[rollei_list] Re: 500/5.6 Tele Tessar for SL66 Comments
- From: Carlos Manuel Freaza <cmfreaza@xxxxxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Fri, 5 Jan 2007 23:30:43 -0300 (ART)
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
> > >
> > >
> > >
> > >
> > >
> > >
> > > ---
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