doubles as CRC.  The modern zoom lens designs triples as focusing, zooming and CRC.  So, even specifying whether a has CRC would make no sense anymore.

I don't think there were lenses of the same focal length/speed designation whose CRC was changed, say, from CRC-F to CRC-R during the MF era.

Considering that Roland's list is for separating different versions of the "completed" lens by the serial number, any addition of the info to the list would be unnecessary.

[Erik Lund]

CRC has been the Nikon terminology for floating elements for decades, and my site does list Nikon lenses ...
,,,,

I was suggesting to call it CRC-FLE for all of the lenses where it is not a group,,,    


Never mind. Leave it out.


For some of us there are more to these data than just to tell the apart for identification,,,

[Akira]

For some of us there are more to these data than just to tell the apart for identification,,,

Well, I consider Roland's list to separate the lenses without taking them apart... 

[David H. Hartman]

Few - if any - would consider K.Rockwell to deliver reliable information or be a 'reference'.

Ken Rockwell's site is a good place to get ideas but a bad place to make a buying decision. The quality of the information varies. Some times he contradicts himself. Some information is out of date. Some is superficial. Some is just wrong. If something is interesting my advice is get a second opinion from a more reliable source.

An example of a situation where I became interested in a lens at Ken's site is the 50/1.2 AIS. I liked what a read so I checked Bjørn's old site. The review there gave me the confidence to place an order. Two more lenses I became aware of a Ken's site are the AF 28-70/3.5-4.5D and AF 35-105/3.5-4.5D Nikkors. The are small and discreet. The bang for buck at $100.00 (USD) or less is great. I find them good enough for a D800. Before placing an order I got an opinion from a more reliable source.

Dave Hartman

[John Koerner]

Few - if any - would consider K.Rockwell to deliver reliable information or be a 'reference'.

Ken Rockwell's site is a good place to get ideas but a bad place to make a buying decision. The quality of the information varies. Some times he contradicts himself. Some information is out of date. Some is superficial. Some is just wrong. If something is interesting my advice is get a second opinion from a more reliable source.

Another mistake.

Ken Rockwell was the individual who agreed with every point Bjørn made (no CRC, not marked, have to actually look at the lens).

It was actually the MIR site that provided the quote that late AIs would have the CRC.

I doubt there's anyone here who's not referenced the MIR site. Again, the author may be mistaken, happens to all of us, but MIR has an extensive database of articles and history, so they also might know some things most don't.

Truthfully, the real folks to ask would be someone in Nikon's senior engineering. I was looking at the article in Nikon's 1001 Nights, and wondering if Kouichi Ohshita (the author) or Daijiro Fujie (the actual designer of the Ai-S) are reachable by the public. Would probably be the best way to resolve the question, than by speculation. The 1001 Nights article hints at the evolution from one to the other:

• "It was important that our Nikkor lenses offer clearly superior performance than Series E lenses. This is how optical design of the 28mm lens was renewed. Mr. Daijiro Fujie was put in charge of design.
  ...
  When Mr. Fujie, who loved photos and photography, was put in charge of renewing the 28mm lens, it is certain that the idea of differentiating the lens from others through its minimum focus distance came to him quite naturally. Making a wide-angle lens the most "approachable" lens (the lens with the shortest minimum focus distance) would enable differentiation in brochure specifications from the Series E lens with the same focal length and maximum aperture, and make it “the one and only” lens that would be popular for a long time to come. After two goes at trial production, the AI Nikkor 28mm f/2.8S was released in 1981."