[rollei_list] Re: WTB: SL66 thingies
- From: Jerry Lehrer <jerryleh@xxxxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Wed, 24 May 2006 13:22:10 -0700
Richard,
The Patek Phillipe is almost finished, thank you!
Jerry
Richard Knoppow wrote:
> ----- Original Message -----
> From: "Eric Goldstein" <egoldste@xxxxxxxxx>
> To: <rollei_list@xxxxxxxxxxxxx>
> Sent: Tuesday, May 23, 2006 2:54 PM
> Subject: [rollei_list] Re: WTB: SL66 thingies
>
> > Perhaps there is... Kingslake does not classify the
> > 5-element Gauss
> > lenses as symmetrical nor even semi-symmetrical. In fact,
> > he is so
> > strict about his classification of symmertical lenses that
> > even the
> > Opic-types do not qualify... they are classified as
> > "unsymmetrical
> > double-gausses"
> >
> >
> > Eric Goldstein
> >
> That is Kingslake's classification, he is being very
> rigorous. In his book on lens history he definitely
> separates perfectly symmetrical lenses from those having
> similar construction but different powers in each half. For
> instance, he calles the original Planar a symmetrical lens
> but the Opic a non-symmetrical one. The curious thing is
> that he includes the Schneider Angulon in his discussion of
> symmetrical lenses even though it has a similar shift of
> power from one side to the other.
> I think this overlooks the way symmetry works in a lens.
> The idea is that the three lateral aberrations in each half
> have similar values but opposite signs and will cancel, at
> least to some degree. In a completely unsymmetrical lens,
> like the Tessar, this doesn't happen because the two sides
> of the stop have completely different properties. The front
> (as normally made) has an overall negative power and the
> back positive power. In fact, the Tessar uses the front
> section to correct the aberrations of the back, the front,
> of course, being a negative lens, will not form an image.
> The back will form a highly aberrated image.
> Lenses of the symmetrical or partially symmetrical type
> have aberrations and powers distributed in both halves and
> both halves will form images by themselves.
> The 5 element Planar or Xenotar looks at first sight as
> though it has no symmetry. In fact, it has quite a lot. The
> approach to this design was to eliminate one element of a
> Planar type by combining the powers of two of the elements
> into one. In the Planar, and its decendants, the cemented
> surfaces in the negative elements are used to correct
> chromatic aberration. Where a wider choice of glass is
> available its possible to correct the chromatic by means of
> the positive and negative elements in the half lens. So, in
> the Xenar one has a front positive element, a negative
> component composed of two cemented elements, and, in back of
> the stop, a negative element consisting of a single lens,
> and a positive element consisting of a single lens. The
> arrangement in the 5 element Planar is a little different
> because it is the front component that has the cemented
> surface, but the overall arrangement is the same i.e., four
> components arranged as +,-, stop, -, +. Again, both halves
> are positive in overall power and will form real images. The
> distribution of power and aberrations is such as to obtain a
> significant amount of cancellation of the lateral
> aberrations. This cancellation is one reason this type
> performs better at large apertures than the Tessar. In
> addition, the Planar either five or six element, has much
> less oblique spherical aberration that the Tessar. Since
> this aberration, like coma, is dependant on image height, as
> well as the aperture, having some means of correcting it
> allows the use of larger apertures and and allows a larger
> image field for a given aperture.
> The three Wynne patents Kingslake cites for the 5 element
> lens are worth reading.
> USP 2,499,264 2,487,749 2.487,750
> Also, see if you can find one of Kingslake's books on lens
> design, he wrote a couple and goes into this more
> completely. Another good book on lens design that is
> reasonably understandable is _Modern Lens Design_ Warren J.
> Smith. This has run to a second edition. If you are rich get
> the second, otherwise the first edition is just fine. Smith
> was one of the developers of the lens design program now
> known as Oslo, and, like Kingslake, is a particularly lucid
> writer.
>
> ---
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk@xxxxxxxxxxxxx
>
> ---
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