Hi Gunter, looking at your HolyGrail-tutorial and want to try myself. I see you from the start of the sequence have an interval of 15 seconds, with a shutter time of 1/40, and later the shuttertime become longer. It is no problem to change the shuttertime in the interval, but how do you change the intervaltime on your camera when you are shooting, as i can see you have done here?
And is there a reason you have a very long intervaltime in the start (15 seconds) while a very short shuttertime? But i can see the result is very good.

Normally I keep the interval constant to avoid the sequence to speeding up.
But of course, technically you can ramp the interval too - you just need a controller that is able to do so. qDslrDashboard for example has an internal timer that is able to do interval ramping.