Digital Combo: Leica M240 + Summilux 35 FLE

[Jeff S]

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FWIW, in every written or video interview I've seen with Peter Karbe, he states that the purpose of the floating element is to better optimize focusing at close distances...simple as that. How this occurs is another, more complicated, story.

 

See, for instance, this discussion of the 50 Summilux asph (and the older 35 Summilux). Down the page, he says...

 

"PK: One foible of all high aperture lenses is the fact that these lenses can be optimized for one distance only (infinity). To maintain the optical performance at close focusing distances an additional degree of freedom is needed. This was realized by employing a floating element for the design of the Summilux 50mm f/1.4 ASPH."

 

It's also interesting to read about the challenges of introducing a floating element; it's typically not nearly as simple as inserting one in an existing design.

 

Jeff

[Peter Branch]

It was certainly stated by various authors, including I believe E. Puts, that the 35mm S'lux FLE had an "identical" optical formulation to the previous version but the incorporation of a "Floating Element", (actually a Cell), allowed for a number of abberations, including focus shift, to be reduced.

 

I've always been suspicious of this statement because presumably the separation of the two Cells in the original version was set at some compromise value and at some focusing distance the Cells in the FLE version will have exactly the same separation as in the original. Hence the performance will, at that focusing distance, be exactly the same.

 

This seems to me to be a key point which needs to be resolved before any meaningful discussion can take place.

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[01af]

... Peter Karbe, he states that the purpose of the floating element is to better optimize focusing at close distances ... simple as that.

Uh oh. Before reporting what Peter Karbe (or anyone) stated, you (or anyone else) should understand the statements in the first place.

 

 

Down the page, he says ...

 

"PK: One foible of all high-aperture lenses is the fact that these lenses can be optimized for one distance only (infinity). To maintain the optical performance at close focusing distances, an additional degree of freedom is needed. This was realized by employing a floating element for the design of the Summilux-M 50 mm 1:1.4 Asph."

There you have it—where is he talking about "optimise focusing"? Nowhere. Instead he is talking about "maintain optical performance" ... as in, avoiding the performance fall-off at close focusing distance. Not a single word here about aperture-related focus shift. So—please don't interpret things into other persons' statements that aren't here.

 

 

It's also interesting to read about the challenges of introducing a floating element; it's typically not nearly as simple as inserting one in an existing design.

That's what I keep saying.

[Jeff S]

If you weren't so combative, you'd realize that I quoted this as FYI, while recognizing that what he says is entirely consistent with your view.

 

You're parsing words on my perhaps awkward phrasing about optimizing close focus; clearly this was only a lead-in to his exact phrasing about optimizing performance at close focus distances. Doesn't take a rocket scientist to understand that apertures weren't mentioned, which was precisely my intent. My concluding sentence was also obviously made in light of your comments.

 

Jeff

Edited February 18, 2013 by Jeff S

[01af]

If you weren't so combative, you'd realize that I quoted this as FYI, while recognizing that what he says is entirely consistent with your view.

 

You're parsing words on my perhaps awkward phrasing ...

Oops. Sorry! I guess I owe you one

 

I'm so used to people re-iterating all these misconceptions about floating elements in general and the Summilux-M 35 mm Asph (FLE) in particular over and over, as well as mis-quoting the experts ... so I indeed over-interpreted your "optimize focusing at close distances" wording, thus making the same mistake I was blaming you for. My apology.

[Jeff S]

No problem.

 

I recall one Karbe interview (can't locate it right now) where he explains the rationale for the floating element to some Leica users (I think it was to some invited guests during one of the product introductions), and they were surprised when he boiled it down to the simple aspect of optimizing close focus performance (you know what I mean). The audience seemed puzzled and tried to complicate matters, but to their surprise, he dismissed other intentions and just reiterated his point. He did, however, remark that it was easier said than executed.

 

Jeff

Edited February 18, 2013 by Jeff S