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Re: New image M3

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  • 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 1 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
      >
      >
      >
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