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Re: [William-Optics] Re: What's the "SD" stand for?

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  • yahoogroups
    The astrosurf article creates as many questions as it answers. I suspect English is not the authors first language. [No offense intended.] At one point SD is
    Message 1 of 34 , Oct 5, 2005
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      The astrosurf article creates as many questions as it answers. I suspect
      English is not the authors first language. [No offense intended.] At
      one point SD is dismissed as a marketing ploy, then later SD is
      considered to be the ultimate.

      My gut feeling is unless it says fluorite, it won't really be APO. This
      does leave the question as to whether a triplet ED is better than a
      doublet using fluorite.

      And what do you make of this statement?:
      An uncoated Fluorite is sensitive to moisture and this is for this
      reason that some manufacturers offer a 30-year warranty on their lenses.

      What would really help is a simple ranking of UD, ED, SD, fluorite, etc

      Timm Bottoni wrote:
      > Hi Tim,
      >
      > I have the Megrez II SD package, bought it in August and so far am
      > very happy with it for the price. I'm honestly not sure what the SD
      > stands for in this case, but while researching lenses I found this
      > link
      > http://www.astrosurf.org/lombry/reports-coating2.htm
      >
      > I also wrote this review on Astromart
      > http://www.astromart.com/articles/article.asp?article_id=297
      >
      > Again, I am very happy with the quality of it, but if I had the
      > money, I would probably have moved up to the ED triplet. It was just
      > out of the range of my budget for not. I hope to upgrade to it some
      > day. There is no question that the "Semi-APO" still has false
      > color, and from what I have read the true 3 element APO has
      > virtually none. I can't speak for others, and their scopes,
      > but I would say that either way, you can't go wrong.
      >
      > I don't have too many pictures with it yet, but the ones I have
      > taken are not too bad considering I am very much a beginner, we have
      > a ton of light pollution in the Chicago area, and I have an
      > inexpensive "monster garaged" Nexstar 114GT mount.
      >
      > See my folder for pictures if you like. The moon pictures are a
      > little soft because seeing conditions were maybe a 2 out 5 that
      > night.
      >
      > Timm
      > --- In William-Optics@yahoogroups.com, "Tim" <tjp314@p...> wrote:
      >
      >>Pardon my ignorance, but I haven't contemplated ordering such a
      >
      > small scope before ;o)...
      >
      >>...but now that I'm interested in a dual wide-field
      >
      > imaging/guidescope to piggyback on my
      >
      >>other scopes (C-8 or C-9.25, most of the time), I was lured in by
      >
      > the compelling ad for the
      >
      >>Megrez 80 II SD.
      >>
      >>Since it's a doublet, what makes it a "semi-apo?" ...and/or what
      >
      > does SD stand for?
      >
      >>Also, anyone able to point me to some wide field deep sky images
      >
      > taken with it?
      >
      >>...should I spring for the ED triplet instead?
      >>
      >>thanks,
      >>-Tim.
      >
      >
      >
      >
      >
      >
      >
      > Yahoo! Groups Links
      >
      >
      >
      >
      >
      >
      >
      >
      >
      >
    • erlend_langsrud
      In Sigma camera lenses, SD stands for Special Dispersion , whereas ED stands for Extra low dispersion . ED is better and more expensive than SD. Some Sigma
      Message 34 of 34 , Oct 9, 2005
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        In Sigma camera lenses, SD stands for "Special Dispersion",
        whereas "ED" stands for "Extra low dispersion". ED is better and
        more expensive than SD. Some Sigma lenses with more than one ED-
        element are labeled APO.

        Nikon uses the term UD (Ultra low Dispersion) which is better than
        ED. UD gives colour correction similar to Fluorite, but it's not the
        same thing as fluorite.

        ....and that's about all I know about expensive glass.

        Erlend

        --- In William-Optics@yahoogroups.com, "willsonjared"
        <willsonjared@y...> wrote:
        >
        > --- In William-Optics@yahoogroups.com, Søren Madsen <Soeren@M...>
        >
        > > So the only read difference between Megrez 80II SD and ED, and
        > > Fluorite APO are that the latter two employ a triplet design
        while the
        > > first is only doublet. The glass used is the same and of the same
        > > quality as, say, TMB uses?
        > > (the f-ratios also vary)
        > >
        > > Sorry if this is a stupid question, I might not have followed the
        > > discussion carefully enough...
        > >
        > > Best Wishes,
        > > Søren Madsen
        > >
        > That can't be the only difference, or what would be the difference
        > between the Flurite and ED triplets?
        >
        > - Jared Willson
        >
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