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M42 in Near IR, [SII] and Halpha

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  • Richard Crisp (SBC)
    this is a project I ve been meaning to start for some time. It is a widefield using Near IR longpass, [SII] and Halpha the bright stars in the Trapezium really
    Message 1 of 37 , Feb 1, 2005
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      this is a project I've been meaning to start for some time. It is a widefield using Near IR longpass, [SII] and Halpha

      the bright stars in the Trapezium really severely limited my exposure time in Near IR, otherwise the sensor would bloom terribly. I ended up taking 15 second exposures. I had to take 100 of those subexposures to get 25 minutes total exposure.

      the Halpha and [SII] data were 25 exposures of 60 seconds each.

      each exposure with this camera, IMG6303, is 12.3MB. So I had a lot of raw data to crunch: 150 exposures of 12.3MB each.

      Even so, the data is a bit grainy so I may shoot more data another night soon. Who'd have thought that 150 exposures would be too few?

      http://www.narrowbandimaging.com/m42_ap180_6303_NirS2Ha_page.htm

      it takes about one minute to cycle through a 15 second exposure roughly, just as a data point.



      [Non-text portions of this message have been removed]
    • rdcrisp
      ... are ... I think the signal does build up, slowly. i forgot the equation but I believe the signal adds in an rms fashion. and the noise adds too but there
      Message 37 of 37 , Feb 1, 2005
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        --- In ccd-newastro@yahoogroups.com, "Rick Wiggins"
        <rickwiggins@e...> wrote:
        >
        > Richard,
        > There are no wrongs here (other than I have not won the Lottery
        > yet!). I do think my proposed theory is correct. Idon't think you
        are
        > gaining much after 10 to 20 exposures to average down the noise. As
        > far as building up the signal, I don't think that happens. Signals
        > that are so weak as to vary sow up on one frame and not another are
        > probably interpreted as noise. Signals that do show up in all


        I think the signal does build up, slowly.

        i forgot the equation but I believe the signal adds in an rms
        fashion. and the noise adds too but there is a net win in SNR as you
        take more data from what i remember last time stan went through this

        i need to look at my references a bit and get back.

        no question that the 100 frame data is better than 20 of them. I
        already looked at that.



        frames
        > but vary, will be recognized as signal and will be improved. Try
        > using the technique that I suggested if you have time. That's the
        > same as some use for LRBG of M42. They shoot 10 secs, 5 mins,etc.
        > They use the sweet spot out of each set with layers and masks. This
        > should work for you as well. I just don't think that super high
        > numbers of frames buys you much in this situation. I hope that Stan
        > or one of the SNR Gurus chimes in on this one.
        > Tonight I will be continuing on my light box project.
        > Thanks, Rick
        >
        > --- In ccd-newastro@yahoogroups.com, "rdcrisp" <rdcrisp@s...> wrote:
        > >
        > >
        > > here is why i did what i did, right or wrong
        > >
        > > i wanted to image the m42 object without blooming the trapezium
        > stars
        > > and using my nir longpass filter.
        > >
        > > i could expose for about 15 seconds without blooming too badly.
        > that
        > > is it. so my maxiumum exposure time was limited to 15 seconds.
        > >
        > > with 15 seconds my ability to capture the faint nebulosity is
        > > challenged to say the least. so to get as much as I could i
        decided
        > > to take a lot of exposures in hopes that the faint signal would
        > > accumulate.
        > >
        > > this is a situation where low read noise is nice because in 15
        > > seconds there is a part of the nebula where the accumulated
        signal
        > is
        > > just above the noise floor set by the read noise. so the lower
        the
        > > read noise, the better I capture the faint nebulosity.
        > >
        > > So while the maximum exposure time was limited by avoiding
        > blooming,
        > > the faint nebulosity detection/capture was limited by the noise
        > floor
        > > of the camera and the read noise is the biggest part of that as I
        > > understand.
        > >
        > > That was the "why" that I did what I did, right or wrong.
        > >
        > > still the image is noiser than I'd like. I may fiddle with it
        again
        > > tonight.
        > >
        > > rdc
        > >
        > >
        > >
        > > --- In ccd-newastro@yahoogroups.com, "Rick Wiggins"
        > > <rickwiggins@e...> wrote:
        > > >
        > > > Richard,
        > > > The shot is very interesting and quite well done. I am curious
        > > about
        > > > the "100" frames. I have seen this done by several others as
        > well.
        > > I
        > > > must be missing something. ROn and Stan please chime in if you
        > > > agree/disagree/or can shed some light on my thoery here. The
        > basic
        > > > exposure of 15 secs captures all the signal for the bright
        > portions
        > > > of the frame (probably near 50% saturation levels in the
        > brightest
        > > > sections). The series of exposures does not increase the signal
        > of
        > > > the bright areas, but serves to randomize the noise allowing
        for
        > > > reduction of noise in an averaged (or similarly processed)
        > combined
        > > > image. The combination of the captured signal and
        > reduced/averaged
        > > > noise gives higher SNR and a higher quality image. So, after
        you
        > > have
        > > > captured enough images to drive down noise (probably 10-20),
        the
        > > > subsequent frames don't buy you much; they do reduce noise, but
        > > only
        > > > marginally so. Wouldn't it be better to take 10 more frames at
        > > longer
        > > > exposures; say 10 at 1 minute, and 10 at 10 minutes, and then
        > > > composite these combined frames to use each combination's best
        > SNR
        > > > areas of the frame? If the blooming would kill you, then I
        > > understand
        > > > why you wouldn't do this with this camera; but if that's the
        > case,
        > > > what about using a ABG camera to take the long exposures for
        the
        > > > dimmer sections and then combine. It just seems to me that
        after
        > 20
        > > > frames or so, there is marginal (and probably invisible to our
        > eye)
        > > > improvement. Is there something else going on when stacking
        > images,
        > > I
        > > > mean other then noise averaging?
        > > > Thanks for listening to my thoeries.
        > > > Rick
        > > > --- In ccd-newastro@yahoogroups.com, "Richard Crisp \(SBC\)"
        > > > <rdcrisp@s...> wrote:
        > > > > this is a project I've been meaning to start for some time.
        It
        > is
        > > a
        > > > widefield using Near IR longpass, [SII] and Halpha
        > > > >
        > > > > the bright stars in the Trapezium really severely limited my
        > > > exposure time in Near IR, otherwise the sensor would bloom
        > > terribly.
        > > > I ended up taking 15 second exposures. I had to take 100 of
        those
        > > > subexposures to get 25 minutes total exposure.
        > > > >
        > > > > the Halpha and [SII] data were 25 exposures of 60 seconds
        each.
        > > > >
        > > > > each exposure with this camera, IMG6303, is 12.3MB. So I had
        a
        > > lot
        > > > of raw data to crunch: 150 exposures of 12.3MB each.
        > > > >
        > > > > Even so, the data is a bit grainy so I may shoot more data
        > > another
        > > > night soon. Who'd have thought that 150 exposures would be too
        > few?
        > > > >
        > > > >
        http://www.narrowbandimaging.com/m42_ap180_6303_NirS2Ha_page.htm
        > > > >
        > > > > it takes about one minute to cycle through a 15 second
        exposure
        > > > roughly, just as a data point.
        > > > >
        > > > >
        > > > >
        > > > > [Non-text portions of this message have been removed]
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