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Re: [ccd-newastro] Re: WTG Don

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  • msandquist
    Thanks for all the information, I just need to use them for a while and see what happens. I also really need to get a robofocus to help me with the focus
    Message 1 of 7 , Jun 1, 2003
      Thanks for all the information, I just need to use them for a while and see
      what happens.
      I also really need to get a robofocus to help me with the focus issues.
      Hope your shots turned out good. I passed out at my computer at about 0230
      and had
      a 1.5hr nap.


      ----- Original Message -----
      From: Don Goldman <donclearview@...>
      To: <ccd-newastro@yahoogroups.com>
      Sent: Saturday, May 31, 2003 9:46 AM
      Subject: [ccd-newastro] Re: WTG Don

      > Hi, Mike,
      > The image is not going to move off the chip with the H-a filter on
      > the FSQ. It will likely have to be refocused due to the greater
      > thickness of the H-a filter compare to your LRGBs. The transmission
      > window ("bandpass") of the H-a filter will move to slightly shorter
      > wavelengths at f/5 compared to f/10. So, at f/10, the "window" may
      > be designed to be centered at 656.7 nm and transmitting 80% of the H-
      > a photons passing through. At f/5, the window may now be centered at
      > 655 nm and may only be transmitting 50% of the H-a photons that are
      > still at 656.7 nm. Take this to extremes and the "window" will move
      > far enough away that only a small % of the H-a photons will come
      > through. That may be the case for a FASTAR or HYPERSTAR system at
      > f/1.9. In all of the above, you should still see very little
      > difference in your stars since they emit broadband light that won't
      > be much different over these changes. I'm not quite sure what test
      > you did, but you may consider trying to shoot a bright H-a target
      > like the fringes around the Ring or Dumbbell so you can be sure the
      > object is there, and centered on the small TC237 CCD. If you are in
      > the middle of the Pelican or North American with no obvious feature
      > on that small chip, and out of focus, for example, you may not know
      > it????? I may have missed the point, but hey, I groggy (and happy)
      > from an all-night imaging session for the first time in months.
      > Let's see. Do I do the househould bills or process the images???? <g>
      > Don
      > www.astrodon.com
      > --- In ccd-newastro@yahoogroups.com, "msandquist" <msandquist@j...>
      > wrote:
      > > Hi Don,
      > > I remember the light show well...now by the time I reach Marysville
      > at
      > > night, I can see your dome already 25 deg. or
      > > so above the southern horizon. I am however impressed with the
      > images you
      > > have managed to capture under such
      > > bright conditions!
      > > What I was wondering about the FSQ/Ha was the incident angles at
      > wich the
      > > image reaches the chip (PixCell 237) and
      > > given the chips physical size, weather there are angles involved
      > that are
      > > accute enough to cause drift from the Ha line?
      > > I don't have any way to know if there is loss on a purely visual
      > evaluation.
      > > If I expose an evenly illuminated target using the 4.5nm filt.would
      > I just
      > > be generating a Ha Flat Field or would I be able to measure some
      > fall off
      > > and calculate drift drift from the 4.5nm line. I think some measure
      > of
      > > wavelength shift would
      > > be a better way.
      > > I just got the filters and haven't had time to do much in the way of
      > > imaging.
      > > Thanks for your input Don.
      > >
      > > Mike
      > >
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