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RE: [ccd-newastro] Re: New image M3

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  • Wodaski Yahoo account
    Short, 5-second exposures are going to be dominated by read noise from the camera. You would want to take the longest exposures you could before saturation
    Message 1 of 11 , Mar 31, 2003
      Short, 5-second exposures are going to be dominated by read noise from the
      camera. You would want to take the longest exposures you could before
      saturation occurs. For the ST-9E, that's going to be pretty close to 65,000.
      experiment to determine how long of an exposure you can take without
      saturation/blooming; it will vary for every camera/scope/sky/subject
      combination. See pages 435-6 to learn how to calculate saturation for your
      camera, and how to determine your dynamic range. Ideally, an exposure will
      occupy as much dynamic range as possible. The more signal you have in the
      image, the less effect various types of noise will have on the quality of
      the image.

      Basically, until the core actually saturates, you are almost certainly
      better off increasing the exposure duration. Are you familiar with how to
      use the black and white points of the image to make sure you are looking at
      the full range of data? The automatic contrast settings in most programs
      could easily fool you into thinking you are saturated when you are not, if
      you don't know about adjusting the black and white points. The bulk of
      chapter 8 covers this subject, and if you haven't read that yet, it should
      take you a long way toward understanding.

      Regarding a question in another email about non-linear histogram processing,
      see pages 381 and following for details.

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


      -----Original Message-----
      From: Elliott Brooks [mailto:ebrooks@...]
      Sent: Monday, March 31, 2003 11:28 PM
      To: ccd-newastro@yahoogroups.com
      Subject: [ccd-newastro] Re: New image M3


      Hi Larry,

      I do have an excellent mount. It's a Lichtenknecker Optics M100B I
      picked up in Belgium (I live in the south of Holland). So I could
      have autoguided, but I used a lot of short exposures because I
      thought at 30 or 45 sec the core would be too burned out. Already at
      5 sec the core is pretty bright. What do you think?

      Thanks,
      Elliott

      --- In ccd-newastro@yahoogroups.com, "laurenc319" <laurenc319@a...>
      wrote:
      > --- In ccd-newastro@yahoogroups.com, "Elliott Brooks"
      <ebrooks@t...>
      > wrote:
      > > Hello Group,
      > >
      > > On the main folder of the Files, I posted an image of M3. This
      is
      > > one of my first images, made on 13 March 2003. It is 60 stacked
      > > images of 5 sec each, unguided, with a C8 at f/10, using an ST-
      9XE.
      > > There was a half-moon, just past the meridian, seeing was good,
      not
      > > great. The outside temp was about 8deg C. I cooled the ST-9 to -
      > > 25deg C.
      > >
      > > In CCDSoft, I first set the background and range of each
      exposure.
      > > Then I adjusted brightness and contrast. Then I aligned and Add
      > > combined. In Photoshop, I adjusted the histo 3 times, then
      curves 3
      > > times as described in Ron's book, Ch 8 and 9. Then I applied an
      > > unsharp mask of 50%, radius 1.5 pixels, and threshold 0.
      > >
      > > The image is better after all the processing, but I have a
      feeling
      > > it could be better. Especially the core. Also the stars around
      the
      > > core seem to be all about the same brightness, etc. Those are my
      > > comments, but I welcome anyone elses input.
      > >
      > > Thanks,
      > > Elliott Brooks
      >
      >
      > Hi Elliot,
      >
      > I can say without doubt that your image is better than the first
      > image of m3 that I took.
      >
      > A couple of simple processing tricks to bring out the
      core ...after
      > stacking the images use ddp or a log stretch to bring it out and
      then
      > go on to photoshop.
      >
      > I'm puzzeled why you used such short exposures ( 5 sec ), longer
      > exposures are possible even unguided. I don't know what kind of
      mount
      > you have, but exposures of 30 or 60 seconds should be feasable
      with
      > good polar alignment. Then processing is much less of a chore with
      > only 6 images to stack.
      >
      > Keep shooting the stars...it's a great hobby,
      >
      >
      > clear skies,
      >
      > Larry Citro



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    • Randy Nulman
      Hi Elliott, The data is there in the core...it just needs some processing to bring it out. (longer exposures would have been helpful..you would get more data
      Message 2 of 11 , Apr 1, 2003
        Hi Elliott,
        The data is there in the core...it just needs some processing to
        bring it out. (longer exposures would have been helpful..you would
        get more data and overcome the read noise), but this image should be
        good enough for you to experiment with various processing techniques.

        A non linear stretch is when you brighten up (or darken) the brighter
        areas of an image separately from the fainter areas of the image.
        For example, you could tone down the bright core of the cluster or
        galaxy, yet at the same time you could separately brighten the
        fainter "outer areas" (such as dim spiral arms of a galaxy)

        DDP does this automatically for you and allows some control over the
        process (including sharpening)...I don't believe CCDSoft offers DDP
        and I'm not aware of any freeware that does. However, you can
        accomplish the same thing (with more precision) using "curves" in
        Photoshop. Ron's book has a whole chapter devoted on how to do this.
        Try reading the chapter, then play with your image and see what you
        can get between using curves and some unsharp sharpening of the image.

        Also note that many imagers will use several software programs since
        each has it's strong points. Maxim is very good at color combining
        as well as offering DDP. Personally, I also use it for image
        acquisition and guiding..but that's just a personal
        preference...CCDSoft is also very good for acquiring images.

        Hope this helps,
        Randy Nulman

        --- In ccd-newastro@yahoogroups.com, "Elliott Brooks" <ebrooks@t...>
        wrote:
        > Thanks Randy,
        >
        > Your image is what I'm aiming for. My question is, is it there if I
        > just play around with the data enough, or is the data just not
        there
        > and no amount of playing will get it out?
        >
        > I have CCDSoft and Photoshop, not Maxim, so I don't have DDP. Is
        > there an equivalent in either of the other two? What is the non-
        > linear stretch you mention and how do I do it?
        >
        > Thanks,
        > Elliott
        >
        > --- In ccd-newastro@yahoogroups.com, "Randy Nulman"
        <rj.nulman@v...>
        > wrote:
        > > Hi Elliott,
        > > Nice first attempt! Regarding the core, expert use of curves in
        > > photoshop can bring out the detail in the core as well as the
        > > extended stars of the globular. (Ron has an excellent version of
        > M13
        > > on the Homepage of ccdnewastro...you need to go into yahoo
        > directly
        > > to look at it (or maybe he'll chime in and provide a link.)
        > >
        > > Personally, I don't have Ron's skills and I cheat by using DDP in
        > > Maxim. This works pretty good, but lacks the control that you
        > would
        > > have if you did this in photoshop) Here's a link to an image I
        > did
        > > almost 3 years ago using DDP on M13 (This was also one of
        > my "first"
        > > images...so not very good but will give you an idea of how a good
        > non
        > > linear stretch will bring out core detail):
        > > http://www.nulman.darkhorizons.org/m13_lrgb.htm
        > >
        > > The original data looked similar to yours before the DDP.
        > >
        > > My only other comment is that the background looks very dark, and
        > you
        > > may have clipped low end data (thus losing some of the faint
        stuff
        > on
        > > the periphery) Clipping low end data is (unfortunately) easy to
        > do
        > > during processing...you need to keep checking the histogram to
        > make
        > > sure this doesn't happen. (Even now, I often screw up and have
        to
        > > undo things or start over when I make a mistake)
        > >
        > > If you work more with this image in either of the above mentioned
        > > ways, I think you'll be pleasantly surprised at the results!
        > >
        > > Again, great start..keep them coming,
        > > Randy Nulman
        > >
        > >
        > > --- In ccd-newastro@yahoogroups.com, "Elliott Brooks"
        > <ebrooks@t...>
        > > wrote:
        > > > Hello Group,
        > > >
        > > > On the main folder of the Files, I posted an image of M3. This
        > is
        > > > one of my first images, made on 13 March 2003. It is 60 stacked
        > > > images of 5 sec each, unguided, with a C8 at f/10, using an ST-
        > 9XE.
        > > > There was a half-moon, just past the meridian, seeing was good,
        > not
        > > > great. The outside temp was about 8deg C. I cooled the ST-9 to -
        > > > 25deg C.
        > > >
        > > > In CCDSoft, I first set the background and range of each
        > exposure.
        > > > Then I adjusted brightness and contrast. Then I aligned and Add
        > > > combined. In Photoshop, I adjusted the histo 3 times, then
        > curves 3
        > > > times as described in Ron's book, Ch 8 and 9. Then I applied an
        > > > unsharp mask of 50%, radius 1.5 pixels, and threshold 0.
        > > >
        > > > The image is better after all the processing, but I have a
        > feeling
        > > > it could be better. Especially the core. Also the stars around
        > the
        > > > core seem to be all about the same brightness, etc. Those are
        my
        > > > comments, but I welcome anyone elses input.
        > > >
        > > > Thanks,
        > > > Elliott Brooks
      • Elliott Brooks
        Thanks Ron, Basically without getting too technical (although I see I still have to do that, so I ll continue in the book), as I was taking the images and
        Message 3 of 11 , Apr 2, 2003
          Thanks Ron,

          Basically without getting too technical (although I see I still have
          to do that, so I'll continue in the book), as I was taking the
          images and looking at them, I thought the core was already pretty
          burned out at 5 sec. I thought for sure if I expose longer,
          especially for say 45 sec, I would really overburn the core to
          death. That's why I stayed at 5 sec. Can you say that 45 sec would
          have been better, ie not overburn when I thought I was already
          burning the core? Or should I just really overburn and then process
          the core later? (I hope I'm making myself clear here. I guess it's
          cause I'm new and not used to what processing can and can't do.)

          Thanks,
          Elliott


          --- In ccd-newastro@yahoogroups.com, "Wodaski Yahoo account"
          <yahoo@w...> wrote:
          > Short, 5-second exposures are going to be dominated by read noise
          from the
          > camera. You would want to take the longest exposures you could
          before
          > saturation occurs. For the ST-9E, that's going to be pretty close
          to 65,000.
          > experiment to determine how long of an exposure you can take
          without
          > saturation/blooming; it will vary for every
          camera/scope/sky/subject
          > combination. See pages 435-6 to learn how to calculate saturation
          for your
          > camera, and how to determine your dynamic range. Ideally, an
          exposure will
          > occupy as much dynamic range as possible. The more signal you have
          in the
          > image, the less effect various types of noise will have on the
          quality of
          > the image.
          >
          > Basically, until the core actually saturates, you are almost
          certainly
          > better off increasing the exposure duration. Are you familiar with
          how to
          > use the black and white points of the image to make sure you are
          looking at
          > the full range of data? The automatic contrast settings in most
          programs
          > could easily fool you into thinking you are saturated when you are
          not, if
          > you don't know about adjusting the black and white points. The
          bulk of
          > chapter 8 covers this subject, and if you haven't read that yet,
          it should
          > take you a long way toward understanding.
          >
          > Regarding a question in another email about non-linear histogram
          processing,
          > see pages 381 and following for details.
          >
          > Ron Wodaski
          > author of The New CCD Astronomy
          > http://www.newastro.com
          >
          >
          > -----Original Message-----
          > From: Elliott Brooks [mailto:ebrooks@t...]
          > Sent: Monday, March 31, 2003 11:28 PM
          > To: ccd-newastro@yahoogroups.com
          > Subject: [ccd-newastro] Re: New image M3
          >
          >
          > Hi Larry,
          >
          > I do have an excellent mount. It's a Lichtenknecker Optics M100B I
          > picked up in Belgium (I live in the south of Holland). So I could
          > have autoguided, but I used a lot of short exposures because I
          > thought at 30 or 45 sec the core would be too burned out. Already
          at
          > 5 sec the core is pretty bright. What do you think?
          >
          > Thanks,
          > Elliott
          >
          > --- In ccd-newastro@yahoogroups.com, "laurenc319" <laurenc319@a...>
          > wrote:
          > > --- In ccd-newastro@yahoogroups.com, "Elliott Brooks"
          > <ebrooks@t...>
          > > wrote:
          > > > Hello Group,
          > > >
          > > > On the main folder of the Files, I posted an image of M3. This
          > is
          > > > one of my first images, made on 13 March 2003. It is 60 stacked
          > > > images of 5 sec each, unguided, with a C8 at f/10, using an ST-
          > 9XE.
          > > > There was a half-moon, just past the meridian, seeing was good,
          > not
          > > > great. The outside temp was about 8deg C. I cooled the ST-9
          to -
          > > > 25deg C.
          > > >
          > > > In CCDSoft, I first set the background and range of each
          > exposure.
          > > > Then I adjusted brightness and contrast. Then I aligned and Add
          > > > combined. In Photoshop, I adjusted the histo 3 times, then
          > curves 3
          > > > times as described in Ron's book, Ch 8 and 9. Then I applied an
          > > > unsharp mask of 50%, radius 1.5 pixels, and threshold 0.
          > > >
          > > > The image is better after all the processing, but I have a
          > feeling
          > > > it could be better. Especially the core. Also the stars around
          > the
          > > > core seem to be all about the same brightness, etc. Those are
          my
          > > > comments, but I welcome anyone elses input.
          > > >
          > > > Thanks,
          > > > Elliott Brooks
          > >
          > >
          > > Hi Elliot,
          > >
          > > I can say without doubt that your image is better than the first
          > > image of m3 that I took.
          > >
          > > A couple of simple processing tricks to bring out the
          > core ...after
          > > stacking the images use ddp or a log stretch to bring it out and
          > then
          > > go on to photoshop.
          > >
          > > I'm puzzeled why you used such short exposures ( 5 sec ), longer
          > > exposures are possible even unguided. I don't know what kind of
          > mount
          > > you have, but exposures of 30 or 60 seconds should be feasable
          > with
          > > good polar alignment. Then processing is much less of a chore
          with
          > > only 6 images to stack.
          > >
          > > Keep shooting the stars...it's a great hobby,
          > >
          > >
          > > clear skies,
          > >
          > > Larry Citro
          >
          >
          >
          > 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/
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