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Re: Bob – Help! Was: moving pictures

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  • robertfields
    I have uploaded some subs onto the groups photos site under moving pics Essentially the subs move across the chip and as pointed out by Dennis I am losing
    Message 1 of 28 , Nov 30, 2009
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      I have uploaded some subs onto the groups photos site under "moving pics"
      Essentially the subs move across the chip and as pointed out by Dennis I am losing area once I get to stacking. Here is the link...I hope this works.

      http://groups.yahoo.com/group/sct-user/photos/album/1979505880/pic/list

      Bob

      --- In sct-user@yahoogroups.com, "dennis_persyk" <dpersyk@...> wrote:
      >
      > Hi Drew,
      >
      > Bob's complaint, if I may speak for him, was that he was losing image area due to the creep in RA and Dec from one frame to the next. I encounter the same thing when I take a two to four hour total exposure. Depending on where I am aimed in the sky, I can easily lose 5% of the total area due to rotation in four hours of imaging. Sure, virtually any aligning application will fix translation and rotation. But it can't reclaim the area lost due to overlapping subs.
      >
      > In my imaging setup http://dpersyk.home.att.net I encounter both flexural and rotational effects. Flexure occurs when I put the Canon 20D piggyback on the platform with a 300 mm zoom lens. The CG of the camera system is well ahead of the tiny area footprint of the tripod socket, and if I tap on the lens, I get large trailing along the axis of the tap. It is simply not a rigid setup.
      >
      > If I tap on the astrograph, there is no discernable motion. My pier is designed to withstand a 5 pound lateral push with less than 0.5 arc second deflection – see
      > http://home.att.net/~dpersyk/Pier_Design.htm
      > I have no flexural effects between the astrograph and the guide scope and the platform to the pier. But I have rotational effects that manifest themselves in long exposures.
      >
      > I don't have any software to aid me in polar aligning. I use the old fashioned drift method, which introduces refraction errors. I have a large orthogonality error – of the order of 20 arc minutes – that is evident when I do a meridian flip. Hence I can't easily make use of the flipping techniques that my goto mount (AP1200GTO) affords to those with small orthogonality errors. I haven't drift aligned in over five years, so maybe I need to spend a few hours drifting some full moon night.
      >
      > Clear skies,
      >
      > Dennis Persyk
      > Igloo (Now Roll-Off) Observatory Home Page http://dpersyk.home.att.net
      > Hampshire, IL
      >
      >
      > --- In sct-user@yahoogroups.com, "ancient.sull" <ancient.sull@> wrote:
      > >
      > > I'm still confused as to whether you are having star elongation in a single sub (which is one sort of problem, likely flexure) or a rotation comparing one sub to the next (which can be fixed with stacking software).
      > >
      > > Are the single subs of good quality?
      > >
      > > Drew S.
      > >
      >
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