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RE: [ccd-newastro] Re: S/N ; F ratio ; and RC vs LX200

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  • Wodaski Yahoo account
    SCTs are very competitive in the planetary imaging area. Such imaging uses only the center of the field of view, and if collimation is very accurate, results
    Message 1 of 26 , Jun 1, 2003
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      SCTs are very competitive in the planetary imaging area. Such imaging uses
      only the center of the field of view, and if collimation is very accurate,
      results will be very good. Where SCTs start to fall down is away from the
      center of the FOV. I have an exceptional 14" SCT (according to folks who
      have a lot of experience with them; I just know that I'm very happy with the
      images it takes). But when I try to go to higher resolutions where RCs do a
      very good job, the SCT doesn't quite have the sharpness in general, and
      especially away from the center of the FOV. RCs do not have coma (they have
      a refractor-like slightly-curved field), so they do much better off-axis
      than SCTs do. The better the seeing, the more likely you are to see these
      differences show up in the images.

      I think my C14 can compete on details at the center of the FOV with just
      about any 12.5" RC image I've seen, but it is clearly inferior away from the
      center on just about any RC image I've seen, irrespective of aperture.

      Ron Wodaski
      author of The New CCD Astronomy
      http://www.newastro.com


      -----Original Message-----
      From: Steve Leikind [mailto:sleikind@...]
      Sent: Sunday, June 01, 2003 1:27 PM
      To: ccd-newastro@yahoogroups.com
      Subject: [ccd-newastro] Re: S/N ; F ratio ; and RC vs LX200


      Randy,

      What you say may well be true, but there are a lot of variables here
      and it's difficult to separate "the wheat from the chaff". Your SCT
      undoubtedly didn't have the same kind of optical quality that your
      Ritchey does. Yet Ed Grafton, Thierry Legault, and Damian Peach have
      taken some extraordinarily good images of Jupiter and Saturn with
      their SCT's and I am not sure that I have seen any with Ritchey's
      that are better even though, for a given aperture, they cost five
      times to ten times more. Some people claim that those guys were
      simply lucky to get good SCT's with outstanding optics. Then I've
      also heard people say that the quality on some of the newer SCT's is
      generally quite good.

      Another variable is collimation. It sounds like Legault collimates
      his 12" every night and often multiple times a night. He has a
      lengthy discussion about collimation and the effects of
      miscollimation on his web site and he underlines his main point
      that "No high resolution result can be hoped without a irreproachable
      collimation". I wonder how many SCT imagers have collimation that
      isn't simply good, but "irreproachable"? Every time an SCT
      mirror "flops" a little, collimation changes with these scopes. I
      suppose that no wanting to constantly recollimate your scope may
      justify the cost differential between Ritchey's and SCT's for many.

      If it's true that there are big differences in the quality of SCT's
      being produced now, perhaps it makes sense to buy one new from a
      retailer who accepts returns if you are not satisfied. Then you keep
      returning them until you find one with superior quality. If you have
      the patience for this, perhaps you would be rewarded by getting a
      scope that's as good as a Ritchey (on-axis) at 10% of the cost???

      It's also possible that people like Legault and Grafton are so much
      better at taking and processing planetary images that they maximize
      the potential of their scopes, while people with superior optics have
      not managed to do that. It would be nice to get the whole story on
      this, but I am not sure we ever will.

      Steve

      --- In ccd-newastro@yahoogroups.com, "Randy Nulman" <rj.nulman@v...>
      wrote:
      > I saw the same thing when I got my 12.5 RC. The optics of my old
      C11
      > were relatively good, but my fwhm improved by almost 25% with the
      RC!
      > (This was comparing "on axis" stars for both scopes)
      >
      > I was originally expecting only an "off axis" improvement, but the
      > quality of the optics in the RCOS really made a difference.
      >
      > Randy Nulman
      >
      > --- In ccd-newastro@yahoogroups.com, "Wodaski Yahoo account"
      > <yahoo@w...> wrote:
      > > It has been my experience, both visually and with CCD, that poor
      > optics are
      > > more affected by seeing that good optics.
      > >
      > > An interesting case in point: On a night of exceptional seeing at
      > New Mexico
      > > Skies, I took an image of M51 with the C14 and ST-10 binned 2x2
      > that was
      > > very good. Still a little soft, however. In the first tests of
      the
      > new 20"
      > > RC, on a night that was so bad I didn't bother to image with the
      > C14, the
      > > images of M51 were as good as they were on that best night with
      the
      > C14 -
      > > despite the fact that we are still making adjustments to the RC
      and
      > it's
      > > mounting to improve performance. This fact just blew me away.
      > >
      > > Ron Wodaski
      > > author of The New CCD Astronomy
      > > http://www.newastro.com
      > >
      > >
      > > -----Original Message-----
      > > From: clearviewh [mailto:clearview@c...]
      > > Sent: Saturday, May 31, 2003 8:13 PM
      > > To: ccd-newastro@yahoogroups.com
      > > Subject: [ccd-newastro] Re: S/N ; F ratio ; and RC vs LX200
      > >
      > >
      > > To tell you the truth, I think a LOT of it is location. Sometimes
      I
      > > whine about not having the money for a nice RC and Paramount mount
      > > but I have spent plenty on the domed observatory. Thing is, I
      wonder
      > > if I would get full value out of that kind of setup here. When
      > seeing
      > > is good, which is not that often, I get images that I am very
      proud
      > > of. The rest of the time, as I watch the guide star jumping around
      > > from poor seeing, I wonder just how well even a Paramount would
      > > perform here.....at least that's what I keep telling myself....
      LOL
      > > Ed
      > >
      > > --- In ccd-newastro@yahoogroups.com, "Mark de Regt" <deregt@e...>
      > > wrote:
      > > > Ed,
      > > >
      > > > This is something I have thought a lot about, and talked with
      > > people with
      > > > experience with both SCTs and RCs. I believe, of course, that
      the
      > > RC optics
      > > > are better than my LX200, but I also believet that my LX200 has
      > > excellent
      > > > optics. When you talk about the RC images you see, it is worth
      > > keeping in
      > > > mind that people with RCs tend to be experienced imagers, and
      > often
      > > have
      > > > superior locations. Taking nothing away from Adam Block at Kitt
      > > Peak (whose
      > > > images have become routinely sublime, they are so wonderful),
      and
      > > others, it
      > > > is also worth remembering that their scopes are bigger than
      most
      > of
      > > ours.
      > > > Most of the RCs you see are 12.5 inch, with some at 14.5 inch,
      16
      > > inch, and
      > > > Adam now uses a 20 inch. I know that emulsion photographers say
      > > that focal
      > > > ratio is the sole determiner of exposure length, but, with CCD
      > > imaging of
      > > > the heavens, I don't believe it--The larger the aperture, the
      less
      > > time it
      > > > takes to get good S/N, I think. Add to that the superior
      location
      > > someone
      > > > like Adam has--no light pollution and 7000 foot elevation, and
      you
      > > can't
      > > > even compare that circumstance to what most of us deal with.
      Add
      > > to that
      > > > the fact the many of the best imagers manage to get several
      images
      > > a month
      > > > (at least), year round, while I'm happy if I get ten in a year;
      > the
      > > > experience in image acquisition and image processing, and its
      > > contribution
      > > > to the final result, should not be underestimated,
      > > >
      > > > I think that the optics themselves plays a pretty minor role in
      > > what you see
      > > > with exposure length; the steadier mount is more important, but
      > the
      > > AO-7
      > > > makes up for most of that. I believe that dark skies,
      elevation,
      > > and larger
      > > > aperture has a lot more to do with it than RC quality.
      > > >
      > > >
      > > >
      > > > > -----Original Message-----
      > > > > From: clearviewh [mailto:clearview@c...]
      > > > > Sent: Saturday, May 31, 2003 6:00 PM
      > > > > To: ccd-newastro@yahoogroups.com
      > > > > Subject: [ccd-newastro] S/N ; F ratio ; and RC vs LX200
      > > > >
      > > > >
      > > > > Just wanted to take this opportunity, while Ron is apparently
      > > gone,
      > > > > to comment on the question of S/N only being related to F.R.
      I
      > > have
      > > > > known for a long time, that with my LX200, I have to take MUCH
      > > longer
      > > > > exposure times than someone with say an RC on a Paramount
      with
      > the
      > > > > same FL and diameter. I have gone round and round on the
      subject
      > > and
      > > > > finally deceided that the QUALITY of the setup ALSO plays a
      role
      > > in
      > > > > S/N. Perhaps not, I agree, in the ACTUAL S/N, but a better
      setup
      > > > > spreads the signal around less, giving a better image. I have
      to
      > > take
      > > > > a much longer exposures cause the poorer tracking, and
      optics,
      > of
      > > my
      > > > > LX200, spreads my signal out more..... bloated
      stars.....etc.
      > So
      > > > > when say a Rob Gendler with his 12 in RC at F9 takes a
      L:R:G:B
      > of
      > > > > 120:40:60:60, I have to take a 180:60:90:90 to get an image
      that
      > > > > appears to have a similar S/N even at F5....Comments??
      > > > > Ed
      > > > >
      > > > >
      > > > >
      > > > > To unsubscribe from this group, send an email to:
      > > > > ccd-newastro-unsubscribe@egroups.com
      > > > >
      > > > >
      > > > >
      > > > > Your use of Yahoo! Groups is subject to
      > > http://docs.yahoo.com/info/terms/
      > > > >
      > > > >
      > >
      > >
      > >
      > > To unsubscribe from this group, send an email to:
      > > ccd-newastro-unsubscribe@egroups.com
      > >
      > >
      > >
      > > Your use of Yahoo! Groups is subject to
      > http://docs.yahoo.com/info/terms/



      To unsubscribe from this group, send an email to:
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    • clearviewh
      I suppose that s why I am more pleased with objects that don t fill more than the center portion of the FOV and seem a little more wide angle than I am with
      Message 2 of 26 , Jun 1, 2003
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        I suppose that's why I am more pleased with objects that don't fill
        more than the center portion of the FOV and seem a little more "wide
        angle" than I am with a try at a high res galaxy that fills the whole
        frame.....
        Ed

        --- In ccd-newastro@yahoogroups.com, "Wodaski Yahoo account"
        <yahoo@w...> wrote:
        > SCTs are very competitive in the planetary imaging area. Such
        imaging uses
        > only the center of the field of view, and if collimation is very
        accurate,
        > results will be very good. Where SCTs start to fall down is away
        from the
        > center of the FOV. I have an exceptional 14" SCT (according to
        folks who
        > have a lot of experience with them; I just know that I'm very happy
        with the
        > images it takes). But when I try to go to higher resolutions where
        RCs do a
        > very good job, the SCT doesn't quite have the sharpness in general,
        and
        > especially away from the center of the FOV. RCs do not have coma
        (they have
        > a refractor-like slightly-curved field), so they do much better off-
        axis
        > than SCTs do. The better the seeing, the more likely you are to see
        these
        > differences show up in the images.
        >
        > I think my C14 can compete on details at the center of the FOV with
        just
        > about any 12.5" RC image I've seen, but it is clearly inferior away
        from the
        > center on just about any RC image I've seen, irrespective of
        aperture.
        >
        > Ron Wodaski
        > author of The New CCD Astronomy
        > http://www.newastro.com
        >
        >
        > -----Original Message-----
        > From: Steve Leikind [mailto:sleikind@v...]
        > Sent: Sunday, June 01, 2003 1:27 PM
        > To: ccd-newastro@yahoogroups.com
        > Subject: [ccd-newastro] Re: S/N ; F ratio ; and RC vs LX200
        >
        >
        > Randy,
        >
        > What you say may well be true, but there are a lot of variables here
        > and it's difficult to separate "the wheat from the chaff". Your SCT
        > undoubtedly didn't have the same kind of optical quality that your
        > Ritchey does. Yet Ed Grafton, Thierry Legault, and Damian Peach have
        > taken some extraordinarily good images of Jupiter and Saturn with
        > their SCT's and I am not sure that I have seen any with Ritchey's
        > that are better even though, for a given aperture, they cost five
        > times to ten times more. Some people claim that those guys were
        > simply lucky to get good SCT's with outstanding optics. Then I've
        > also heard people say that the quality on some of the newer SCT's is
        > generally quite good.
        >
        > Another variable is collimation. It sounds like Legault collimates
        > his 12" every night and often multiple times a night. He has a
        > lengthy discussion about collimation and the effects of
        > miscollimation on his web site and he underlines his main point
        > that "No high resolution result can be hoped without a
        irreproachable
        > collimation". I wonder how many SCT imagers have collimation that
        > isn't simply good, but "irreproachable"? Every time an SCT
        > mirror "flops" a little, collimation changes with these scopes. I
        > suppose that no wanting to constantly recollimate your scope may
        > justify the cost differential between Ritchey's and SCT's for many.
        >
        > If it's true that there are big differences in the quality of SCT's
        > being produced now, perhaps it makes sense to buy one new from a
        > retailer who accepts returns if you are not satisfied. Then you keep
        > returning them until you find one with superior quality. If you have
        > the patience for this, perhaps you would be rewarded by getting a
        > scope that's as good as a Ritchey (on-axis) at 10% of the cost???
        >
        > It's also possible that people like Legault and Grafton are so much
        > better at taking and processing planetary images that they maximize
        > the potential of their scopes, while people with superior optics
        have
        > not managed to do that. It would be nice to get the whole story on
        > this, but I am not sure we ever will.
        >
        > Steve
        >
        > --- In ccd-newastro@yahoogroups.com, "Randy Nulman" <rj.nulman@v...>
        > wrote:
        > > I saw the same thing when I got my 12.5 RC. The optics of my old
        > C11
        > > were relatively good, but my fwhm improved by almost 25% with the
        > RC!
        > > (This was comparing "on axis" stars for both scopes)
        > >
        > > I was originally expecting only an "off axis" improvement, but the
        > > quality of the optics in the RCOS really made a difference.
        > >
        > > Randy Nulman
        > >
        > > --- In ccd-newastro@yahoogroups.com, "Wodaski Yahoo account"
        > > <yahoo@w...> wrote:
        > > > It has been my experience, both visually and with CCD, that poor
        > > optics are
        > > > more affected by seeing that good optics.
        > > >
        > > > An interesting case in point: On a night of exceptional seeing
        at
        > > New Mexico
        > > > Skies, I took an image of M51 with the C14 and ST-10 binned 2x2
        > > that was
        > > > very good. Still a little soft, however. In the first tests of
        > the
        > > new 20"
        > > > RC, on a night that was so bad I didn't bother to image with the
        > > C14, the
        > > > images of M51 were as good as they were on that best night with
        > the
        > > C14 -
        > > > despite the fact that we are still making adjustments to the RC
        > and
        > > it's
        > > > mounting to improve performance. This fact just blew me away.
        > > >
        > > > Ron Wodaski
        > > > author of The New CCD Astronomy
        > > > http://www.newastro.com
        > > >
        > > >
        > > > -----Original Message-----
        > > > From: clearviewh [mailto:clearview@c...]
        > > > Sent: Saturday, May 31, 2003 8:13 PM
        > > > To: ccd-newastro@yahoogroups.com
        > > > Subject: [ccd-newastro] Re: S/N ; F ratio ; and RC vs LX200
        > > >
        > > >
        > > > To tell you the truth, I think a LOT of it is location.
        Sometimes
        > I
        > > > whine about not having the money for a nice RC and Paramount
        mount
        > > > but I have spent plenty on the domed observatory. Thing is, I
        > wonder
        > > > if I would get full value out of that kind of setup here. When
        > > seeing
        > > > is good, which is not that often, I get images that I am very
        > proud
        > > > of. The rest of the time, as I watch the guide star jumping
        around
        > > > from poor seeing, I wonder just how well even a Paramount would
        > > > perform here.....at least that's what I keep telling myself....
        > LOL
        > > > Ed
        > > >
        > > > --- In ccd-newastro@yahoogroups.com, "Mark de Regt"
        <deregt@e...>
        > > > wrote:
        > > > > Ed,
        > > > >
        > > > > This is something I have thought a lot about, and talked with
        > > > people with
        > > > > experience with both SCTs and RCs. I believe, of course, that
        > the
        > > > RC optics
        > > > > are better than my LX200, but I also believet that my LX200
        has
        > > > excellent
        > > > > optics. When you talk about the RC images you see, it is
        worth
        > > > keeping in
        > > > > mind that people with RCs tend to be experienced imagers, and
        > > often
        > > > have
        > > > > superior locations. Taking nothing away from Adam Block at
        Kitt
        > > > Peak (whose
        > > > > images have become routinely sublime, they are so wonderful),
        > and
        > > > others, it
        > > > > is also worth remembering that their scopes are bigger than
        > most
        > > of
        > > > ours.
        > > > > Most of the RCs you see are 12.5 inch, with some at 14.5 inch,
        > 16
        > > > inch, and
        > > > > Adam now uses a 20 inch. I know that emulsion photographers
        say
        > > > that focal
        > > > > ratio is the sole determiner of exposure length, but, with CCD
        > > > imaging of
        > > > > the heavens, I don't believe it--The larger the aperture, the
        > less
        > > > time it
        > > > > takes to get good S/N, I think. Add to that the superior
        > location
        > > > someone
        > > > > like Adam has--no light pollution and 7000 foot elevation, and
        > you
        > > > can't
        > > > > even compare that circumstance to what most of us deal with.
        > Add
        > > > to that
        > > > > the fact the many of the best imagers manage to get several
        > images
        > > > a month
        > > > > (at least), year round, while I'm happy if I get ten in a
        year;
        > > the
        > > > > experience in image acquisition and image processing, and its
        > > > contribution
        > > > > to the final result, should not be underestimated,
        > > > >
        > > > > I think that the optics themselves plays a pretty minor role
        in
        > > > what you see
        > > > > with exposure length; the steadier mount is more important,
        but
        > > the
        > > > AO-7
        > > > > makes up for most of that. I believe that dark skies,
        > elevation,
        > > > and larger
        > > > > aperture has a lot more to do with it than RC quality.
        > > > >
        > > > >
        > > > >
        > > > > > -----Original Message-----
        > > > > > From: clearviewh [mailto:clearview@c...]
        > > > > > Sent: Saturday, May 31, 2003 6:00 PM
        > > > > > To: ccd-newastro@yahoogroups.com
        > > > > > Subject: [ccd-newastro] S/N ; F ratio ; and RC vs LX200
        > > > > >
        > > > > >
        > > > > > Just wanted to take this opportunity, while Ron is
        apparently
        > > > gone,
        > > > > > to comment on the question of S/N only being related to F.R.
        > I
        > > > have
        > > > > > known for a long time, that with my LX200, I have to take
        MUCH
        > > > longer
        > > > > > exposure times than someone with say an RC on a Paramount
        > with
        > > the
        > > > > > same FL and diameter. I have gone round and round on the
        > subject
        > > > and
        > > > > > finally deceided that the QUALITY of the setup ALSO plays a
        > role
        > > > in
        > > > > > S/N. Perhaps not, I agree, in the ACTUAL S/N, but a better
        > setup
        > > > > > spreads the signal around less, giving a better image. I
        have
        > to
        > > > take
        > > > > > a much longer exposures cause the poorer tracking, and
        > optics,
        > > of
        > > > my
        > > > > > LX200, spreads my signal out more..... bloated
        > stars.....etc.
        > > So
        > > > > > when say a Rob Gendler with his 12 in RC at F9 takes a
        > L:R:G:B
        > > of
        > > > > > 120:40:60:60, I have to take a 180:60:90:90 to get an image
        > that
        > > > > > appears to have a similar S/N even at F5....Comments??
        > > > > > Ed
        > > > > >
        > > > > >
        > > > > >
        > > > > > To unsubscribe from this group, send an email to:
        > > > > > ccd-newastro-unsubscribe@egroups.com
        > > > > >
        > > > > >
        > > > > >
        > > > > > Your use of Yahoo! Groups is subject to
        > > > http://docs.yahoo.com/info/terms/
        > > > > >
        > > > > >
        > > >
        > > >
        > > >
        > > > To unsubscribe from this group, send an email to:
        > > > ccd-newastro-unsubscribe@egroups.com
        > > >
        > > >
        > > >
        > > > Your use of Yahoo! Groups is subject to
        > > http://docs.yahoo.com/info/terms/
        >
        >
        >
        > To unsubscribe from this group, send an email to:
        > ccd-newastro-unsubscribe@egroups.com
        >
        >
        >
        > Your use of Yahoo! Groups is subject to
        http://docs.yahoo.com/info/terms/
      • Steve Leikind
        Ron, This makes sense. It would be nice to know how much variability there is in the quality of SCT s at this time, but any information we can get about this
        Message 3 of 26 , Jun 1, 2003
        • 0 Attachment
          Ron,

          This makes sense. It would be nice to know how much variability there
          is in the quality of SCT's at this time, but any information we can
          get about this is probably anecdotal. Obviously, you managed to get
          an SCT which others regard as among the cream of the crop.

          I am curious as to how Mewlon's and other designs (Mak-Newt; Mak-
          Cass) compete with Ritchey's on-axis and off. I have read claims that
          Ritchey's do not produce the best on-axis images, but I cannot
          remember where. Obviously, there are trade-offs with some of the
          other designs such as f-ratio, bulk etc. where Ritchey's have an edge.

          Steve

          --- In ccd-newastro@yahoogroups.com, "Wodaski Yahoo account"
          <yahoo@w...> wrote:
          > SCTs are very competitive in the planetary imaging area. Such
          imaging uses
          > only the center of the field of view, and if collimation is very
          accurate,
          > results will be very good. Where SCTs start to fall down is away
          from the
          > center of the FOV. I have an exceptional 14" SCT (according to
          folks who
          > have a lot of experience with them; I just know that I'm very happy
          with the
          > images it takes). But when I try to go to higher resolutions where
          RCs do a
          > very good job, the SCT doesn't quite have the sharpness in general,
          and
          > especially away from the center of the FOV. RCs do not have coma
          (they have
          > a refractor-like slightly-curved field), so they do much better off-
          axis
          > than SCTs do. The better the seeing, the more likely you are to see
          these
          > differences show up in the images.
          >
          > I think my C14 can compete on details at the center of the FOV with
          just
          > about any 12.5" RC image I've seen, but it is clearly inferior away
          from the
          > center on just about any RC image I've seen, irrespective of
          aperture.
          >
          > Ron Wodaski
          > author of The New CCD Astronomy
          > http://www.newastro.com
          >
          >
          > -----Original Message-----
          > From: Steve Leikind [mailto:sleikind@v...]
          > Sent: Sunday, June 01, 2003 1:27 PM
          > To: ccd-newastro@yahoogroups.com
          > Subject: [ccd-newastro] Re: S/N ; F ratio ; and RC vs LX200
          >
          >
          > Randy,
          >
          > What you say may well be true, but there are a lot of variables here
          > and it's difficult to separate "the wheat from the chaff". Your SCT
          > undoubtedly didn't have the same kind of optical quality that your
          > Ritchey does. Yet Ed Grafton, Thierry Legault, and Damian Peach have
          > taken some extraordinarily good images of Jupiter and Saturn with
          > their SCT's and I am not sure that I have seen any with Ritchey's
          > that are better even though, for a given aperture, they cost five
          > times to ten times more. Some people claim that those guys were
          > simply lucky to get good SCT's with outstanding optics. Then I've
          > also heard people say that the quality on some of the newer SCT's is
          > generally quite good.
          >
          > Another variable is collimation. It sounds like Legault collimates
          > his 12" every night and often multiple times a night. He has a
          > lengthy discussion about collimation and the effects of
          > miscollimation on his web site and he underlines his main point
          > that "No high resolution result can be hoped without a
          irreproachable
          > collimation". I wonder how many SCT imagers have collimation that
          > isn't simply good, but "irreproachable"? Every time an SCT
          > mirror "flops" a little, collimation changes with these scopes. I
          > suppose that no wanting to constantly recollimate your scope may
          > justify the cost differential between Ritchey's and SCT's for many.
          >
          > If it's true that there are big differences in the quality of SCT's
          > being produced now, perhaps it makes sense to buy one new from a
          > retailer who accepts returns if you are not satisfied. Then you keep
          > returning them until you find one with superior quality. If you have
          > the patience for this, perhaps you would be rewarded by getting a
          > scope that's as good as a Ritchey (on-axis) at 10% of the cost???
          >
          > It's also possible that people like Legault and Grafton are so much
          > better at taking and processing planetary images that they maximize
          > the potential of their scopes, while people with superior optics
          have
          > not managed to do that. It would be nice to get the whole story on
          > this, but I am not sure we ever will.
          >
          > Steve
          >
          > --- In ccd-newastro@yahoogroups.com, "Randy Nulman" <rj.nulman@v...>
          > wrote:
          > > I saw the same thing when I got my 12.5 RC. The optics of my old
          > C11
          > > were relatively good, but my fwhm improved by almost 25% with the
          > RC!
          > > (This was comparing "on axis" stars for both scopes)
          > >
          > > I was originally expecting only an "off axis" improvement, but the
          > > quality of the optics in the RCOS really made a difference.
          > >
          > > Randy Nulman
          > >
          > > --- In ccd-newastro@yahoogroups.com, "Wodaski Yahoo account"
          > > <yahoo@w...> wrote:
          > > > It has been my experience, both visually and with CCD, that poor
          > > optics are
          > > > more affected by seeing that good optics.
          > > >
          > > > An interesting case in point: On a night of exceptional seeing
          at
          > > New Mexico
          > > > Skies, I took an image of M51 with the C14 and ST-10 binned 2x2
          > > that was
          > > > very good. Still a little soft, however. In the first tests of
          > the
          > > new 20"
          > > > RC, on a night that was so bad I didn't bother to image with the
          > > C14, the
          > > > images of M51 were as good as they were on that best night with
          > the
          > > C14 -
          > > > despite the fact that we are still making adjustments to the RC
          > and
          > > it's
          > > > mounting to improve performance. This fact just blew me away.
          > > >
          > > > Ron Wodaski
          > > > author of The New CCD Astronomy
          > > > http://www.newastro.com
          > > >
          > > >
          > > > -----Original Message-----
          > > > From: clearviewh [mailto:clearview@c...]
          > > > Sent: Saturday, May 31, 2003 8:13 PM
          > > > To: ccd-newastro@yahoogroups.com
          > > > Subject: [ccd-newastro] Re: S/N ; F ratio ; and RC vs LX200
          > > >
          > > >
          > > > To tell you the truth, I think a LOT of it is location.
          Sometimes
          > I
          > > > whine about not having the money for a nice RC and Paramount
          mount
          > > > but I have spent plenty on the domed observatory. Thing is, I
          > wonder
          > > > if I would get full value out of that kind of setup here. When
          > > seeing
          > > > is good, which is not that often, I get images that I am very
          > proud
          > > > of. The rest of the time, as I watch the guide star jumping
          around
          > > > from poor seeing, I wonder just how well even a Paramount would
          > > > perform here.....at least that's what I keep telling myself....
          > LOL
          > > > Ed
          > > >
          > > > --- In ccd-newastro@yahoogroups.com, "Mark de Regt"
          <deregt@e...>
          > > > wrote:
          > > > > Ed,
          > > > >
          > > > > This is something I have thought a lot about, and talked with
          > > > people with
          > > > > experience with both SCTs and RCs. I believe, of course, that
          > the
          > > > RC optics
          > > > > are better than my LX200, but I also believet that my LX200
          has
          > > > excellent
          > > > > optics. When you talk about the RC images you see, it is
          worth
          > > > keeping in
          > > > > mind that people with RCs tend to be experienced imagers, and
          > > often
          > > > have
          > > > > superior locations. Taking nothing away from Adam Block at
          Kitt
          > > > Peak (whose
          > > > > images have become routinely sublime, they are so wonderful),
          > and
          > > > others, it
          > > > > is also worth remembering that their scopes are bigger than
          > most
          > > of
          > > > ours.
          > > > > Most of the RCs you see are 12.5 inch, with some at 14.5 inch,
          > 16
          > > > inch, and
          > > > > Adam now uses a 20 inch. I know that emulsion photographers
          say
          > > > that focal
          > > > > ratio is the sole determiner of exposure length, but, with CCD
          > > > imaging of
          > > > > the heavens, I don't believe it--The larger the aperture, the
          > less
          > > > time it
          > > > > takes to get good S/N, I think. Add to that the superior
          > location
          > > > someone
          > > > > like Adam has--no light pollution and 7000 foot elevation, and
          > you
          > > > can't
          > > > > even compare that circumstance to what most of us deal with.
          > Add
          > > > to that
          > > > > the fact the many of the best imagers manage to get several
          > images
          > > > a month
          > > > > (at least), year round, while I'm happy if I get ten in a
          year;
          > > the
          > > > > experience in image acquisition and image processing, and its
          > > > contribution
          > > > > to the final result, should not be underestimated,
          > > > >
          > > > > I think that the optics themselves plays a pretty minor role
          in
          > > > what you see
          > > > > with exposure length; the steadier mount is more important,
          but
          > > the
          > > > AO-7
          > > > > makes up for most of that. I believe that dark skies,
          > elevation,
          > > > and larger
          > > > > aperture has a lot more to do with it than RC quality.
          > > > >
          > > > >
          > > > >
          > > > > > -----Original Message-----
          > > > > > From: clearviewh [mailto:clearview@c...]
          > > > > > Sent: Saturday, May 31, 2003 6:00 PM
          > > > > > To: ccd-newastro@yahoogroups.com
          > > > > > Subject: [ccd-newastro] S/N ; F ratio ; and RC vs LX200
          > > > > >
          > > > > >
          > > > > > Just wanted to take this opportunity, while Ron is
          apparently
          > > > gone,
          > > > > > to comment on the question of S/N only being related to F.R.
          > I
          > > > have
          > > > > > known for a long time, that with my LX200, I have to take
          MUCH
          > > > longer
          > > > > > exposure times than someone with say an RC on a Paramount
          > with
          > > the
          > > > > > same FL and diameter. I have gone round and round on the
          > subject
          > > > and
          > > > > > finally deceided that the QUALITY of the setup ALSO plays a
          > role
          > > > in
          > > > > > S/N. Perhaps not, I agree, in the ACTUAL S/N, but a better
          > setup
          > > > > > spreads the signal around less, giving a better image. I
          have
          > to
          > > > take
          > > > > > a much longer exposures cause the poorer tracking, and
          > optics,
          > > of
          > > > my
          > > > > > LX200, spreads my signal out more..... bloated
          > stars.....etc.
          > > So
          > > > > > when say a Rob Gendler with his 12 in RC at F9 takes a
          > L:R:G:B
          > > of
          > > > > > 120:40:60:60, I have to take a 180:60:90:90 to get an image
          > that
          > > > > > appears to have a similar S/N even at F5....Comments??
          > > > > > Ed
          > > > > >
          > > > > >
          > > > > >
          > > > > > To unsubscribe from this group, send an email to:
          > > > > > ccd-newastro-unsubscribe@egroups.com
          > > > > >
          > > > > >
          > > > > >
          > > > > > Your use of Yahoo! Groups is subject to
          > > > http://docs.yahoo.com/info/terms/
          > > > > >
          > > > > >
          > > >
          > > >
          > > >
          > > > To unsubscribe from this group, send an email to:
          > > > ccd-newastro-unsubscribe@egroups.com
          > > >
          > > >
          > > >
          > > > Your use of Yahoo! Groups is subject to
          > > http://docs.yahoo.com/info/terms/
          >
          >
          >
          > To unsubscribe from this group, send an email to:
          > ccd-newastro-unsubscribe@egroups.com
          >
          >
          >
          > Your use of Yahoo! Groups is subject to
          http://docs.yahoo.com/info/terms/
        • Chris Johnston
          Gents All very interesting comments. It seems that excellent on axis images are taken by the experts mentioned, although I note that Damian Peach is now buying
          Message 4 of 26 , Jun 1, 2003
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            Gents

            All very interesting comments.

            It seems that excellent on axis images are taken by the experts
            mentioned, although I note that Damian Peach is now buying a Mewlon
            250. From what I have read and seen it appears that to get good
            images from a commercial SCT, assuming you get reasonable optics in
            the first instance, you need to collimate continuously as well as
            correct for mirror flop.

            However, for those of us who have no wish to continuously collimate
            and who have no wish to combat mirror flop, the Mewlon is a
            compromise between the commercial SCT and the expensive RC. If will
            give equal on axis performance but has about the same coma off axis
            as the SCT. Of course there is also just about 100% assurance of
            getting a good scope out of the box.

            The comment that ten times the price should bring ten times the
            quality of images was interesting, as this would not be paralleled in
            any other capital items. Take for instance a motor vehicle. Does
            the BMW give the commensurate amount of quality as compared to the
            mass produced sedan. Nowhere near it I would have thought. Yet
            there is an active market for BMWs. It appears that there is no
            shortage of people who will pay that singificant amount more for the
            small amount of extra quality. Hell, I am one of them.

            Cheers
            Chris
          • clearviewh
            It appears that there is no ... the ... Ah lets celebrate our differences then, for I am not LOL course my Toyato truck cost 17,000. I wouldn t pay 170,000
            Message 5 of 26 , Jun 2, 2003
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              It appears that there is no
              > shortage of people who will pay that singificant amount more for
              the
              > small amount of extra quality. Hell, I am one of them.
              >
              > Cheers
              > Chris

              Ah lets celebrate our differences then, for I am not LOL
              course my Toyato truck cost 17,000. I wouldn't pay 170,000 for
              just a slightly better one :<)
              Ed
            • clearviewh
              ... .....course it s not THAT much of a battle, last nights precollamtion took 4 minutes, and the lock for the mirror cost 18.00 not bad investment to save
              Message 6 of 26 , Jun 2, 2003
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                >
                > However, for those of us who have no wish to continuously collimate
                > and who have no wish to combat mirror flop,
                .....course it's not THAT much of a battle, last nights
                precollamtion took 4 minutes, and the lock for the mirror cost 18.00
                not bad investment to save 20,000 and look at what I got for my
                trouble
                http://www.cuttingedge.net/~clearview/images/m27.htm
              • Chris Johnston
                Ed In regard to the Toyota I would agree with you. My Toyota 4 wheel drive cost new not much more than your truck. Yet I often see many Lexus 4 wheel drives
                Message 7 of 26 , Jun 2, 2003
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                  Ed

                  In regard to the Toyota I would agree with you. My Toyota 4 wheel
                  drive cost new not much more than your truck. Yet I often see many
                  Lexus 4 wheel drives around the place that cost four times as much.
                  Damned if I can make out the difference.

                  Chris
                • Wodaski Yahoo account
                  I think there is less variability than in the past, but I do not know how one could quantify it because most of the data is, as you note, anecdotal. The
                  Message 8 of 26 , Jun 3, 2003
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                    I think there is less variability than in the past, but I do not know how
                    one could quantify it because most of the data is, as you note, anecdotal.

                    The Mewlons are very good optically. They have coma, like most Cassegrain
                    designs, but have superb on-axis and near-axis performance. They are very
                    refractor-like, with just a shade less contrast than a superb refractor.
                    Last I looked, however, 8-10" refractors were, um, a bit more expensive than
                    a Mewlon. <g>

                    I can see where a Ritchie might not have the absolute best on-axis
                    performance since it is optimized for overall field performance. But it's
                    still very good. A high-end Newtonian might do better at central spot size,
                    but of course fast Newt's have really noticeable coma. The difference with
                    the Ritchie-Chretien is that it uses hyperbolic (instead of the more easily
                    made spherical or parabolic) mirrors. This allows designs that eliminate
                    coma.

                    For really large flat fields, an RC requires a corrector (just as a high-end
                    refractor might require a flattener). But for most CCD chips, flatness of
                    field is not an issue. Larger film formats require a corrector, such as that
                    found on the Takahashi BRC.

                    Ron Wodaski
                    author of The New CCD Astronomy
                    http://www.newastro.com


                    -----Original Message-----
                    From: Steve Leikind [mailto:sleikind@...]
                    Sent: Sunday, June 01, 2003 4:46 PM
                    To: ccd-newastro@yahoogroups.com
                    Subject: [ccd-newastro] Re: S/N ; F ratio ; and RC vs LX200


                    Ron,

                    This makes sense. It would be nice to know how much variability there
                    is in the quality of SCT's at this time, but any information we can
                    get about this is probably anecdotal. Obviously, you managed to get
                    an SCT which others regard as among the cream of the crop.

                    I am curious as to how Mewlon's and other designs (Mak-Newt; Mak-
                    Cass) compete with Ritchey's on-axis and off. I have read claims that
                    Ritchey's do not produce the best on-axis images, but I cannot
                    remember where. Obviously, there are trade-offs with some of the
                    other designs such as f-ratio, bulk etc. where Ritchey's have an edge.

                    Steve

                    --- In ccd-newastro@yahoogroups.com, "Wodaski Yahoo account"
                    <yahoo@w...> wrote:
                    > SCTs are very competitive in the planetary imaging area. Such
                    imaging uses
                    > only the center of the field of view, and if collimation is very
                    accurate,
                    > results will be very good. Where SCTs start to fall down is away
                    from the
                    > center of the FOV. I have an exceptional 14" SCT (according to
                    folks who
                    > have a lot of experience with them; I just know that I'm very happy
                    with the
                    > images it takes). But when I try to go to higher resolutions where
                    RCs do a
                    > very good job, the SCT doesn't quite have the sharpness in general,
                    and
                    > especially away from the center of the FOV. RCs do not have coma
                    (they have
                    > a refractor-like slightly-curved field), so they do much better off-
                    axis
                    > than SCTs do. The better the seeing, the more likely you are to see
                    these
                    > differences show up in the images.
                    >
                    > I think my C14 can compete on details at the center of the FOV with
                    just
                    > about any 12.5" RC image I've seen, but it is clearly inferior away
                    from the
                    > center on just about any RC image I've seen, irrespective of
                    aperture.
                    >
                    > Ron Wodaski
                    > author of The New CCD Astronomy
                    > http://www.newastro.com
                    >
                    >
                    > -----Original Message-----
                    > From: Steve Leikind [mailto:sleikind@v...]
                    > Sent: Sunday, June 01, 2003 1:27 PM
                    > To: ccd-newastro@yahoogroups.com
                    > Subject: [ccd-newastro] Re: S/N ; F ratio ; and RC vs LX200
                    >
                    >
                    > Randy,
                    >
                    > What you say may well be true, but there are a lot of variables here
                    > and it's difficult to separate "the wheat from the chaff". Your SCT
                    > undoubtedly didn't have the same kind of optical quality that your
                    > Ritchey does. Yet Ed Grafton, Thierry Legault, and Damian Peach have
                    > taken some extraordinarily good images of Jupiter and Saturn with
                    > their SCT's and I am not sure that I have seen any with Ritchey's
                    > that are better even though, for a given aperture, they cost five
                    > times to ten times more. Some people claim that those guys were
                    > simply lucky to get good SCT's with outstanding optics. Then I've
                    > also heard people say that the quality on some of the newer SCT's is
                    > generally quite good.
                    >
                    > Another variable is collimation. It sounds like Legault collimates
                    > his 12" every night and often multiple times a night. He has a
                    > lengthy discussion about collimation and the effects of
                    > miscollimation on his web site and he underlines his main point
                    > that "No high resolution result can be hoped without a
                    irreproachable
                    > collimation". I wonder how many SCT imagers have collimation that
                    > isn't simply good, but "irreproachable"? Every time an SCT
                    > mirror "flops" a little, collimation changes with these scopes. I
                    > suppose that no wanting to constantly recollimate your scope may
                    > justify the cost differential between Ritchey's and SCT's for many.
                    >
                    > If it's true that there are big differences in the quality of SCT's
                    > being produced now, perhaps it makes sense to buy one new from a
                    > retailer who accepts returns if you are not satisfied. Then you keep
                    > returning them until you find one with superior quality. If you have
                    > the patience for this, perhaps you would be rewarded by getting a
                    > scope that's as good as a Ritchey (on-axis) at 10% of the cost???
                    >
                    > It's also possible that people like Legault and Grafton are so much
                    > better at taking and processing planetary images that they maximize
                    > the potential of their scopes, while people with superior optics
                    have
                    > not managed to do that. It would be nice to get the whole story on
                    > this, but I am not sure we ever will.
                    >
                    > Steve
                    >
                    > --- In ccd-newastro@yahoogroups.com, "Randy Nulman" <rj.nulman@v...>
                    > wrote:
                    > > I saw the same thing when I got my 12.5 RC. The optics of my old
                    > C11
                    > > were relatively good, but my fwhm improved by almost 25% with the
                    > RC!
                    > > (This was comparing "on axis" stars for both scopes)
                    > >
                    > > I was originally expecting only an "off axis" improvement, but the
                    > > quality of the optics in the RCOS really made a difference.
                    > >
                    > > Randy Nulman
                    > >
                    > > --- In ccd-newastro@yahoogroups.com, "Wodaski Yahoo account"
                    > > <yahoo@w...> wrote:
                    > > > It has been my experience, both visually and with CCD, that poor
                    > > optics are
                    > > > more affected by seeing that good optics.
                    > > >
                    > > > An interesting case in point: On a night of exceptional seeing
                    at
                    > > New Mexico
                    > > > Skies, I took an image of M51 with the C14 and ST-10 binned 2x2
                    > > that was
                    > > > very good. Still a little soft, however. In the first tests of
                    > the
                    > > new 20"
                    > > > RC, on a night that was so bad I didn't bother to image with the
                    > > C14, the
                    > > > images of M51 were as good as they were on that best night with
                    > the
                    > > C14 -
                    > > > despite the fact that we are still making adjustments to the RC
                    > and
                    > > it's
                    > > > mounting to improve performance. This fact just blew me away.
                    > > >
                    > > > Ron Wodaski
                    > > > author of The New CCD Astronomy
                    > > > http://www.newastro.com
                    > > >
                    > > >
                    > > > -----Original Message-----
                    > > > From: clearviewh [mailto:clearview@c...]
                    > > > Sent: Saturday, May 31, 2003 8:13 PM
                    > > > To: ccd-newastro@yahoogroups.com
                    > > > Subject: [ccd-newastro] Re: S/N ; F ratio ; and RC vs LX200
                    > > >
                    > > >
                    > > > To tell you the truth, I think a LOT of it is location.
                    Sometimes
                    > I
                    > > > whine about not having the money for a nice RC and Paramount
                    mount
                    > > > but I have spent plenty on the domed observatory. Thing is, I
                    > wonder
                    > > > if I would get full value out of that kind of setup here. When
                    > > seeing
                    > > > is good, which is not that often, I get images that I am very
                    > proud
                    > > > of. The rest of the time, as I watch the guide star jumping
                    around
                    > > > from poor seeing, I wonder just how well even a Paramount would
                    > > > perform here.....at least that's what I keep telling myself....
                    > LOL
                    > > > Ed
                    > > >
                    > > > --- In ccd-newastro@yahoogroups.com, "Mark de Regt"
                    <deregt@e...>
                    > > > wrote:
                    > > > > Ed,
                    > > > >
                    > > > > This is something I have thought a lot about, and talked with
                    > > > people with
                    > > > > experience with both SCTs and RCs. I believe, of course, that
                    > the
                    > > > RC optics
                    > > > > are better than my LX200, but I also believet that my LX200
                    has
                    > > > excellent
                    > > > > optics. When you talk about the RC images you see, it is
                    worth
                    > > > keeping in
                    > > > > mind that people with RCs tend to be experienced imagers, and
                    > > often
                    > > > have
                    > > > > superior locations. Taking nothing away from Adam Block at
                    Kitt
                    > > > Peak (whose
                    > > > > images have become routinely sublime, they are so wonderful),
                    > and
                    > > > others, it
                    > > > > is also worth remembering that their scopes are bigger than
                    > most
                    > > of
                    > > > ours.
                    > > > > Most of the RCs you see are 12.5 inch, with some at 14.5 inch,
                    > 16
                    > > > inch, and
                    > > > > Adam now uses a 20 inch. I know that emulsion photographers
                    say
                    > > > that focal
                    > > > > ratio is the sole determiner of exposure length, but, with CCD
                    > > > imaging of
                    > > > > the heavens, I don't believe it--The larger the aperture, the
                    > less
                    > > > time it
                    > > > > takes to get good S/N, I think. Add to that the superior
                    > location
                    > > > someone
                    > > > > like Adam has--no light pollution and 7000 foot elevation, and
                    > you
                    > > > can't
                    > > > > even compare that circumstance to what most of us deal with.
                    > Add
                    > > > to that
                    > > > > the fact the many of the best imagers manage to get several
                    > images
                    > > > a month
                    > > > > (at least), year round, while I'm happy if I get ten in a
                    year;
                    > > the
                    > > > > experience in image acquisition and image processing, and its
                    > > > contribution
                    > > > > to the final result, should not be underestimated,
                    > > > >
                    > > > > I think that the optics themselves plays a pretty minor role
                    in
                    > > > what you see
                    > > > > with exposure length; the steadier mount is more important,
                    but
                    > > the
                    > > > AO-7
                    > > > > makes up for most of that. I believe that dark skies,
                    > elevation,
                    > > > and larger
                    > > > > aperture has a lot more to do with it than RC quality.
                    > > > >
                    > > > >
                    > > > >
                    > > > > > -----Original Message-----
                    > > > > > From: clearviewh [mailto:clearview@c...]
                    > > > > > Sent: Saturday, May 31, 2003 6:00 PM
                    > > > > > To: ccd-newastro@yahoogroups.com
                    > > > > > Subject: [ccd-newastro] S/N ; F ratio ; and RC vs LX200
                    > > > > >
                    > > > > >
                    > > > > > Just wanted to take this opportunity, while Ron is
                    apparently
                    > > > gone,
                    > > > > > to comment on the question of S/N only being related to F.R.
                    > I
                    > > > have
                    > > > > > known for a long time, that with my LX200, I have to take
                    MUCH
                    > > > longer
                    > > > > > exposure times than someone with say an RC on a Paramount
                    > with
                    > > the
                    > > > > > same FL and diameter. I have gone round and round on the
                    > subject
                    > > > and
                    > > > > > finally deceided that the QUALITY of the setup ALSO plays a
                    > role
                    > > > in
                    > > > > > S/N. Perhaps not, I agree, in the ACTUAL S/N, but a better
                    > setup
                    > > > > > spreads the signal around less, giving a better image. I
                    have
                    > to
                    > > > take
                    > > > > > a much longer exposures cause the poorer tracking, and
                    > optics,
                    > > of
                    > > > my
                    > > > > > LX200, spreads my signal out more..... bloated
                    > stars.....etc.
                    > > So
                    > > > > > when say a Rob Gendler with his 12 in RC at F9 takes a
                    > L:R:G:B
                    > > of
                    > > > > > 120:40:60:60, I have to take a 180:60:90:90 to get an image
                    > that
                    > > > > > appears to have a similar S/N even at F5....Comments??
                    > > > > > Ed
                    > > > > >
                    > > > > >
                    > > > > >
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