CCDciel is free software released under the terms of the
GNU General Public License
You can load a reference image of the object you want to capture to adjust the position of the telescope and the rotation of the camera. This is very useful to continue a sequence over many night.
You can adjust the display threshold and the color of the reference image in the preview options.
Normally you want the threshold to display only the stars from the reference image.
To load the image use the menu File / Open reference image
Then start a preview loop, it show the new image over the reference.
You can now move the telescope or rotate the camera to match the reference.
When you are satisfied with the result you can remove the reference image from the menu File / Clear reference image
To help to center the telescope open first the reference image with File / Open FITS file. Right click on the image and select “Resolve and slew to image center”. After the telescope stop slewing process as above to adjust the rotation.