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Data combinations from different nights

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  • BillyPatt
    As I try to gather data that spans multiple nights, I am of course faced with different seeing conditions from night to night. How much difference matters?
    Message 1 of 7 , Jul 26, 2006
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      As I try to gather data that spans multiple nights, I am of course
      faced with different seeing conditions from night to night. How much
      difference matters? If I have a good night with an average FWHM of
      say 2.5 on one night and mediorce seeing another night with a FWHM of
      4.0, would i combine that data or wait for a clearer night? Is there
      a break point in data quality where you have chosen to dump the
      inferior data? I'd love to hear what experiences others might have
      had with this issue.

      Thanks in advance,

      Bill Patterson
    • Adam Block
      Hi Bill, I have always chosen to add everything together. You will still get the benefit of an increase in S/N. However, perhaps the best way to do it is to
      Message 2 of 7 , Jul 26, 2006
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        Hi Bill,

        I have always chosen to add everything together. You will still get the benefit of
        an increase in S/N. However, perhaps the best way to do it is to weight the exposures
        according to "quality." Some programs will permit this kind of condition at the point of
        combining the data.

        But with regards to pretty pictures- a bright colorful image beats a noisier though more
        resolved image every time.

        Adam



        ------------------------------------------------------------

        Adam Block
        ngc1535@...
        http://caelumobservatory.com/
        Caelum videre iussit, et erectos ad sidera tollere vultus.
        He bid them look at the sky and lift their faces to the stars.
        --Ovid, Metamorphoses 1. 85-8
        ------------------------------------------------------------



        -----Original Message-----
        From: BillyPatt [mailto:bill@...]
        Sent: Wednesday, July 26, 2006 05:32 PM
        To: ccd-newastro@yahoogroups.com
        Subject: [ccd-newastro] Data combinations from different nights

        As I try to gather data that spans multiple nights, I am of course
        faced with different seeing conditions from night to night. How much
        difference matters? If I have a good night with an average FWHM of
        say 2.5 on one night and mediorce seeing another night with a FWHM of
        4.0, would i combine that data or wait for a clearer night? Is there
        a break point in data quality where you have chosen to dump the
        inferior data? I'd love to hear what experiences others might have
        had with this issue.

        Thanks in advance,

        Bill Patterson






        [Non-text portions of this message have been removed]
      • Adam Block
        Hi Bill, I have always chosen to add everything together. You will still get the benefit of an increase in S/N. However, perhaps the best way to do it is to
        Message 3 of 7 , Jul 26, 2006
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          Hi Bill,

          I have always chosen to add everything together. You will still get the benefit of
          an increase in S/N. However, perhaps the best way to do it is to weight the exposures
          according to "quality." Some programs will permit this kind of condition at the point of
          combining the data.

          But with regards to pretty pictures- a bright colorful image beats a noisier though more
          resolved image every time.

          Adam



          ------------------------------------------------------------

          Adam Block
          ngc1535@...
          http://caelumobservatory.com/
          Caelum videre iussit, et erectos ad sidera tollere vultus.
          He bid them look at the sky and lift their faces to the stars.
          --Ovid, Metamorphoses 1. 85-8
          ------------------------------------------------------------



          -----Original Message-----
          From: BillyPatt [mailto:bill@...]
          Sent: Wednesday, July 26, 2006 05:32 PM
          To: ccd-newastro@yahoogroups.com
          Subject: [ccd-newastro] Data combinations from different nights

          As I try to gather data that spans multiple nights, I am of course
          faced with different seeing conditions from night to night. How much
          difference matters? If I have a good night with an average FWHM of
          say 2.5 on one night and mediorce seeing another night with a FWHM of
          4.0, would i combine that data or wait for a clearer night? Is there
          a break point in data quality where you have chosen to dump the
          inferior data? I'd love to hear what experiences others might have
          had with this issue.

          Thanks in advance,

          Bill Patterson






          [Non-text portions of this message have been removed]
        • gary_teamgs
          Hey Bill, I personally don t worry much if the FWHM values are fairly different, provided I am imaging the RGB subs. For the L or Ha, I am a little more
          Message 4 of 7 , Jul 27, 2006
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            Hey Bill,
            I personally don't worry much if the FWHM values are fairly
            different, provided I am imaging the RGB subs. For the L or Ha, I am a
            little more critical. If I am imaging a more detailed subject like a
            galaxy, I will use CCDInspector and try to cull out the worst images.
            For larger more diffuse images like nebula, I may be more leniant. You
            can always try combining all of the images, then do a version being
            more selective, and subjectively evaluating if it makes a difference
            for the particular target.

            Regards,

            Gary

            --- In ccd-newastro@yahoogroups.com, "BillyPatt" <bill@...> wrote:
            >
            > As I try to gather data that spans multiple nights, I am of course
            > faced with different seeing conditions from night to night. How much
            > difference matters? If I have a good night with an average FWHM of
            > say 2.5 on one night and mediorce seeing another night with a FWHM of
            > 4.0, would i combine that data or wait for a clearer night? Is there
            > a break point in data quality where you have chosen to dump the
            > inferior data? I'd love to hear what experiences others might have
            > had with this issue.
            >
            > Thanks in advance,
            >
            > Bill Patterson
            >
          • BillyPatt
            Thanks Adam and Gary. I have the data for a good experiment. I have six hours of luminance from two nights of varying conditions. It may be interesting to
            Message 5 of 7 , Jul 27, 2006
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              Thanks Adam and Gary. I have the data for a good experiment. I
              have six hours of luminance from two nights of varying conditions.
              It may be interesting to try the image both ways.

              Bill

              --- In ccd-newastro@yahoogroups.com, "gary_teamgs" <gary_teamgs@...>
              wrote:
              >
              > Hey Bill,
              > I personally don't worry much if the FWHM values are fairly
              > different, provided I am imaging the RGB subs. For the L or Ha, I
              am a
              > little more critical. If I am imaging a more detailed subject
              like a
              > galaxy, I will use CCDInspector and try to cull out the worst
              images.
              > For larger more diffuse images like nebula, I may be more
              leniant. You
              > can always try combining all of the images, then do a version
              being
              > more selective, and subjectively evaluating if it makes a
              difference
              > for the particular target.
              >
              > Regards,
              >
              > Gary
              >
              > --- In ccd-newastro@yahoogroups.com, "BillyPatt" <bill@> wrote:
              > >
              > > As I try to gather data that spans multiple nights, I am of
              course
              > > faced with different seeing conditions from night to night. How
              much
              > > difference matters? If I have a good night with an average FWHM
              of
              > > say 2.5 on one night and mediorce seeing another night with a
              FWHM of
              > > 4.0, would i combine that data or wait for a clearer night? Is
              there
              > > a break point in data quality where you have chosen to dump the
              > > inferior data? I'd love to hear what experiences others might
              have
              > > had with this issue.
              > >
              > > Thanks in advance,
              > >
              > > Bill Patterson
              > >
              >
            • gary_teamgs
              Hey Bill, I just finished up 3 hours of Ha data from M20, and the FWHM was very poor all night, due to the altitude, the high temps, and some wind. They
              Message 6 of 7 , Jul 27, 2006
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                Hey Bill,
                I just finished up 3 hours of Ha data from M20, and the FWHM was
                very poor all night, due to the altitude, the high temps, and some
                wind. They increased from 4 to 6 by the end of the exposures. I
                tried including all the images, as well as only keeping the best 90
                minutes, and, for this image on this night, while I can indeed see a
                slight increase in resolution with the 90 minute comibine, the 200
                minute version is much smoother, and I most likely will go with the
                latter. If I were imaging a galaxy, I might just decide to keep
                only the good images, and add more data from another night.

                Regards,

                Gary

                --- In ccd-newastro@yahoogroups.com, "BillyPatt" <bill@...> wrote:
                >
                > Thanks Adam and Gary. I have the data for a good experiment. I
                > have six hours of luminance from two nights of varying
                conditions.
                > It may be interesting to try the image both ways.
                >
                > Bill
                >
                > --- In ccd-newastro@yahoogroups.com, "gary_teamgs" <gary_teamgs@>
                > wrote:
                > >
                > > Hey Bill,
                > > I personally don't worry much if the FWHM values are fairly
                > > different, provided I am imaging the RGB subs. For the L or Ha,
                I
                > am a
                > > little more critical. If I am imaging a more detailed subject
                > like a
                > > galaxy, I will use CCDInspector and try to cull out the worst
                > images.
                > > For larger more diffuse images like nebula, I may be more
                > leniant. You
                > > can always try combining all of the images, then do a version
                > being
                > > more selective, and subjectively evaluating if it makes a
                > difference
                > > for the particular target.
                > >
                > > Regards,
                > >
                > > Gary
                > >
                > > --- In ccd-newastro@yahoogroups.com, "BillyPatt" <bill@> wrote:
                > > >
                > > > As I try to gather data that spans multiple nights, I am of
                > course
                > > > faced with different seeing conditions from night to night.
                How
                > much
                > > > difference matters? If I have a good night with an average
                FWHM
                > of
                > > > say 2.5 on one night and mediorce seeing another night with a
                > FWHM of
                > > > 4.0, would i combine that data or wait for a clearer night?
                Is
                > there
                > > > a break point in data quality where you have chosen to dump
                the
                > > > inferior data? I'd love to hear what experiences others might
                > have
                > > > had with this issue.
                > > >
                > > > Thanks in advance,
                > > >
                > > > Bill Patterson
                > > >
                > >
                >
              • Wodaski Yahoo
                Data from multiple nights is, after all, just data - no difference from having gathered it on a single night. Seeing can change from minute to minute, hour to
                Message 7 of 7 , Aug 1, 2006
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                  Data from multiple nights is, after all, just data - no difference from
                  having gathered it on a single night. Seeing can change from minute to
                  minute, hour to hour, and night to night.

                  The only way to find out how well the data comes together is to give it
                  a try. If I have a mixture of data quality, I will usually try a variety
                  of combinations to see if any one stands out as the best. I'll also try
                  different methods of combining.

                  If you really want to optimize your data rejection, then look into
                  CCDStack from CCDWare. It has more sophisticated data rejection
                  techniques than other programs.

                  Ron Wodaski

                  BillyPatt wrote:
                  > As I try to gather data that spans multiple nights, I am of course
                  > faced with different seeing conditions from night to night. How much
                  > difference matters? If I have a good night with an average FWHM of
                  > say 2.5 on one night and mediorce seeing another night with a FWHM of
                  > 4.0, would i combine that data or wait for a clearer night? Is there
                  > a break point in data quality where you have chosen to dump the
                  > inferior data? I'd love to hear what experiences others might have
                  > had with this issue.
                  >
                  > Thanks in advance,
                  >
                  > Bill Patterson
                  >
                  >
                  >
                  >
                  >
                  >
                  >
                  > Yahoo! Groups Links
                  >
                  >
                  >
                  >
                  >
                  >
                  >
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