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RGB filter factors or different exposure times?

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  • allanberzins
    Hello, I ve been imaging with my mono 383L for over a year now after several years using a modified DSLR. With the mono work I have always combined RGB
    Message 1 of 8 , Jan 1, 2012
      Hello,
      I've been imaging with my mono 383L for over a year now after several years using a modified DSLR. With the mono work I have always combined RGB exposures using filter factors (new type Baader LRGB filters) determined by C2V star calibration. For me these factors work out to Red 0.62, Green 0.78 and Blue 1.0.

      I was looking at some subs recently and it is very clear that for equal exposure time (5 min) the red is very much brighter (mean ADU 15,162) than the green (6,968) and blue (3,404) which sort of fits with the overall C2V trend.

      Looking at the high noise level especially in the blue subs I was thinking it might be more beneficial rather than exposing all filters equally, to spend less time exposing red and longer in green and possibly even longer in blue hopefully improving the overall s/n in green and blue but taking a similar overall time.

      Any comments, what does anyone else do please?

      PS I've also posted this on the Atik group.
    • JoeMize
      Allen, try multiplying your exposure times by your G2V ratios to gather real data rather than compensating in Color Combine. That should help with noise.
      Message 2 of 8 , Jan 1, 2012
        Allen, try multiplying your exposure times by your G2V ratios to gather real
        data rather than compensating in Color Combine. That should help with
        noise. Also check your G2V ratios for several different G2V stars spread
        across the sky. HTH...joe :)


        "May You Go Among The Imperishable Stars"
        Joe Mize www.cav-sfo.com
        Chiefland Astronomy Village (CAV), Fla
        StarFields Observatory, (SFO).

        ----- Original Message -----
        From: "allanberzins" <allan.berzins@...>
        To: <ccd-newastro@yahoogroups.com>
        Sent: Sunday, January 01, 2012 8:25 AM
        Subject: [ccd-newastro] RGB filter factors or different exposure times?


        > Hello,
        > I've been imaging with my mono 383L for over a year now after several
        > years using a modified DSLR. With the mono work I have always combined RGB
        > exposures using filter factors (new type Baader LRGB filters) determined
        > by C2V star calibration. For me these factors work out to Red 0.62, Green
        > 0.78 and Blue 1.0.
        >
        > I was looking at some subs recently and it is very clear that for equal
        > exposure time (5 min) the red is very much brighter (mean ADU 15,162) than
        > the green (6,968) and blue (3,404) which sort of fits with the overall C2V
        > trend.
        >
        > Looking at the high noise level especially in the blue subs I was thinking
        > it might be more beneficial rather than exposing all filters equally, to
        > spend less time exposing red and longer in green and possibly even longer
        > in blue hopefully improving the overall s/n in green and blue but taking a
        > similar overall time.
        >
        > Any comments, what does anyone else do please?
        >
        > PS I've also posted this on the Atik group.
        >
        >
        >
        > ------------------------------------
        >
        >
        >
        >
        >
      • Stan
        ... There is little reason for equal time RGB exps unless the filter/camera ratios are close to 1:1:1 (or if you have no choice due to OSC/Bayer/DSLR).
        Message 3 of 8 , Jan 1, 2012
          --- "allanberzins" <allan.berzins@...> wrote:
          > ... thinking it might be more beneficial rather than exposing
          > all filters equally, to spend less time exposing red...

          There is little reason for equal time RGB exps unless the filter/camera ratios are close to 1:1:1 (or if you have no choice due to OSC/Bayer/DSLR). Otherwise the only reason for equal times that I can think of is convenience (e.g. all three can use the same dark master, though dark scaling/adaptation removes that reason).

          Apportioning exps times according to the filter ratios can result in a better S/N balance. But for an even truer S/N balance it is also necessary to compensate for sky, dark and read noises, though few (if any) imagers go that far. Just be sure to correctly compensate for the different exp times when applying your filter ratios to create the color-combine image.

          Stan
        • allanberzins
          Stan and Joe, thanks for your advice. I will definitely go the way of using exposure time to compensate for the lower blue and green sensitivity. Thanks Allan.
          Message 4 of 8 , Jan 3, 2012
            Stan and Joe, thanks for your advice.
            I will definitely go the way of using exposure time to compensate for the lower blue and green sensitivity.
            Thanks
            Allan.

            --- In ccd-newastro@yahoogroups.com, "Stan" <stan_ccd@...> wrote:
            >
            > --- "allanberzins" <allan.berzins@> wrote:
            > > ... thinking it might be more beneficial rather than exposing
            > > all filters equally, to spend less time exposing red...
            >
            > There is little reason for equal time RGB exps unless the filter/camera ratios are close to 1:1:1 (or if you have no choice due to OSC/Bayer/DSLR). Otherwise the only reason for equal times that I can think of is convenience (e.g. all three can use the same dark master, though dark scaling/adaptation removes that reason).
            >
            > Apportioning exps times according to the filter ratios can result in a better S/N balance. But for an even truer S/N balance it is also necessary to compensate for sky, dark and read noises, though few (if any) imagers go that far. Just be sure to correctly compensate for the different exp times when applying your filter ratios to create the color-combine image.
            >
            > Stan
            >
          • CurtisC
            Bring me up-to-date, Joe. How does one go about that?
            Message 5 of 8 , Jan 3, 2012
              Bring me up-to-date, Joe. How does one go about that?

              --- In ccd-newastro@yahoogroups.com, "JoeMize" <jmize@...> wrote:
              >
              > Allen, try multiplying your exposure times by your G2V ratios to gather real
              > data rather than compensating in Color Combine.
            • JoeMize
              Curtis, I determine my G2V values using D.Goldman s procedure. Then I multiply each filter s value by my chosen base exposure time for finding the G2V
              Message 6 of 8 , Jan 4, 2012
                Curtis, I determine my G2V values using D.Goldman's procedure. Then I multiply each filter's value by my chosen base exposure time for finding the G2V Compensated Exposure time.

                My 1994 AP155EDFS w/Field Flattener, STL11K w/AstroDon Gen-II G2V values are:
                1.05 - Red
                1.00 - Green
                1.13 - Blue

                Chosen Exposure time 600sec
                600sec X 1.05 = 630sec Red exposure.
                600sec X 1.00 = 600sec Green exposure.
                600sec X 1.13 = 678sec Blue exposure.

                I guess one could also do the same with eXcalibrator's values but I've never used it. Maybe someday. HTH...joe :)


                "May You Go Among The Imperishable Stars"
                Joe Mize www.cav-sfo.com
                Chiefland Astronomy Village (CAV), Fla
                StarFields Observatory, (SFO).

                ----- Original Message -----
                From: "CurtisC" <calypte@...>
                To: <ccd-newastro@yahoogroups.com>
                Sent: Tuesday, January 03, 2012 9:30 PM
                Subject: [ccd-newastro] Re: RGB filter factors or different exposure times?


                > Bring me up-to-date, Joe. How does one go about that?
                >
                > --- In ccd-newastro@yahoogroups.com, "JoeMize" <jmize@...> wrote:
                >>
                >> Allen, try multiplying your exposure times by your G2V ratios to gather real
                >> data rather than compensating in Color Combine.
                >
                >
                >
                > ------------------------------------
                >
                >
                >
                >
                >

                [Non-text portions of this message have been removed]
              • Mark Acker
                I believe another possibility here is to use CCD AutoPilot.  v5 can do this for you.  I have not gotten around to doing that yet, but will at some point.
                Message 7 of 8 , Jan 4, 2012
                  I believe another possibility here is to use CCD AutoPilot.  v5 can do this for you.  I have not gotten around to doing that yet, but will at some point.  It is a G2V calculation as well and simply automates the process.

                  Mark 


                  ________________________________
                  From: JoeMize <jmize@...>
                  To: ccd-newastro@yahoogroups.com
                  Sent: Wednesday, January 4, 2012 10:33 AM
                  Subject: Re: [ccd-newastro] Re: RGB filter factors or different exposure times?


                   
                  Curtis, I determine my G2V values using D.Goldman's procedure. Then I multiply each filter's value by my chosen base exposure time for finding the G2V Compensated Exposure time.

                  My 1994 AP155EDFS w/Field Flattener, STL11K w/AstroDon Gen-II G2V values are:
                  1.05 - Red
                  1.00 - Green
                  1.13 - Blue

                  Chosen Exposure time 600sec
                  600sec X 1.05 = 630sec Red exposure.
                  600sec X 1.00 = 600sec Green exposure.
                  600sec X 1.13 = 678sec Blue exposure.

                  I guess one could also do the same with eXcalibrator's values but I've never used it. Maybe someday. HTH...joe :)

                  "May You Go Among The Imperishable Stars"
                  Joe Mize www.cav-sfo.com
                  Chiefland Astronomy Village (CAV), Fla
                  StarFields Observatory, (SFO).

                  ----- Original Message -----
                  From: "CurtisC" <calypte@...>
                  To: <ccd-newastro@yahoogroups.com>
                  Sent: Tuesday, January 03, 2012 9:30 PM
                  Subject: [ccd-newastro] Re: RGB filter factors or different exposure times?

                  > Bring me up-to-date, Joe. How does one go about that?
                  >
                  > --- In ccd-newastro@yahoogroups.com, "JoeMize" <jmize@...> wrote:
                  >>
                  >> Allen, try multiplying your exposure times by your G2V ratios to gather real
                  >> data rather than compensating in Color Combine.
                  >
                  >
                  >
                  > ------------------------------------
                  >
                  >
                  >
                  >
                  >

                  [Non-text portions of this message have been removed]




                  [Non-text portions of this message have been removed]
                • Bob Franke
                  Hi Joe, If you don t have color balanced filters, it s best to first calibrate your image train with G2V stars. Then adjust the RGB exposure times or
                  Message 8 of 8 , Jan 4, 2012
                    Hi Joe,

                    If you don't have color balanced filters, it's best to first calibrate your image train with G2V stars. Then adjust the RGB exposure times or sub-frame counts per the calibration. As a last step, use eXcalibrator to tweak the color balance when creating the RGB image.

                    Your G2V calibration is similar to my eXcalibrator results. I also have an STL-11k with AstroDon Gen II filters and usually have to increase the blue by about 10 to 15%

                    Regards,
                    Bob
                    http://bf-astro.com/eXcalibrator/excalibrator.htm

                    --- In ccd-newastro@yahoogroups.com, "JoeMize" <jmize@...> wrote:
                    >
                    > Curtis, I determine my G2V values using D.Goldman's procedure. Then I multiply each filter's value by my chosen base exposure time for finding the G2V Compensated Exposure time.
                    >
                    > My 1994 AP155EDFS w/Field Flattener, STL11K w/AstroDon Gen-II G2V values are:
                    > 1.05 - Red
                    > 1.00 - Green
                    > 1.13 - Blue
                    >
                    > Chosen Exposure time 600sec
                    > 600sec X 1.05 = 630sec Red exposure.
                    > 600sec X 1.00 = 600sec Green exposure.
                    > 600sec X 1.13 = 678sec Blue exposure.
                    >
                    > I guess one could also do the same with eXcalibrator's values but I've never used it. Maybe someday. HTH...joe :)
                    >
                    >
                    > "May You Go Among The Imperishable Stars"
                    > Joe Mize www.cav-sfo.com
                    > Chiefland Astronomy Village (CAV), Fla
                    > StarFields Observatory, (SFO).
                    >
                    > ----- Original Message -----
                    > From: "CurtisC" <calypte@...>
                    > To: <ccd-newastro@yahoogroups.com>
                    > Sent: Tuesday, January 03, 2012 9:30 PM
                    > Subject: [ccd-newastro] Re: RGB filter factors or different exposure times?
                    >
                    >
                    > > Bring me up-to-date, Joe. How does one go about that?
                    > >
                    > > --- In ccd-newastro@yahoogroups.com, "JoeMize" <jmize@> wrote:
                    > >>
                    > >> Allen, try multiplying your exposure times by your G2V ratios to gather real
                    > >> data rather than compensating in Color Combine.
                    > >
                    > >
                    > >
                    > > ------------------------------------
                    > >
                    > >
                    > >
                    > >
                    > >
                    >
                    > [Non-text portions of this message have been removed]
                    >
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