Charon and drift scan images taken by WinScan

Charon is a program written by Bill J. Gray see: Charon(extern link)

To use Charon to examine drift scan images,
fill in the settings in Charon like this:

Report file name


Saturation point


Cutoff point


Focal len (inches)


Image offset


Pix width (microns)


Scale tolerance
(large images 0.1)


Pix height(microns)


Search distance
(large images about 4.0 )


SBIG file format: Image is uninverted
FITS: Image is inverted

Observer code


Match to GSC-ACT

Time offset


File date gives end of exposure

Maximum residual
(large images 2.0)


Mag limit:


Number stars used



White stars on black

Object name:

GSC 1267 237

RA/dec in decimal seconds

Simple centroiding

Video mode:

320 x 200

Max tilt angle:

90.00 +/- 4.00

Linear (first-order) fit

Photometric band:

Centroid size


Save settings

Charon will calculate a correct mid exposure time for drift scan images .
( but only outside the ramping )
In images in SBIG file format, a line:
Note = Sekunden je Reihe 0.17810216469252
should be present
or start Charon with the argument -d
To use drift scanned FITS files, start Charon always with the argument -d
To start Charon with the argument -d, first start Charon without arguments and fill in the settings, and then start Charon with the argument -d, you may add arguments for the image file and for the object like:
C:\GuideDN\ -ogsc 1895 575 -d
The time and date in the file info of an image taken by WinScan, will indicate the time, when the first line of the image is read out. Therefore in Charon it is necessary to set: File date gives end of exposure
In files sliced from JimsSilce or ViewScan the time in the file info is also the time, the first line (of the new file) is read out, same settings as mentioned before.
When using FITS files you must fill in the focal len and the pixel size in Charon in the settings, using SBIG files, these values are taken from the file header.
It is also important to set:
Images SBIG file format: Image is uninverted
Images FITS file format: Image is inverted
Max tilt angle: 90.00 +/- 4.00
(Max tilt angle: 90.00 +/- 1.00 should also work)
(In images taken by WinScan West is at the top)
In large images,it should be set:
Maximum residual 2.0
Search distance 2 or 4 or more, depends on the size of the image

If Charon don't works with that settings, try to change some items
It may be easier to use smaller or sliced images
(I got Charon work with images up to 765 * 10000 pixels, but the settings in Charon have to be adjusted very carefully)

In large images, it may help, to fill in the exact RA and DEC of the center of the image (at Object name)(ViewScan can calculate the center of an image).
Video mode: try different settings