Could anyone tell me the meaning and main features of ASPH for leica lens.

-- KL (klrltl@yahoo.com), September 18, 2001

Answers

ASPH is short for aspherical. In Leica's case ASPH denotes the use of one aspheric surface on a lens element. There's one Leica M lens with two aspherical elements: Summilux-M 1.4/35mm Aspherical of which only 2000 were made. Aspherical lens elements allow lens designers to make optical corrections impossible to achieve in traditional lens designs.

-- Bert Keuken (bkkn@casema.net), September 18, 2001.

Just to save a little time and space, here is a note I saved earlier:
"M ASPH -- To be or not to be"
(http://www.greenspun.com/bboard/q-and-a-fetch-msg.tcl?ms g_id=005LjN)

I personally, today, upon purchase of any current lens would almost always buy the ASPH version, just because that is the most modern -- altho most expensive. The current 21, 24, 28, 35s, and 2/90 are all ASPHs. One exception: I myself would not buy the 2/90, but the 2.8/90 instead, but that's another story.

Hope that helps. Mike

-- Michael Kastner (kastner@zedat.fu-berlin.de), September 18, 2001.

Arghhhh... "M ASPH -- To be or not to be":

http://www.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_id=005L jN

-- Michael Kastner (kastner@zedat.fu-berlin.de), September 18, 2001.

One properly designed aspherical element can generally replace two (and sometimes three) conventional elements in a lens design. Fewer elements translate into better transmission and less opportunity for spherical and chromatic abberation. Better transmission generally means better contrast, and lower levels of abberations generally mean better resolution. Adding APO (APO-chromatic), ED (Extra low dispersion), L (Low dispersion) or FL (FLourite) glass to the above equation further reduces chromatic abberations. However, the key phrase in this equation is "properly designed"...

-- Jack Flesher (jbflesher@msn.com), September 18, 2001.

ASPH lenses will tend to minimize distortions and aberrations while increasing sharpness and contrast at both near and far distances, this according to an 'optical expert' friend of mine. I have the Leica 21mm/f2.8 ASPH and 35mm/f2 ASPH lenses, and the performance of both lenses is stunning!.....................

-- Muhammad Chishty (applemac97@aol.com), September 18, 2001.

There is a history with Leica and aspheric lenses. 1. Leica introduced what (I believe, correct me if this is wrong) was the first regular production aspheric lens, in 1966: The 50/1.2 6-element Noctilux. It contained two hand ground and polished aspherical surfaces. The lens was diffeicult to produce and was made only in tiny numbers (mostly between '66 and '68). The 50/1.2 was replaced by the 7-element 50/1.0 Noctilux with no aspherical surfaces. Oddly, the original 50/1.2 Noctilux was not widely advertised as having aspherical surfaces.

2. The first version of the 35/1.4 Summilux Aspherical (#11873) of ca. 1990 also had two hand ground and polished aspherical elements - very hard to make. Leica gave up on this design after producing some 1000 or fewer lenses, with very long production delays.

3. The term ASPH was first used to designate the lens that replaced the 35/1.4 Aspherical model, now designated 35/1.4 ASPH (#11874), perhaps to distinguish it from the earlier model. The 35/1.4 ASPH lens has a single aspherical surface, but this time produced by glass molding, using a process obtained by agreement with Canon.

4. The more recent series of ASPH lenses utilize glass molding, a precision technique involving a computer controlled (CNC) lathe, or another recent modification to generate aspherical surfaces to the required tolerances. The larger the aspherical surface (eg, as in the Apo-90/2.0-ASPH) the harder it is to make with the required precision.

The Leica ASPH lenses are optically excellent not simply because of the aspherical elements (many point and shoot leneses have two or more aspherical surfaces), but because of the overall design and production methods. Many of these lenses also feature elements with highly refractive glasses, and elements with partial anomalous dispersion, to correct for various aberrations besides spgherical aberration.

-- Eliot (erosen@lij.edu), September 18, 2001.

According to the Leica management, the 2000 ex. promised of the first version of the 35/1.4 Summilux Aspherical (#11873) were made.

Lucien

-- Lucien (lucien_vd@yahoo.fr), September 19, 2001.

Lucien. According to Jim Lager, the initial number of 2000 35/1.4- Summilux Aspherical 11873 leneses that were scehduled to be produced was later revised to 1000. However, it is not known if they even completed the 1000. There were continued problems during the production of this lens. First, it was very difficult and time consuming to hand grind and polish two Aspherical surfaces to the required precision. Apparently, there was only one technician at the factory that could do this reproducibly, and even so, the rejection rate was very high. Secondly, Leica apparently lost the barrels for these lenses during the move from Canada to Germany, and had to wait for production of new barrels (I think the barrels were made in Japan by Sigma).

It is also unlikely that more than 1000 of these lenses were made, just juding by the infrequency with which they appear in dealers' stocks and on eBay. In any event, this is a very rare lens.

-- Eliot M. Rosen (erosen@lij.edu), September 19, 2001.

In Leica parlance ASPH seems to mean particularly good performance and APO means best performance. APO usually only applies to tele lenses. Some lenses are APO-ASPH. I hesitate to say it is a marketing gimmick, but there are elements of this in this new obsession. As someone else mentioned - no big deal was made of the original Noctilux when it had aspherical lenses - now all good things have to have aspherical/apo/ED/L etc. mumbo jumbo (all of Sigma's lenses seem to be "Apo"!)

Still suffice it to say - the Leica ASPH have an aspherical element and the term indicates that you are getting the latest and greatest Leica design of the focal length in question. The trouble with all this stuff is what will Leica do when they design something after the 35 ASPH? What designation will they have to dream up?

-- Robin Smith (smith_robin@hotmail.com), September 20, 2001.

Follow-on to Robin Smith: Supposedly the very last Nikon AI 180 lenses had ED glass in them, but nobody thought to put ED in the name until the AIS version came out (1983). I think it's called blowing your own horn.

The meaning of ASPH: To focus parallel wavefronts of light or sound or water to a single point you need an elliptical or parabolic reflector or refraction device. It is very expensive and tricky to make accurate parabolas or ellipses - but back in the time of Galileo, Leeuwenhoeck et al it was discovered that spherical glass surfaces are relatively easy to make and, when they are just slightly curved, form a reasonable APPROXIMATION of a parabolic surface. So almost all lenses have been made that way. Most of the complex multi-element photographic lens designs of the past 100 years have been attempts to correct the SPHERICAL and other aberrations that come from "faking" a parabolic focus using spherical surfaces.

Starting around 1980 consumer optical designers and manufacturers, having pretty much reached the limits of what they could do with spherical surfaces, began looking for techniques other than traditional spherical grinding that would make ASPH surfaces cost- effective. Leica's aspherical molding technique is one of the successful outcomes.

Among other things ASPH lens surfaces allow the lens designer to make better corrections of various aberrations, producing mopre sharpness over more of the image area; OR they allow the designer to use fewer elements while retaining sharpness, and fewer elements mean fewer reflections, which leads to MORE contrast.

Don't confuse ASPH and APO. APO has to do with eliminating chromatic aberrations and is done using the REFRACTIVE INDEX of the glass and NOT its shape, per se. Glass, like raindrops, and as seen with triangular prisms, tends to break light up into separate colors, which focus at slightly different points (fuzziness) and form images of slightly different sizes (color fringing). Chromatic aberrations are most visible in long-focus lenses, because they are magnified with the rest of the image. APOchromatic correction uses a mixture of glasses with different refractive indexes (especially Extra-low Dispersion "ED" glass) to recombine the different wavelengths of light to form a single sharp image with less fringing. (APO corrects red, green AND blue - Achromatic corrects 2 of the three colors - just think: almost ALL of your lenses could be labeled ACHR.)

You will not likely see an APO wide-angle lens because wide-angles usually don't have much trouble with chromatic aberration. You WILL see both ASPH wideangles and ASPH telephotos since ASPH lens shapes have features useful for any kind of optical design, even the little plastic dealies that sit in front of meter cells to focus the light (see M6, Hexar RF, G2)

-- Andy Piper (apidens@denver.infi.net), September 21, 2001.