Quote by: fitz
The 'exptime' parameter refers to the exposure time of the image, i.e. the value read from the 'exptime' keyword in the image header or if that can't be found, then the response you give when prompted for a value for the image. So there isn't just one value, it is the value for each image.
If the exposure time is stored in a different keyword then you can use the HEDIT task to add an EXPTIME keyword with the value. For example:
cl\$this->_split2($m[0]) hedit *.fits EXPTIME '(otime)' add+ ver-
would add a new EXPTIME keyword to every image using the value stored in the OTIME keyword.