Alexandra - I DO tend to trust Firecapture - for some things anyway
When I did my ISS capture a few weeks ago, I did exactly the same calculation of number of frames showing the ISS divided by transit time and compared the answer to what was reported by Firecapture. Like you, I found the numbers to agree perfectly - I got a much slower 26fps with the Grasshopper but 13 frames captured during a 0.55s transit were enough to get me smiling too
Its a pity you can't get FC v2.7 working as I find it to be a significant improvement. I had no problems getting it working with the Grasshopper ( it just auto-detected the camera and worked ) or my new ASI290MM. I have read of others having issues with v2.7 and ASI cameras and the suggestion that the problem is using an old version of the ASI SDK - v2.7 apparently needs the new version whereas v2.6 doesn't? If this wasn't part of the 'fixes' from Torsten then it might be worth a try? Others seem to have solved the problem by using the ASCOM drivers but all of my ASI cameras (120MM, 185MC and 290MM) work perfectly with v2.7 and the latest (29th June 2020) ASI SDK (from
https://astronomy-imaging-camera.com/software-drivers) on two different laptops.
The other issue I have had on my old imaging computer is that despite running from a folder rather than being 'installed', Firecapture seems to write temporary stuff to various places on the HD which is not cleared when the programme closes unexpectedly. This sometimes means that a full re-boot is needed after, for example, a camera connection failure. If this isn't done then Firecapture often reports that the 'camera can't be started' or some other error. In the past I have spent many unhappy hours swearing at the laptop having connected/disconnected cameras and restarted Firecapture several times to no avail. Eventually in desparation I switched the laptop off...... only to find that everything worked perfectly once it was switched on again.
Unless you have done so recently, it might be worth downloading v2.7 again as I understand some changes to SDKs etc have been made to solve other problems. Sorry if all of this is 'old hat' that you have already done - just trying to help
Don't you just love technology
