Guiding Graphing

Discussion in 'Image Capture' started by David Holko, Mar 21, 2018.

  1. David Holko

    David Holko Cyanogen Customer

    Joined:
    Mar 13, 2018
    Messages:
    4
    Location:
    Port St Lucie (imaging from KPPSP)
    The last week of imaging , for the first two night the guiding was perfect, was flat lined. Then the guiding graph line started about one pixel below the center line and slowly move to two pixels, still straight but not on the center line. (x axis) the Y axis was still dead center and flat. Last couple of night were kinda the same way, the graphing lines either above or below the center line and flat. Just wondering why ?
     
  2. Doug

    Doug Staff Member

    Joined:
    Sep 25, 2014
    Messages:
    4,598
    Did you look at the guide star offset display while guiding? It's probably showing what the graph shows.

    First thought - it won't matter as long as it stays put.

    Second thought - this is a simple proportional control loop; it can't remove a constant offset. An example of a constant offset would be a constant drift. What could do that? Tracking rate of mount set incorrectly maybe? Or, more likely, drift due to offset polar alignment.
     
  3. David Holko

    David Holko Cyanogen Customer

    Joined:
    Mar 13, 2018
    Messages:
    4
    Location:
    Port St Lucie (imaging from KPPSP)
    Well, for me the mystery is that nothing was changed from the previous nights. Actually turning off guiding worked perfectly for the 5 minute subs that i was shooting. My polar alignment was set with Pole master, and near perfect. I will have to check this offset that you mention. I am fairly sure the mount was set using sidereal rate. I have two laptops I use, one is a backup, and the guiding graphs were the same on either computer. This was never observed all the previous times I was doing imaging but it is pretty common on one of my friend graphs, he is using a Mach One mount, same STi guide camera. I am just trying to get a understanding of this for both of us.
     
  4. Doug

    Doug Staff Member

    Joined:
    Sep 25, 2014
    Messages:
    4,598
    Polar alignment is never perfect, though if it's accurate then obviously drift is less likely. Also depending on which way the alignment is off, the drift rate and direction is strongly dependent on where in the sky you are pointed.

    Check what the X-Y offset display is showing; it should match the graph.
     
  5. David Holko

    David Holko Cyanogen Customer

    Joined:
    Mar 13, 2018
    Messages:
    4
    Location:
    Port St Lucie (imaging from KPPSP)
    Well, it will be something to investigate in the future.
     

Share This Page