Contents - Index

Unguided Operation

Automatic dithering is provided for unguided operation along with an option to periodically realign the telescope to the desired target coordinates.



Dithering
Dithering is a process whereby the guide star location on the guider chip is moved between image exposures in either a random or  optimized manner.  When the guider control repositions the guide star to the new location, the image will be slightly displaced on the imager chip.  When the resultant images are aligned and properly combined, hot and cold pixels, cosmic ray hits and other sensor-specific artifacts are removed, much better than any hot/cold pixel routine can ever hope to achieve.  The resultant image is smoother and artifact-free.  See this link for more details on this technique.
Dithering can be done either totally randomly, as determined by a random number generator, or in a controlled manner to maximize separation between each sub-exposures artifacts while minimizing the overall guide star movement.  Both options are provided.  The amount of the dither is user-definable.  Here is a discussion on how to set the amount of dithering.
  • Dither method: Select Enhanced (preferred) or Random.
  • Maximum Dither: This is the peak dither value and can go +/- from the starting direction.  As an example, suppose Enhanced Dithering is selected with a Max Dither of 3 arc-sec.  The first sub-exposure will leave the guide star position undisturbed.  The second will move the X position of the guide star + 3 arc-sec.  The third will move the X position of the guide star - 3 arc-sec. from the first exposure.  Thus the total movement between the second and third exposure is 6 pixels but the movement relative to the first sub-exposure is ± 3 arc-sec.

    Periodic Realignment
    When a long series of unguided exposures are taken, the mount will gradually track off the target.  By using this feature, the telescope is periodically realigned to the target coordinates.  (If any periodic focusing using SkyStar is implemented, target realignment will occur during that process.  If that is used, additional periodic realignment will occur only as long as the time between SkyStar focus runs has exceeded the realignment period.
  • Realign scope every x minutes: If 0 is entered, this function is disabled.  If a non-zero value is entered, the telescope will be realigned to the target coordinates via a precision slew after the current exposure completes and after the specified interval has elapsed.