Archived posting to the Leica Users Group, 1999/01/25
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Bill,
Thanks for the quotes.
Erwin,
Thanks for the precisions
For what it's worth, I've gone though a little reference scouting
myself...
The following link seems interesting from what looks like a lower end
glass manufacturer's perspective (in 'Czech English'):
http://www.ecoglass.cz/techno.htm and
http://www.ecoglass.cz/index_e.htm#Aspheric Lens Production
And this from Canon:
QUOTE
"Depending on the purpose, Canon now uses 4 different aspherical lenses
in its products:
(1) a ground aspherical lens;
(2) a glass-mold aspherical lens;
(3) a high-precision, plastic-mold aspherical lens; and
(4) an ultraviolet cure resin-coated replica lens.
Among them, the wide-bore, ground aspherical lens is employed in the L
lens series for performance improvement. "
UNQUOTE
(1) seems equivalent to the technology used for the 1st 35mm f1.4
aspherical
(2) seems equivalent to the current Leica data sheets.
My question: is the reason for maintaining production of very expensive
ground aspherical lenses due to the size of the glass elements involved
? Would that explain why there is no R aspherical lens up to now ?
On another level, reading the original German version of the text for
the 35mm f2 Asph, I see no mention of 'glass':
QUOTE
"Zum Erreichen dieser außergewöhnlichen Objektivleistung bei zugleich
kompakter Bauweise war der Einsatz einer asphärischen Fläche
unumgänglich. Wie schon im SUMMILUX-M1:1,4/35 mm ASPH. und dem ELMARIT-M
1: 2,8/24 mm ASPH. wird diese von der Kugelform abweichende Fläche
mittels eines modernen „Präzisions-Blankpress-Verfahrens” erzeugt. Dazu
wird ein diamantgedrehtes und poliertes Werkzeug aus einem
keramikartigen Material eingesetzt. Der so entstandene „Prägestempel”
entspricht in umgekehrter Form exakt der endgültigen Oberfläche der
damit zu fertigenden Linse."
UNQUOTE
The text mentions "Fläche", which I translate by "surface". Funny
enough, it does not mention the material used to create that aspherical
surface, though it mentions at length the material used for the mould
itself ("keramikatrigen Material").
A lot of companies avoid using the term 'plastic' or 'resin' and use
'organic glass' instead, or remain silent on the subject. I wonder...if
it really matters at all ?!
Alan
WILLIAM CALDWELL wrote:
>
> SNIP --
>
> Jim Brick wrote:
> > I just read in the M6 version of Leica Fotografie International, about the
> > 12 ASPH, "one element with an aspheric GLASS surface". So we know at least
> > one surface is glass! The discussion about the 24 ASPH implies a glass ASPH.
>
> SNIP --
>
> Jim and Dick,
>
> The "Leica Product Information Sheet for the f/2.8 21mm ASPH Elmarit-M
> (IX/97/HX/B)" also indicates that the aspherical element for that lense
> is glass. At page 2 of this Product Information Sheet, it is stated:
>
> "Like the other new wide-angle lenses for the LEICA M system, i.e.,
> the SUMMILUX-M f/1.4/35 mm ASPH., the ELMARIT-M f/2.8/24 mm ASPH., ...
> the aspherical glass surface is produced by high-precision 'blank
> moulding'. A diamond-turned, accurately polished die manufactured from
> a type of ceramic is employed for this process. The die manufactured in
> this way corresponds perfectly in reverse to the surface of the lens to
> be manufactured." (Caps appear in original quote.)
>
> The authors of the article in "Viewfinder" Vol. 30, No. 1, "The 35mm
> f/1.4 Aspherical Summilux vs. The ASPH - Which is Better," are both
> highly knowledgeable Leicaphiles. The article states in part: "Ed
> Schwartzreich owns the earlier "Aspherical" model with the two
> aspherically ground glass element surfaces, and Dick Gilcreast owns the
> later "ASPH" model with the single aspheric surface of pressed plastic
> bonded onto one of the glass elements."
>
> Perhaps the difference is that the Aspherical f/1.4 contains two ground
> aspherically glass elements (among its other elements) and the ASPH
> f/1.4 contains only a single molded or pressed aspherical glass element
> (hence the use of the word, "plastic") among its elements. This latter
> comment on the meaning of a word used by someone else in a journal is
> sheer speculation on my part, and someone with more resources and
> knowledge of the two lense versions will have to contribute on this
> point. It should be noted that diagrams of the elements of the ASPH
> f/1.4 show the aspherical element in the interior of the lens element
> groupings and not as a front or rear element.
>
> Dick, I do not subscribe to, or have present access to the Leica
> Fotografie, 6/97 and 7/97 and the two articles you to which you refer,
> "Aspherics - The Optician's Magic Word," and "Aspheric Technologies" (in
> which the approach of Leica and its methods of fabricating these
> elements is set forth). Thanks for the references though, I will try to
> obtain copies of the articles.
>
> Best regards and the best of light today,
>
> Bill Caldwell