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Re: Combining subs from different telescopes

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  • chasfranks71
    I would also think that the two telescopes will place the (Secondary spider) vane-generated stellar spikes at different angles on the stars. Might not be very
    Message 1 of 10 , Apr 19 4:10 AM
      I would also think that the two telescopes will place the (Secondary spider) vane-generated stellar spikes at different angles on the stars. Might not be very esthetic!
      Charles

      --- In ccd-newastro@yahoogroups.com, "Stan" <stan_ccd@...> wrote:
      >
      > P.S. Start by attempting to stack the already stacked masters from each scope. Try to weight them appropriately by accounting for aperture, total exp times, combine methods (sum or mean), camera gain, and resampling scale changes.
      >
      > That will at least tell you what you are up against. If that super-stack looks OK then you may be able to improve it further by going back to stack all of the individual exps (or it may be good enough to not bother).
      >
      > Stan
      >
    • mcgill.colin
      Dear Charles and Stan, Thank you both for your comments. I ve been thinking about this a little more. I think the correct thing is to try to work out the total
      Message 2 of 10 , Apr 28 3:28 AM
        Dear Charles and Stan,

        Thank you both for your comments. I've been thinking about this a little more.

        I think the correct thing is to try to work out the total number of photons observed/arcsec^2.

        So, if we have the individual stacks, we should weight them by:

        Gain*Nsubs/Pixarea

        The gain takes it from ADU to number of photons detected per sub, multiplying by the number of subs the total detected, and dividing by the pixel area the number per arcsecond.

        Differences in scope aperture, QE and subframe exposure time will all give rise to different number of counts in the average stacks, so will already have been accounted for.

        I also think we should try and align our cameras as well as we can to avoid multiple sets of spikes - good idea, Charles.

        Any other ideas?

        Thank you both,

        Colin

        --- In ccd-newastro@yahoogroups.com, "chasfranks71" <cfranks@...> wrote:
        >
        > I would also think that the two telescopes will place the (Secondary spider) vane-generated stellar spikes at different angles on the stars. Might not be very esthetic!
        > Charles
        >
        > --- In ccd-newastro@yahoogroups.com, "Stan" <stan_ccd@> wrote:
        > >
        > > P.S. Start by attempting to stack the already stacked masters from each scope. Try to weight them appropriately by accounting for aperture, total exp times, combine methods (sum or mean), camera gain, and resampling scale changes.
        > >
        > > That will at least tell you what you are up against. If that super-stack looks OK then you may be able to improve it further by going back to stack all of the individual exps (or it may be good enough to not bother).
        > >
        > > Stan
        > >
        >
      • Stan
        ... That applies for MEAN masters. If any of the masters are created via SUM then remove the Nsubs from the eq. This assumes that registration
        Message 3 of 10 , Apr 28 9:07 AM
          --- "mcgill.colin" <colin.mcgill@...> wrote:
          > I think the correct thing is to try to work out the
          > total number of photons observed/arcsec^2.
          > So, if we have the individual stacks, we should weight them by:
          >
          > Gain*Nsubs/Pixarea

          That applies for MEAN masters. If any of the masters are created via SUM then remove the Nsubs from the eq.

          This assumes that registration enlargement/reduction fails to preserve the flux. Some astro-programs have the option to preserve flux when resampling (e.g. CCDStack) Preserving flus normalizes effective gain by area, so:

          weight = Nsubs * Gain

          This weight does not account for asymmetric PSF. If some of the images are significantly sharper than others then it may be advantageous to over-weight them.

          This weight does not account for asymmetric S/N. For example it treats sky-limited and read-limited as equal but the S/N of a sky limited image is potentially superior. Similarly it is blind to variations in sky brightness. The equation could be expanded to account for these S/N issues but it would be somewhat unwieldy and probably wouldn't make that much difference. I suspect your biggest problems will be dealing with field distortions, PSF variations and flat errors.

          Stan
        • echesak@flash.net
          Sorry for the late reply here. I collaborate also, although with a similar scope and camera set-up. However, the best way that I ve found to combine images
          Message 4 of 10 , Apr 29 10:58 AM
            Sorry for the late reply here. I collaborate also, although with a similar scope and camera set-up. However, the best way that I've found to combine images is to use Registar. I use it to align images from different nights and from different scopes. It's simple and works flawlessly every time. I'd highly recommend it.

            I usually align stacks for each filter and them combine them in Photoshop.

            Eric

            --- In ccd-newastro@yahoogroups.com, "mcgill.colin" <colin.mcgill@...> wrote:
            >
            > Hi - I have just started collaborating with two other imagers.
            >
            > We have similar set ups, but not identical - two 8" RCs, one 10", all have different cameras.
            >
            > We've thought about combining all the individual (calibrated) frames, or just a weighted average of the integrated frames, but I'm sure there are other ways of doing this.
            >
            > Does anyone have any advice about the best way to combine data from different telescopes?
            >
            > Thank you,
            >
            > Colin
            >
          • Bob Runyan
            I am in total agreement regarding Registar. A great, very intuitive, simple to use program that does the job. I am not affiliated but a happy owner of this
            Message 5 of 10 , Apr 29 3:13 PM
              I am in total agreement regarding Registar. A great, very intuitive, simple
              to use program that does the job. I am not affiliated but a happy owner of
              this program.
              Bob R. http://rcfotos.selfip.net/Runyan


              -----Original Message-----
              From: ccd-newastro@yahoogroups.com [mailto:ccd-newastro@yahoogroups.com] On
              Behalf Of echesak@...
              Sent: Monday, April 29, 2013 12:58 PM
              To: ccd-newastro@yahoogroups.com
              Subject: [ccd-newastro] Re: Combining subs from different telescopes

              Sorry for the late reply here. I collaborate also, although with a similar
              scope and camera set-up. However, the best way that I've found to combine
              images is to use Registar. I use it to align images from different nights
              and from different scopes. It's simple and works flawlessly every time.
              I'd highly recommend it.

              I usually align stacks for each filter and them combine them in Photoshop.

              Eric

              --- In ccd-newastro@yahoogroups.com, "mcgill.colin" <colin.mcgill@...>
              wrote:
              >
              > Hi - I have just started collaborating with two other imagers.
              >
              > We have similar set ups, but not identical - two 8" RCs, one 10", all have
              different cameras.
              >
              > We've thought about combining all the individual (calibrated) frames, or
              just a weighted average of the integrated frames, but I'm sure there are
              other ways of doing this.
              >
              > Does anyone have any advice about the best way to combine data from
              different telescopes?
              >
              > Thank you,
              >
              > Colin
              >




              ------------------------------------
            • mcgill.colin
              Thank you all for your advice. Enclosed is the first fruit of our collaboration. The two others involved are Salvatore Iovene, who also runs Astrobin, and
              Message 6 of 10 , May 3, 2013
                Thank you all for your advice.

                Enclosed is the first fruit of our collaboration. The two others involved are Salvatore Iovene, who also runs Astrobin, and Samuel Diaz Lopez.

                This image is the result of about 12 hours of luminance data taken through a 10" GSO RC with an Atik 4000, combined with 7 hours of RGB data taken through an 8" Ikharos RC with an Atik 460ex.

                This image also benefited from final Pixinsight processing from Manuel Jimenez.

                http://astrob.in/40770/

                As a result, we all learned a great deal about our set ups, especially the flaws, not to mention the differences in out set ups. I hope our images will improve, but a pleasing start.

                Colin


                --- In ccd-newastro@yahoogroups.com, "Bob Runyan" <runrob@...> wrote:
                >
                > I am in total agreement regarding Registar. A great, very intuitive, simple
                > to use program that does the job. I am not affiliated but a happy owner of
                > this program.
                > Bob R. http://rcfotos.selfip.net/Runyan
                >
                >
                > -----Original Message-----
                > From: ccd-newastro@yahoogroups.com [mailto:ccd-newastro@yahoogroups.com] On
                > Behalf Of echesak@...
                > Sent: Monday, April 29, 2013 12:58 PM
                > To: ccd-newastro@yahoogroups.com
                > Subject: [ccd-newastro] Re: Combining subs from different telescopes
                >
                > Sorry for the late reply here. I collaborate also, although with a similar
                > scope and camera set-up. However, the best way that I've found to combine
                > images is to use Registar. I use it to align images from different nights
                > and from different scopes. It's simple and works flawlessly every time.
                > I'd highly recommend it.
                >
                > I usually align stacks for each filter and them combine them in Photoshop.
                >
                > Eric
                >
                > --- In ccd-newastro@yahoogroups.com, "mcgill.colin" <colin.mcgill@>
                > wrote:
                > >
                > > Hi - I have just started collaborating with two other imagers.
                > >
                > > We have similar set ups, but not identical - two 8" RCs, one 10", all have
                > different cameras.
                > >
                > > We've thought about combining all the individual (calibrated) frames, or
                > just a weighted average of the integrated frames, but I'm sure there are
                > other ways of doing this.
                > >
                > > Does anyone have any advice about the best way to combine data from
                > different telescopes?
                > >
                > > Thank you,
                > >
                > > Colin
                > >
                >
                >
                >
                >
                > ------------------------------------
                >
              • Ron Brant
                Nice photo Colin! Ron ... From: mcgill.colin To: ccd-newastro@yahoogroups.com Sent: Friday, May 03, 2013 5:36 AM Subject: [ccd-newastro] Re: Combining subs
                Message 7 of 10 , May 3, 2013
                  Nice photo Colin!
                  Ron
                  ----- Original Message -----
                  From: mcgill.colin
                  To: ccd-newastro@yahoogroups.com
                  Sent: Friday, May 03, 2013 5:36 AM
                  Subject: [ccd-newastro] Re: Combining subs from different telescopes



                  Thank you all for your advice.

                  Enclosed is the first fruit of our collaboration. The two others involved are Salvatore Iovene, who also runs Astrobin, and Samuel Diaz Lopez.

                  This image is the result of about 12 hours of luminance data taken through a 10" GSO RC with an Atik 4000, combined with 7 hours of RGB data taken through an 8" Ikharos RC with an Atik 460ex.

                  This image also benefited from final Pixinsight processing from Manuel Jimenez.

                  http://astrob.in/40770/

                  As a result, we all learned a great deal about our set ups, especially the flaws, not to mention the differences in out set ups. I hope our images will improve, but a pleasing start.

                  Colin

                  --- In ccd-newastro@yahoogroups.com, "Bob Runyan" <runrob@...> wrote:
                  >
                  > I am in total agreement regarding Registar. A great, very intuitive, simple
                  > to use program that does the job. I am not affiliated but a happy owner of
                  > this program.
                  > Bob R. http://rcfotos.selfip.net/Runyan
                  >
                  >
                  > -----Original Message-----
                  > From: ccd-newastro@yahoogroups.com [mailto:ccd-newastro@yahoogroups.com] On
                  > Behalf Of echesak@...
                  > Sent: Monday, April 29, 2013 12:58 PM
                  > To: ccd-newastro@yahoogroups.com
                  > Subject: [ccd-newastro] Re: Combining subs from different telescopes
                  >
                  > Sorry for the late reply here. I collaborate also, although with a similar
                  > scope and camera set-up. However, the best way that I've found to combine
                  > images is to use Registar. I use it to align images from different nights
                  > and from different scopes. It's simple and works flawlessly every time.
                  > I'd highly recommend it.
                  >
                  > I usually align stacks for each filter and them combine them in Photoshop.
                  >
                  > Eric
                  >
                  > --- In ccd-newastro@yahoogroups.com, "mcgill.colin" <colin.mcgill@>
                  > wrote:
                  > >
                  > > Hi - I have just started collaborating with two other imagers.
                  > >
                  > > We have similar set ups, but not identical - two 8" RCs, one 10", all have
                  > different cameras.
                  > >
                  > > We've thought about combining all the individual (calibrated) frames, or
                  > just a weighted average of the integrated frames, but I'm sure there are
                  > other ways of doing this.
                  > >
                  > > Does anyone have any advice about the best way to combine data from
                  > different telescopes?
                  > >
                  > > Thank you,
                  > >
                  > > Colin
                  > >
                  >
                  >
                  >
                  >
                  > ------------------------------------
                  >





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