Just an update....
I think the faster frame rate may be solvable - using the horizontal ROI (1930 x 100) definitely seems to be capable of >400 fps. (Note: a vertical ROI doesn't seem to have the same improvement - only achieving +/- 100 fps)
But getting a workable exposure to match is a bit more problematic.
With single frames from a 8 bit AVI the density range (full well) is 0 -256 ADU.
With the local continuum over exposed (>256) the core of the Ha is only registering at 70 ADU.
Fred Veio made a nice illustration in his book "The Spectrohelioscope" which shows the depth of exposure needed for the various Ha features - it also gives an indication of the intensity variation which can be achieved...
A profile of the Ha line shows the issue.
I'll do further testing with various exposures at the higher frame rate.
If things improve I'll move onto the nodding mirror option to give scans of 4 secs.
