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Re: SD, ED, FD and Megrez/Zenithstar model differences?

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  • astromfm
    Thanks Timm. I didn t realize the the difference between Megrez and Zenithstar was originally based primarily on color, but that explains why you seem to find
    Message 1 of 4 , Dec 28, 2012
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      Thanks Timm. I didn't realize the the difference between Megrez and Zenithstar was originally based primarily on color, but that explains why you seem to find ED and FD versions in both models. I'm still unclear as to what exactly warrants an ED versus FD designation. I did notice that when FPL-53 glass is used in many FD models WO does indicate that. I do know from a posting I found by William (on this forum) that, at least originally, the Megrez 72FD didn't use Ohara glass so presumably some other glass from another manufacturor with properties between FPL-51 and FPL-53 was used? But as I said, color correction appears to have as much to do with the mating glass and the design so perhaps it's a moot point.

      I just wondered if the FD actually meant anything in particular with regards to my Megrez 72FD (I have the newer DDG version). I've been debating whether I should sell the 72FD and by a triplet, but if my doublet is corrected well enough that may not be necessary. I have done a few test shots and it looks pretty well color corrected in the centre of the field but I don't have the optimal FF/ FR for this scope so stars show CA off axis. I have ordered the new FLAT-6 that is optimized for 70- to 72mm f/6 scopes and I will do some testing when I get it to see if that improves off axis performance.
      ...Keith

      --- In William-Optics@yahoogroups.com, "Timm B" <t.bottoni@...> wrote:
      >
      > Hi Keith,
      >
      > WO actually does reveal on some of the models if they are using a particular glass. The use of ED, SD and FD, along with Fluorite, and other terms are thrown around a lot, and often confused, and there are people that know a lot more about it than I do. Anyway, there is generally a correlation to price, relative to color correction. There are only a couple of glass companies. FPL53 = Ohara and is Japanese, and OK4 = LZOS and is Russian.
      >
      > Doublets vs Triplets gets into another discussion, and I recommend searching CloudyNights.com for more information on glass and refractor designs.
      >
      > The naming on the WO scopes has historically been something like this...
      > Megrez scopes were white - Zenithstar scopes were a shiny anodized aluminum (black or another color). Both families have been offered in equal optical quality, and a number of differences appeared over the years as they evolved.
      >
      > Fluorostar scopes have always been white, and were the top of the line in optics.
      >
      > The 72FD is a very good scope optically, from what I have read in numerous posts. I'm not sure what glass was used in it, but color correction seems quite good from what I can remember.
      >
      > Hope that helps,
      >
      > Timm
      >
      > --- In William-Optics@yahoogroups.com, "astromfm" <eggerk@> wrote:
      > >
      > > I know this has been asked before, but I'm wondering if there are consistent relative differences between ED, SD and FD glass and between Zenithstar and Megrez models. What I've been able to figure out is that at one time ED was FPL-51 type glass, SD was OK4 type glass, and FD was high fluorite FPL-53 type glass. I do understand that WO no longer reveals the type or supplier of the ED glass used in their scopes and that there is much more to color-correction and performance, including the design and type of mating glass. However, despite the different manufacturing sources and glass types, is it correct that in general ED < SD < FD in terms of glass quality, within the constraints of design types (e.g. Doublet or Triplet)? Or is this too simplistic?
      > >
      > > I'm also having a similar problem figuring out the difference between Zenithstar and Megrez Models. From my research I take it that the differences are mostly in the design, with the Megrez being somewhat more robust than the Zenithstar, but again it's hard to see any consistent differences in recent models. So are there consistent model differences?
      > >
      > > It seems like the marketing model has changed to having frequent short runs of new scope models, so maybe the differences between ED/SD/FD and Zenithstar/Megrez have less relevance? Just wondering, as I have a Megrez 72FD that I'm starting to use more for astrophotography and I'm wondering how it compares in the great scheme of things.
      > >
      > > Thanks, Keith
      > >
      >
    • Timm B
      You re welcome Keith, Glad to help. Keep in mind, I m not an employee of WO, but I have been around here a long time, so I m going from memory. There may
      Message 2 of 4 , Dec 29, 2012
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        You're welcome Keith,

        Glad to help. Keep in mind, I'm not an employee of WO, but I have been around here a long time, so I'm going from memory. There may have been other differences besides the color between Megrez and Zenithstar.

        ED vs FD - you are correct, many of the FD scope had FPL-53, At one point, WO had 3 scopes in 66mm. They had an SD doublet, and ED triplet, and an FD doublet. There was an good article, I think in Sky and Telescope, about them, and many reviews written on Astromart and CloudyNights.

        I think that doublet vs triplet is less of an issue, than the actual design and execution of the design. There won't be any difference in field curvature, and both would require a field flattener for astrophotography, as would any doublet or triplet.

        WO has introduced some 5 element scopes (and I think will be introducing more), which have the field flattener built in, and an improved focuser, all with the astrophotographer in mind. As I find out more, I will post information here and on Facebook.

        Timm

        --- In William-Optics@yahoogroups.com, "astromfm" <eggerk@...> wrote:
        >
        > Thanks Timm. I didn't realize the the difference between Megrez and Zenithstar was originally based primarily on color, but that explains why you seem to find ED and FD versions in both models. I'm still unclear as to what exactly warrants an ED versus FD designation. I did notice that when FPL-53 glass is used in many FD models WO does indicate that. I do know from a posting I found by William (on this forum) that, at least originally, the Megrez 72FD didn't use Ohara glass so presumably some other glass from another manufacturor with properties between FPL-51 and FPL-53 was used? But as I said, color correction appears to have as much to do with the mating glass and the design so perhaps it's a moot point.
        >
        > I just wondered if the FD actually meant anything in particular with regards to my Megrez 72FD (I have the newer DDG version). I've been debating whether I should sell the 72FD and by a triplet, but if my doublet is corrected well enough that may not be necessary. I have done a few test shots and it looks pretty well color corrected in the centre of the field but I don't have the optimal FF/ FR for this scope so stars show CA off axis. I have ordered the new FLAT-6 that is optimized for 70- to 72mm f/6 scopes and I will do some testing when I get it to see if that improves off axis performance.
        > ...Keith
        >
        > --- In William-Optics@yahoogroups.com, "Timm B" <t.bottoni@> wrote:
        > >
        > > Hi Keith,
        > >
        > > WO actually does reveal on some of the models if they are using a particular glass. The use of ED, SD and FD, along with Fluorite, and other terms are thrown around a lot, and often confused, and there are people that know a lot more about it than I do. Anyway, there is generally a correlation to price, relative to color correction. There are only a couple of glass companies. FPL53 = Ohara and is Japanese, and OK4 = LZOS and is Russian.
        > >
        > > Doublets vs Triplets gets into another discussion, and I recommend searching CloudyNights.com for more information on glass and refractor designs.
        > >
        > > The naming on the WO scopes has historically been something like this...
        > > Megrez scopes were white - Zenithstar scopes were a shiny anodized aluminum (black or another color). Both families have been offered in equal optical quality, and a number of differences appeared over the years as they evolved.
        > >
        > > Fluorostar scopes have always been white, and were the top of the line in optics.
        > >
        > > The 72FD is a very good scope optically, from what I have read in numerous posts. I'm not sure what glass was used in it, but color correction seems quite good from what I can remember.
        > >
        > > Hope that helps,
        > >
        > > Timm
        > >
        > > --- In William-Optics@yahoogroups.com, "astromfm" <eggerk@> wrote:
        > > >
        > > > I know this has been asked before, but I'm wondering if there are consistent relative differences between ED, SD and FD glass and between Zenithstar and Megrez models. What I've been able to figure out is that at one time ED was FPL-51 type glass, SD was OK4 type glass, and FD was high fluorite FPL-53 type glass. I do understand that WO no longer reveals the type or supplier of the ED glass used in their scopes and that there is much more to color-correction and performance, including the design and type of mating glass. However, despite the different manufacturing sources and glass types, is it correct that in general ED < SD < FD in terms of glass quality, within the constraints of design types (e.g. Doublet or Triplet)? Or is this too simplistic?
        > > >
        > > > I'm also having a similar problem figuring out the difference between Zenithstar and Megrez Models. From my research I take it that the differences are mostly in the design, with the Megrez being somewhat more robust than the Zenithstar, but again it's hard to see any consistent differences in recent models. So are there consistent model differences?
        > > >
        > > > It seems like the marketing model has changed to having frequent short runs of new scope models, so maybe the differences between ED/SD/FD and Zenithstar/Megrez have less relevance? Just wondering, as I have a Megrez 72FD that I'm starting to use more for astrophotography and I'm wondering how it compares in the great scheme of things.
        > > >
        > > > Thanks, Keith
        > > >
        > >
        >
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