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Re: aligning narrowband images

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  • CurtisC
    Sorry, I left off part of my post. Thank you for your help and advice :)
    Message 1 of 11 , Jul 31, 2011
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      Sorry, I left off part of my post. Thank you for your help and advice :)

      --- In ccd-newastro@yahoogroups.com, Ron Wodaski <yahoo@...> wrote:
      >
      > 20-minute exposures is good, but they could always be longer for any narrow-band image. <g> You do have a fast scope, so I would expect reasonable results from those exposures.
      >
      > Imaging with the moon up is always fraught with risk. Depending on how the off-axis illumination from the moon plays out - perversely, it can be worse at a position that is further away, it all depends on the light path inside the scope - you could definitely have gotten bright spots in some of your images that do not flat out. The moon reflects all of the colors of the sun, which is rich in most of the emission bands, so reflections off the moon _might_ be a hazard in variable ways. From the information you've provided, I would expect that the moon is possibly the source of the unwanted color in your final image. I suspect that your images are not really flat because of either the off-axis light, or sky gradients.
      >
      > Ron Wodaski
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      >
      > On Jul 31, 2011, at 2:01 AM, CurtisC wrote:
      >
      > > Sorry -- total of 9 hrs of data: 9 x 20 min in each NB color, unbinned. I didn't shoot any luminance or clear-filter frames.
      > >
      > > --- In ccd-newastro@yahoogroups.com, Ron Wodaski <yahoo@> wrote:
      > >>
      > >> Let's start with some basics. What is the focal ratio of that scope? What camera are you using? How long are your exposures? Is there any light pollution in that area of the sky where you are? (Ha does a good job blocking light pollution, but OIII and SII are susceptible to it.)
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      > >> Ron Wodaski
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      > >> On Jul 30, 2011, at 11:30 PM, CurtisC wrote:
      > >>
      > >>> I may not even be asking the question properly, or I may not correctly understand what I've been reading. I'm getting into narrowband imaging (Ha, OIII, SII). The North America Nebula practically fell together as a Hubble palette image, and I was able to achieve a spectacular result that got lots of "likes" and compliments. M16 has been a lot -- a lot!! -- more difficult. Apparently the fact that it's 3x farther than the N.A. and possibly 1/9 as bright is probably part of my problem. What I'm reading about narrowband says I should align the images (not just the subs within each color) before working on them in Photoshop. The question: can CCDStack save each image as though it were aligned with a base image (say, the H-alpha) without having to actually combine them? For some reason, people seem to be cool to the idea of using auto-align in PS. I wouldn't use it for the subs, but it seems to work well enough for aligning the three colors. In addition, everything I do with
      > > M16
      > >>> leaves me with lots of green in the outer parts of the nebula. I was just looking at a narrowband image of M16 by Russell Croman, and it was almost enough to make me want to put all of my equipment on Astromart. Of course, he did it with a 20-inch scope vs. my 4-inch, but even in the central part that he shows, I haven't been able to get close to what he has.
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