Re: Big richfield refractor

From: Mike Jones (jonesmi_at_airmail.net)
Date: 11/07/04 

Date: Sun, 07 Nov 2004 16:49:10 -0600

RichA wrote:
>
> On Sun, 07 Nov 2004 14:18:33 -0600, Mike Jones <jonesmi@airmail.net>
> wrote:
>
> >"Richard F.L.R. Snashall" wrote:
> >>
> >> Mike Jones wrote:
> >>
> >> >Dan Chaffee wrote:
> >> >
> >> >
> >> >
> >> >>
> >> >>
> >> > 5 8.760 0.600 S-FSL5 3.1
> >> > 6 -10.039 0.218 3.1
> >> > 7 -10.446 0.500 SF1 2.8
> >> > 8 -31.994 4.625 3.1
> >> > IMG Infinite 1.4
> >> >
> >> >
> >> Is there any particular reason you went with S-FSL5 instead of
> >> (more known to this group and oft maligned herein;-) N-FK5?
> >>
> >> >
> >> >
> >>
> >> --
> >>
> >> Rick S.
> >>
> >> http://users.rcn.com/rflrs
> >
> >I don't care, whichever's cheaper. Isn't Ohara's S-FSL5 a great deal
> >cheaper than Schott's N-FK5? A Schott field rep told me once that Ohara
> >can sell ED-type glasses more cheaply than them because Canon buys so
> >much ED glass from Ohara.
> >Mike
>
> I wish they'd work on new glasses. One of the latest
> Canon lenses has 15 elements, 3 of which are ED and
> they still have horrible chromatic aberration unless
> you stop them down quite a bit.

You ain't the only one. We all need a bigger selection of abnormal
dispersion glasses with good optical, physical and chemical
characteristics that cost less than pure Europium. We need glasses like
880850 and 485230, out in the empty corners of the glass map. We need
to get even farther away from the dPgF, dPFe, etc. normal lines.
Seven-color crossing lenses over the 0.37-1.01µm band or even wider
would be possible, with resulting performance indistinguishable from
unobstructed mirrors but with much wider well-corrected fields. I know
of special short-run proprietary blends of abnormal dispersion optical
glass and liquids being made at certain companies for specific jobs, but
they are internally funded and held tightly to the chest. Optical
liquids have very unusual dispersion properties, but have inhomogeneity
problems in thermal gradients due to higher dn/dT. So, in the
non-proprietary world, you just do the best you can by including as many
glass catalogs as you can, from Schott, Ohara, Hoya, Sumita, etc.
Mike

Relevant Pages

  • Re: Megrez 80 Triplet?
    ... > explaining why Megrez used now ED glasses. ... > What are you calling SD and what are you calling ED glass? ... > dispersion numbers above 80 and partial dispersion far from Abbe line are ... The marketing world for birding optics tends to confuse things even more. ...
    (sci.astro.amateur)
  • Re: Megrez 80 Triplet?
    ... SD glasses are easier to wrk than ED but there is maybe a hidden reason ... What are you calling SD and what are you calling ED glass? ... dispersion numbers above 80 and partial dispersion far from Abbe line are ED ... to me is a marketing term. ...
    (sci.astro.amateur)
  • Re: Megrez 80 Triplet?
    ... > explaining why Megrez used now ED glasses. ... > What are you calling SD and what are you calling ED glass? ... > dispersion numbers above 80 and partial dispersion far from Abbe line are ED ...
    (sci.astro.amateur)
  • Re: broken china
    ... Wine glasses have a short live expectancy in this ... Her husband gave me a nice crystal wine glass. ... except for the space three ice cubes occupy, that's his drink... ...
    (rec.food.cooking)
  • Re: ping hans re bourbon
    ... every major problem could be solved just with potatoes, ... That must be one hell of a bourbon! ... Enjoy the Woodford,preferably from a glass like this ... As far as I know these type of glasses are also called Renault glasses. ...
    (alt.2600)