I was thinkig about real velocity of shutter curtain. I guess that vertial curtain velocity does not change and changes just timing of second curtain release. It means that slot between curtains travels at constant speed, but width of slot depends on shutter speed set up. The amount of light reaching the sensor is the same as shutter would have been fully opened for a very short time, e. g. 1/8000 s. Are my thoughts correct? If yes, how fast the curtain could travel?