Check readout times using hot pixels
You can check the accuracy of the readout times by the time stamp file.
Time Stamp File
In the Time Stamp File the times the program reads out a line are stored.
This should be exact enough for most circumstances. Only if you have doubts
in the function of the program, you may check it like that:
You can use one of the hot pixels on the CCD to check, if the intervals between
reading out the lines are equal.
If you take a drift scan image with closed shutter (dark frame), a hot pixel will
cause a "hot column". ( uncooled CCD)
(If you don't have a hot pixel on your CCD, you may use your telescope and an artificial star instead )
After the ramping, the values in that column should only change in the reach of
the readout noise.
If one line is read out to late, the value at the position of the hot pixel will
So you will get changes in the brightness of that hot column.
(The next line should be read earlier, so the value may decrease after that.)
There should be a correlation between the Time Stamp File and that hot column, but
regard the y position of the hot pixel.
There is a linear correlation between the readout time and the pixel values
in the hot column.
You may save that hot column as text file and load it to excel, to view it as diagram.
Here is an example, in this image some lines are read to late, because as a
second program was started, while an image was taken.
(While taking a drift scan image, do not touch the computer)
(The y axis indicates the pixel values, the x axis the y position )