Archived posting to the Leica Users Group, 2004/11/03
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]I wouldn't go so far as to say that APO is a term projecting absolute quality. It's more in the line of a relative value. It's my understanding that apo lenses focus all the color sources at a specific focus distance set by the manufacturer. The other ranges, more or less, work like any other optic. I'll gladly stand corrected if I'm wrong. S. Dimitrov > From: Frank Dernie <Frank.Dernie@btinternet.com> > Reply-To: Leica Users Group <lug@leica-users.org> > Date: Thu, 4 Nov 2004 06:30:16 +0000 > To: Leica Users Group <lug@leica-users.org> > Subject: Re: [Leica] LHSA convention cluster bombs Part One The Beginning. > > Hi William, > I do think it is fair to say that APO tells you how sharp a lens is and > is an absolute statement of quality. It does not give a clue as to > whether you will like the boke. You need the actual MTF curves to > evaluate the boke (My limited experience convinces me that the > explanation in the "Lens Work" book is the first I have seen to be > right in every case on boke). > Asph on the other hand tells you nothing. Most lenses made today are > "asph" including many spectacles and pretty well all P&S and digicam > lenses. Leica use asph lenses for the same reason as others, to get the > quality at a lower price due to fewer lens elements. When asph elements > were hand ground they were extremely expensive. Ground asph lenses > still are very expensive but hot pressed ones, as used by Leica and > others, are no longer prohibitive. > Frank > > On 4 Nov, 2004, at 03:12, William G. Lamb, III wrote: > >> >> Dan, >> >> Sorry, twelve-hour day in the office today and am just getting to my >> mail... >> >> "Bokeh" is one thing, "brittleness" is another. I'm not saying that APO >> correction generally means that some images in harsh side-light will >> be brittle. I'm observing that LEICA lenses in the 90mm - 100mm range >> appear to have this tendency, whatever their reasons may be, the 90 APO >> ASPH in particular. >> >> Since 2000, the direction Leica has been going in lens design as >> exhibited >> by the 28 ASPH is a GOOD THING in my view. The results aren't harsh >> and the corrections produce images in contrasty light which would have >> been almost impossible a few years prior. As I said earlier, I have >> ordered >> a 50 ASPH in the hope that this trend in lens design continues. I'm >> just >> suspicious of the APO correction Leica did in the past and won't buy a >> lens on blind faith with this designation until I've seen many >> examples of >> its output. Trust this clarifies... >> >> William >> >> At 08:06 AM 11/03/2004 -0500, you wrote: >>> I've missed something here. I can understand why someone might not >>> like >>> the ASPH correction in a lens; I *think* it is residual spherical >>> aberation which is the basis for lovely "bokeh" which people get soft >>> and >>> fuzzy over (or conversely might be the cause of "brittleness"), and >>> which >>> is highly corrected in aspherical designs. APO design merely >>> reduces >>> chromatic aberation, which I can't see having an unintended >>> detrimental >>> effect on a len's performance. >>> >>> -dan c. >>> >>> At 07:48 AM 03-11-04 -0500, William G. Lamb, III wrote: >>>> >>> [snip] >>>> >>>> So let's not get too wound up here, O.K.? I would LOVE to fill that >>> 75mm >>>> frame on two of my M's. If it's an ASPH, that could be very good. If >>> it's >>>> got APO correction, I'll be more inclined to wait and see some >>> results >>>> before springing for one. That's all... >> >> >> _______________________________________________ >> Leica Users Group. >> See http://leica-users.org/mailman/listinfo/lug for more information >> > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information