Floating what?

[lars_bergquist]

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This is a nit-picking, pedantical posting by a nerd obsessed with language (occupational disease: A working life as a lexicographer/encyclopedist).

 

First came floating elements: One single un-cemented optical element that moved differently from the rest of the optical assembly during focusing. First introduced in the late 1970's, as I remember, to improve extreme close focusing in macro lenses.

 

Then came floating groups. They still call them "floating elements" but they are composed by two cemented elements, i.e. a group. The first Leica example was the 50mm Summilux ASPH. Leica do not have any example of a lens with a floating element proper, that is, a single element.

 

Progress marches on. With the 35mm Summilux ASPH, new version, it is no longer even a single group that moves. It is the entire rear half of the lens, aft of the diaphragm, composed of three different groups. I propose the technical term differential focusing: different parts of the lens moving differently, differentially, during the focusing process.

 

This in the hope of penetration on the level of my "Gnomes of Solms" -- and maybe on better factual grounds.

 

The old man who thinks words are for facts, too

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[giordano]

Lars, I'm always happy to support verbal precision or even pedantry, but it may be too late for a successful claim on differential focusing. "Differential focus" seems to be established as a synonym for "selective focus" or depth of field control.

 

Taxonomically, we seem to have just two main categories plus a few subcategories:

 

1) Lenses focused by moving the entire optical unit relative to the image plane.

a) Optical unit is rigid, all elements move together

One or more elements move relative to the rest of the optical unit during focusing in order to provide best performance over a wider range of magnifications.

2) Lenses focused by changing their focal length. The main optical unit is fixed relative to the image plane, but one or more of the elements move relative to the others.

a) Front-cell focusing (as seen on huge numbers of older 35mm and roll-film cameras and many zoom lenses)

Rear-cell focusing (as on a handful of current lenses)

c) Internal focusing (front and rear cells are fixed but an internal group moves

d) the old 200mm Medical Nikkor that one "focused" by attaching one or other of its set of close-up lenses

e) most "mirror" lenses.

"Floating element" lenses are of course in (1b). "Floating" isn't the best word, partly because these elements have to be very precisely located - but also because there are a few lenses where the group that "moves" relative to the main optical unit is fixed relative to the lens mount (e.g. the original 60/28 AF-D Micro-Nikkor).

 

"Close range correction" is a good term but probably a Nikon trademark. Maybe "compensating focusing"?

[pgk]

"Close range correction" is a good term but probably a Nikon trademark. Maybe "compensating focusing"?

How about "close range optimisation" which is, I assume, what this group is intended to achieve rather than simply correct better at close focus. I cannot remember exactly what phrase Hasselblad used when they introduced designs intended to correct better at close focus, but I think that they too used something like 'close range correction", as did Nikon, with their lenses.

[pop]

...it is no longer even a single group that moves. It is the entire rear half of the lens, aft of the diaphragm, composed of three different groups.

 

If the entire rear half moves in unison, you could call it a "floating assembly" or "subassembly" as opposed to a floating group or element, I suppose.

[NZDavid]

A focus group?

 

Is there a German word for it? A brilliant many-faceted word, like groupmultielementfocussinglens?

[01af]

First came floating elements: One single un-cemented optical element that moved differently from the rest of the optical assembly during focusing. First introduced in the late 1970's, as I remember, to improve extreme close focusing in macro lenses.

The term Floating Elements originally was coined by Canon and quickly became the general term for this feature. Still, other brands weren't originally allowed to use it, so they had to be creative to come up with new names for the same thing (it's the same today with Image Stabilization, or IS—a Canon term again that no-one else can use). Minolta called it Floating Focusing, and Nikon used the term Close-Range Correction, or CRC for short.

 

Today the term Floating Elements seems to be free as many brands, including Leica and Sigma for example, are using it these days—it wasn't always like that.

 

The term Floating Elements never stood for one single un-cemented lens element, as Lars falsely explained—note the trailing letter s which denotes plural. The number of elements which float is, and always has been, unspecified. It may be one, or two, or many. Even in the earliest lenses incorporating floating elements, it used to be two or three elements typically, some possibly cemented, some possibly not. The first lenses with floating elements were fast retro-focus wide-angle lenses in the late '60s and early '70s. The use of floating elements in macro lenses became common only much later. The first Minolta lenses with Floating Focusing were the MC W.Rokkor-NL 21 mm 1:2.8 and the MC W.Rokkor-SI 24 mm 1:2.8 (which also became available as the Elmarit-R 24 mm 1:2.8). By that time, Canon lenses with Floating Elements already were established if I remember correctly. Other brands followed quickly.

 

 

Then came floating groups.

"Floating groups" never was a technical term, and there never was a time of transition from "one single floating element" to "one single floating group of two cemented elements". Lars, you are just making this up in your head.

 

 

Progress marches on. With the Summilux-M 35 mm Asph, new version, it is no longer even a single group that moves. It is the entire rear half of the lens, aft of the diaphragm, composed of three different groups.

While I am not aware of any other lens where the complete rear part of the lens behind the diaphragm moves as a floating focusing group (using the Minolta term to avoid confusion about the number of elements involved), it has been common to move more than one cemented group for decades.

 

 

I propose the technical term differential focusing: different parts of the lens moving differently, differentially, during the focusing process.

No new technical term required, as we already have one. It's called Floating Elements.

 

A real innovation would be two floating sets of elements, moving independently from each other and from the lens' main part. But that would be extremely complex mechanically. As a matter of fact, the complexity has kept regular floating focusing from being incorporated in Leica M lenses (which are supposed to be small) for decades while it was common in SLR lenses already.

 

 

Taxonomically, we seem to have just two main categories plus a few subcategories: [...]

No, it's not that easy. There also are lenses that don't belong into a subcategory of those two main categories but right between them—i. e. lenses that get focused by changing both focal length and image distance. This is typical for modern macro lenses that can focus right down to 1:1 magnification.

 

So we have:

 

• lenses that focus purely by extension (these may or may not incorporate floating elements)
  
• lenses that focus purely by focal length reduction (typical for modern telephoto and many zoom lenses)
  
• lenses that focus by a combination of the two beforementioned principles (typical for modern macro lenses and some zoom lenses)
  

In lenses of the latter type, the weight of the two principles may vary. Short macro lenses (30 - 70 mm) usually focus mainly by extension and only by a small part by focal length reduction. With long macro lenses (150 - 200 mm) usually it's the other way around.

Edited August 11, 2010 by 01af

[01af]

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Is there a German word for it?

In German it's called Nahbereichskorrektur ... which happens to be the literal translation of Nikon's close-range correction.

[pgk]

01af

 

So am I correct in thinking that the original use of floating elements was to produce better image quality as a lens focuses closer? But now floating elements are use in numerous ways which may or may not produce better close focus image quality? And is the purpose of the floating elements in the new Sumnmilux simply to adjust focus and maintain high quality image quality or does it also reduce focus shift, or is focus shift simply reduced by the overall new design?

[01af]

So am I correct in thinking that the original use of floating elements was to produce better image quality as a lens focuses closer?

Yes, exactly.

 

 

But now floating elements are use in numerous ways which may or may not produce better close focus image quality?

No. It still is intended to improve the lens performance when focused at short distance.

 

 

And is the purpose of the floating elements in the new Sumnmilux simply to adjust focus ...?

No. Focus is adjusted by rotating the focus ring.

 

 

... and maintain high quality image quality ...?

Yes.

 

 

... or does it also reduce focus shift, or is focus shift simply reduced by the overall new design?

Focus shift is caused by spherical aberration, so it is reduced by spherical aberration reduction. The aspherical element helps a lot, and floating elements also indirectly help by improving the general lens aberration correction at distances shorter than infinity.

Edited August 11, 2010 by 01af

[giordano]

So am I correct in thinking that the original use of floating elements was to produce better image quality as a lens focuses closer?

 

Yes. This Nikon | Imaging Products | NIKKOR - The Thousand and One Nights, Tale 14 : NIKKOR-N Auto 24 mm f/2.8 explains the thinking behind the first (I think) use of them. Note that the "floating" part in that first lens consisted of three elements in two groups.

 

But now floating elements are use in numerous ways which may or may not produce better close focus image quality?

"Floating elements" in the sense that started this thread are mostly about maintaining image quality at shorter distances.

 

And is the purpose of the floating elements in the new Sumnmilux simply to adjust focus and maintain high quality image quality or does it also reduce focus shift, or is focus shift simply reduced by the overall new design?

Floating elements by themselves cannot reduce focus shift (unless they're connected to the aperture ring as well as the focus ring). But by reducing the impact of focus distance on performance, they give the designers more freedom in other areas - which could include minimising focus shift.

[wildlightphoto]

This Nikon | Imaging Products | NIKKOR - The Thousand and One Nights, Tale 14 : NIKKOR-N Auto 24 mm f/2.8 explains the thinking behind the first (I think) use of them.

 

IIRC the 24mm f/2.8 Nikkor was the first lens that used floating elements, in the late 1960s.

[Xmas]

"Floating elements" in the sense that started this thread are mostly about maintaining image quality at shorter distances.

Hi

 

Alas don't think this is a new technique, seen a photo of an Victorian lens with a 'set the arrows together for optimum definition' I presumed this was only for one distance setting.

 

RB67 lenses moved separate groups of elements in early 70s, for optimum close focus, for their wide angles, the macro only moved a cementer doublet.

 

For Lars - Mamiya called it a 'floating system' & they indicated it was for off axis sharpness close up...

 

There is a cost in complexity as another precision helicoid is needed.

 

I'm so used to my pre asph foibles I'm not tempted, by the aspherical, or either of the asphs, on size and weight alone, don't see why they did not stay within the same dimensions. I carry the lens all day only shoot a few 1/125 of a seconds.

 

Noel

[giordano]

I carry the lens all day only shoot a few 1/125 of a seconds.

 

:D

[Xmas]

:D

Hi

 

Schlepping a gbag all day in cold or heat is difficult, if I know I don't need f/1.4 I substitute a CV f2.5 35mm from the LTM gbag, lighter still and more ergonomic, mine is not detectably different at f/5.6, in the corners from the lux.

 

Noel