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RE: Softwaremount

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  • bob_franke
    Hello Luis, I suggest you try working with what you already have. The Gemini has built-in routines for polar alignment and building a pointing model. I started
    Message 1 of 6 , Sep 28 12:10 AM
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      Hello Luis,

      I suggest you try working with what you already have. The Gemini has built-in routines for polar alignment and building a pointing model. I started with the same set up and got good results by using the Gemini routines. In my case, the scope, at f/6.3, was permanently mounted on the G11, with the Losmandy tripod. I had good pointing for over two years and only had to occasionally re-sync the pointing model.

      Regards,
      Bob
      Http://bf-astro.com
       



      ---In ccd-newastro@yahoogroups.com, <yahoo@...> wrote:

      The situation is not that simple. What is, in astronomy?

      First, having used both, I vastly prefer polar alignment by software to drift aligning. I think this comes down to a personal preference item; I suggest folks try to both to see which is easier and faster for them. 

      Loss of alignment can happen in many ways. A common one that is overlooked with medium and larger mounts is stress release: when you move larger parts, they tend to bind, and over time (especially diurnal heat cycling) that gets released, and the mount winds up somewhere else. (A large, soft mallet to the base of the pier can help, but sometimes the best answer is to re-align a week later.)

      And frost heaving is not the only way a pier can shift.

      Ron Wodaski



      On Sep 12, 2013, at 2:49 AM, phils67 <plsherman@...> wrote:

       

      I don't understand your need for polar alignment software. If you're pier mounted, removing and reinstalling a scope shouldn't effect polar alignment. If you need to release axis locks to mount the scope, then you might need to rebuild your pointing model but there are alternatives you can use.

      If you glue a small mirror to your mount, at the scope attach point, you can mount a laser pointer on a wall and mark where the reflection hits the wall. You can use this to reposition your mount to a known location after removing and reinstalling the scope. This should allow you to save and restore your pointing model.

      Polar alignment can be easily done using the drift method. I suspect, from your need to get it very accurate, that you're imaging which means that you can do your drift alignment using your camera which is a relatively quick process. Once you have the mount polar aligned, only an earthquake or ground heaving from freezing should effect the polar laignment.

      Phil


    • lbarneo2003
      Thanks Ron, Bob and Phil If I choose the polar alignment by software, as the FOV of my optic system (Celestron11/f6,3 with ST-402ME) is small (5.6 x 8.4
      Message 2 of 6 , Oct 7, 2013
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        Thanks Ron, Bob and Phil

        If I choose the polar alignment by software, as the FOV of my optic system (Celestron11/f6,3  with ST-402ME) is small (5.6 x 8.4 arcmin), I suppose that I can use my Nikon D5000 instead of ST-402ME with a FOV of 21 x 31.5 arcmin (in this case with f10 of the OTA) for the alignment, and then replace the Nikon with the ST-402 to capture the images. The weight of both cameras is similar. Is it correct?

        Luis



        ---In ccd-newastro@yahoogroups.com, <bfranke@...> wrote:

        Hello Luis,

        I suggest you try working with what you already have. The Gemini has built-in routines for polar alignment and building a pointing model. I started with the same set up and got good results by using the Gemini routines. In my case, the scope, at f/6.3, was permanently mounted on the G11, with the Losmandy tripod. I had good pointing for over two years and only had to occasionally re-sync the pointing model.

        Regards,
        Bob
        Http://bf-astro.com
         



        ---In ccd-newastro@yahoogroups.com, <yahoo@...> wrote:

        The situation is not that simple. What is, in astronomy?

        First, having used both, I vastly prefer polar alignment by software to drift aligning. I think this comes down to a personal preference item; I suggest folks try to both to see which is easier and faster for them. 

        Loss of alignment can happen in many ways. A common one that is overlooked with medium and larger mounts is stress release: when you move larger parts, they tend to bind, and over time (especially diurnal heat cycling) that gets released, and the mount winds up somewhere else. (A large, soft mallet to the base of the pier can help, but sometimes the best answer is to re-align a week later.)

        And frost heaving is not the only way a pier can shift.

        Ron Wodaski



        On Sep 12, 2013, at 2:49 AM, phils67 <plsherman@...> wrote:

         

        I don't understand your need for polar alignment software. If you're pier mounted, removing and reinstalling a scope shouldn't effect polar alignment. If you need to release axis locks to mount the scope, then you might need to rebuild your pointing model but there are alternatives you can use.

        If you glue a small mirror to your mount, at the scope attach point, you can mount a laser pointer on a wall and mark where the reflection hits the wall. You can use this to reposition your mount to a known location after removing and reinstalling the scope. This should allow you to save and restore your pointing model.

        Polar alignment can be easily done using the drift method. I suspect, from your need to get it very accurate, that you're imaging which means that you can do your drift alignment using your camera which is a relatively quick process. Once you have the mount polar aligned, only an earthquake or ground heaving from freezing should effect the polar laignment.

        Phil


      • phils67
        The size of your FOV has almost no effect on using a camera for polar alignment. Of course, your can always swap cameras as you stated but that s a lot of
        Message 3 of 6 , Oct 11, 2013
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          The size of your FOV has almost no effect on using a camera for polar alignment. Of course, your can always swap cameras as you stated but that's a lot of work.

          Drift alignment using a camera is done using the same aiming points that you'd use for a visual drift alignment. I use a 70 second exposure with 5 seconds tracked, 30 seconds slewing E then 35 seconds slewing W. Slew rate should be 1x sidereal. The E slew stops the mount from moving while the W slew moves it a bit past the starting point.

          Your image will show a point for the 5 second tracked portion of the image with two trails making a V shape. You adjust the mount until the V collapses into a line that passes through the center of the star formed by the tracked portion of the image. You can double the sensitivity of the test by using slews of 60 and 65 seconds. The beauty of this technique is that it doesn't matter if the star drifts off the chip during the slews because you're only interested in the area where the return trail passes through the star at the start of the image.

          You should be able to see a single pixel error in the return trail from the W slew. Your image scale per pixel will give you the absolute error in arc seconds.

          Phil
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