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RE: [ccd-newastro] Uploaded new images

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  • Ron Wodaski
    Heh, heh -- theory may not be correct about this area. My T-shirt flats were taken at .11 second, the shortest that the ST-8E will allow. perhaps
    Message 1 of 8 , Sep 30, 2000
      Heh, heh -- theory may not be correct about this area. <g>

      My "T-shirt flats" were taken at .11 second, the shortest that the ST-8E
      will allow. perhaps averaging is what does it, but these are far and away
      the best, most well-matched flats I've ever taken. And I've taken hundreds
      of flats in search of the perfect flat, so this is no small thing.

      I took a picture of the setup, and will have documentation up on the book
      site, hopefully by tomorrow afternoon (Sunday).

      Ron Wodaski
      The New Astronomy Book Site - http://www.newastro.com



      -----Original Message-----
      From: Michael Clary [mailto:tricomp1@...]
      Sent: Saturday, September 30, 2000 4:06 PM
      To: ccd-newastro@egroups.com
      Subject: Re: [ccd-newastro] Uploaded new images


      Hi Ron,

      Interested in your "T-Shirt Flat" and look forward to your comments. One
      quick question. You mentioned exposures of "very short duration" and this
      would obviously depend on the thickness of the cloth material as well as the
      illumination intensity. I would guess you're talking about something in the
      1-5 second range (perhaps less). In my limited experience and from talking
      to others, it seems that "very short duration" exposures run the risk of
      unevenness resulting from the opening and closing of the shutter in a short
      period. Perhaps median combining for a master flat would overcome this
      obstacle. My obvious question is: at what exposure duration were you doing
      your testing?

      Thanks,
      Michael Clary
      tricomp1@...


      on 9/30/00 3:45 PM, Ron Wodaski at ronw@... wrote:

      > The best method I've found for flat fielding isn't in that chapter; I
      > discovered it just two days ago. <g> I'll be adding it shortly.
      >
      > ....You then take a
      > daylight images with a very short duration, maybe 4-6 of them, average
      them,
      > and you have a superb flat field.



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    • KSBTK@HOME
      Good Morning Ron: An interesting discovery! I am almost afraid to ask how you came up with this method . I presume the t-shirt should be white. Is that
      Message 2 of 8 , Oct 1 5:00 AM
        Good Morning Ron:

        An interesting discovery! I am almost afraid to ask how you came up with
        this method <g>.

        I presume the t-shirt should be white. Is that correct? Also, can the
        images be taken any time of the day or is toward evening better?

        I will give this a try with the fastar set-up and a dew shield. I'll place
        the image in the files section for your evaluation.

        Clear skies,
        Kevin
        ksbtk@...



        > The best method I've found for flat fielding isn't in that chapter; I
        > discovered it just two days ago. <g> I'll be adding it shortly.
        >
        > I'm not sure, though that it will work with the Fastar. The method
        involves
        > placing a t-shirt over the front of the scope. With a conventional setup,
        > you can simply stretch the t-shirt across the opening. You then take a
        > daylight images with a very short duration, maybe 4-6 of them, average
        them,
        > and you have a superb flat field.
        >
        > It's worth a try with the faster setup, but the problem may be that the
        > shirt can't be easily stretched flat because of the camera sticking out.
        If
        > you have a dew shield, it would be worth a try, but if you don't use the
        dew
        > shield when imaging, it might give you a flat that won't be quite right.
        > This would have to be tested to find out.
        >
        > Otherwise, I would think that a twilight flat or a dome flat would be most
        > effective with the Fastar setup.
      • Ron Wodaski
        Yes, a white t-shirt. I have no idea how or why I thought it up; it just seemed like it was worth trying. I really can evaluate the image on its own; what
        Message 3 of 8 , Oct 1 9:28 AM
          Yes, a white t-shirt. I have no idea how or why I thought it up; it just
          seemed like it was worth trying.

          I really can' evaluate the image on its own; what determines its value is
          how well it works as a flat field on your images.

          Ron Wodaski
          The New Astronomy Book Site - http://www.newastro.com



          -----Original Message-----
          From: KSBTK@HOME [mailto:ksbtk@...]
          Sent: Sunday, October 01, 2000 5:00 AM
          To: ccd-newastro@egroups.com
          Subject: Re: [ccd-newastro] Uploaded new images


          Good Morning Ron:

          An interesting discovery! I am almost afraid to ask how you came up with
          this method <g>.

          I presume the t-shirt should be white. Is that correct? Also, can the
          images be taken any time of the day or is toward evening better?

          I will give this a try with the fastar set-up and a dew shield. I'll place
          the image in the files section for your evaluation.

          Clear skies,
          Kevin
          ksbtk@...



          > The best method I've found for flat fielding isn't in that chapter; I
          > discovered it just two days ago. <g> I'll be adding it shortly.
          >
          > I'm not sure, though that it will work with the Fastar. The method
          involves
          > placing a t-shirt over the front of the scope. With a conventional setup,
          > you can simply stretch the t-shirt across the opening. You then take a
          > daylight images with a very short duration, maybe 4-6 of them, average
          them,
          > and you have a superb flat field.
          >
          > It's worth a try with the faster setup, but the problem may be that the
          > shirt can't be easily stretched flat because of the camera sticking out.
          If
          > you have a dew shield, it would be worth a try, but if you don't use the
          dew
          > shield when imaging, it might give you a flat that won't be quite right.
          > This would have to be tested to find out.
          >
          > Otherwise, I would think that a twilight flat or a dome flat would be most
          > effective with the Fastar setup.





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