I had found Bob Salomon's definition on the basis of that obscure DIN standard (according I understood then, he discussed with Richard about the topic): > According Bob Salomon, a more precise definition > about > an APO lens is that the lateral chromatic > aberrations > of the secondary spectrum are reduced to within a > minute percentage of the focal length of the lens. I > add about lateral chromatic aberrations of the > secondary spectrum that "Lateral", as in lateral > colour, means at right angles to the optical axis in > the plane of focus. It fundamentally indicates a > difference in image size for different wavelengths > of > light. Secondary spectrum includes all colours not > brought to a common focus,in other words Salomon > says > the lateral chromatic aberrations of the secondary > spectrum are corrected to within a percentage of the > focal length of the lens, he said that the > definition > is according a D.I.N. definition. And this an optical technician opinion: http://geogdata.csun.edu/~voltaire/tmb/definition.html All the best Carlos --- Eric Goldstein <egoldste@xxxxxxxxx> escribió: > Richard and I had a similar discussion about a Kino > 100/2 APO lens on > another list and contacted the manufacturer for the > performance > specs/curves. Sure enough, the lens was not close to > APO as defined by > the traditional definition of convergence on 3 > points of the visible > spectrum. > > There is apparently a DIN standard which is so > poorly defined as to > allow most any lens to be labeled APO. > > Eric Goldstein > > -- > > On 1/5/07, Ellestad <ellestad@xxxxxxxxxxx> wrote: > > Thanks for an overdue discussion on this, Richard! > > > > I have wondered about this very thing for years. I > fellow that I know who is > > likely "in the know" told me that while he > couldn't give me the technical > > requirements for true APO status he did know that > sales and marketing had > > gotten pretty casual with the term. > > > > This might explain why we were often underwhelmed > with the performance > > improvements of these "APOs". > > > > Tim > > > > ----- Original Message ----- > > From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx> > > To: <rollei_list@xxxxxxxxxxxxx> > > Sent: Friday, January 05, 2007 6:11 PM > > Subject: [rollei_list] Re: 500/5.6 Tele Tessar for > SL66 Comments > > > > > > > > > > > > > > > > I wonder if the lens is truly apochromatic. > A lot of > > > current lenses with the name prefix APO are just > well > > > corrected achromats. A true apochromatic lens is > corrected > > > for longitudinal chromatic aberration for three > colors and > > > spherical aberration for two colors. In > addition, most are > > > corrected for lateral chromatic aberration. The > published > > > data for the current crop of "APO" lenses often > includes a > > > graph of longitudinal chromatic deviation, i.e., > the change > > > in focus for color. These cross the zero line > twice, an > > > apochromat will cross the center line three > times. > > > Note that the overall chromatic deviation > of an > > > apochromat is not necessarily better than an > achromat. The > > > apochromat may be correct for three colors but > still have > > > greater deviation outside of these colors. This > is probably > > > rare in a commercial true apochromat but still > quite > > > possible. An apochromat is not necessarily a > better > > > performing lens than a acromat. The overall > performance > > > depends on many other factors beside > longitudinal color > > > correction. > > > I will add that many telephoto lenses, > especially some > > > of the early ones had severe color fringing. > This may have > > > been due to poor longitudinal chromatic > correction but the > > > extreme asymmetry of such lenses can lead to > large amounts > > > of lateral chromatic. This aberration is one > where the > > > _focus_ of the colors is not too different but > the _size_ of > > > the image varies. A completely symmetrical lens > operating at > > > equal image and object distances (completely > symmetrical > > > optical path) is inherently free of lateral > color, however, > > > symmetrical lenses, even for objects at > infinity, have > > > substantial cancellation of lateral color. > Non-symmetrical > > > lenses, like the Tessar or any telephoto or > retrofocus lens, > > > must be corrected for lateral color in other > ways than > > > relying on symmetry or partial symmetry. > > > > > > --- > > > Richard Knoppow > > > Los Angeles, CA, USA > > > dickburk@xxxxxxxxxxxxx > > > > > > > > > > > > > > > > > > > > > --- > > > Rollei List > > > > > > - Post to rollei_list@xxxxxxxxxxxxx > > > > > > - Subscribe at rollei_list-request@xxxxxxxxxxxxx > with 'subscribe' > > > in the subject field OR by logging into > www.freelists.org > > > > > > - Unsubscribe at > rollei_list-request@xxxxxxxxxxxxx with > > > 'unsubscribe' in the subject field OR by logging > into www.freelists.org > > > > > > - Online, searchable archives are available at > > > //www.freelists.org/archives/rollei_list > > > > > > > --- > > Rollei List > > > > - Post to rollei_list@xxxxxxxxxxxxx > > > > - Subscribe at rollei_list-request@xxxxxxxxxxxxx > with 'subscribe' > > in the subject field OR by logging into > www.freelists.org > > > > - Unsubscribe at rollei_list-request@xxxxxxxxxxxxx > with > > 'unsubscribe' in the subject field OR by logging > into www.freelists.org > > > > - Online, searchable archives are available at > > //www.freelists.org/archives/rollei_list > > > > > --- > Rollei List > > - Post to rollei_list@xxxxxxxxxxxxx > > - Subscribe at rollei_list-request@xxxxxxxxxxxxx > with 'subscribe' > in the subject field OR by logging into > www.freelists.org > > - Unsubscribe at rollei_list-request@xxxxxxxxxxxxx > with > 'unsubscribe' in the subject field OR by logging > into www.freelists.org > > - Online, searchable archives are available at > //www.freelists.org/archives/rollei_list > > __________________________________________________ Correo Yahoo! Espacio para todos tus mensajes, antivirus y antispam ¡gratis! ¡Abrí tu cuenta ya! - http://correo.yahoo.com.ar --- Rollei List - Post to rollei_list@xxxxxxxxxxxxx - Subscribe at rollei_list-request@xxxxxxxxxxxxx with 'subscribe' in the subject field OR by logging into www.freelists.org - Unsubscribe at rollei_list-request@xxxxxxxxxxxxx with 'unsubscribe' in the subject field OR by logging into www.freelists.org - Online, searchable archives are available at //www.freelists.org/archives/rollei_list