Thank you very much Nasos, Akira, Ian, Tom, Armando and Jacques
Nasos, correct, 48 exposures of 30 seconds each. D750 with 15-30mm f2.8 Tamron lens at 15mm, f2.8 and ISO100 (with exposure lifted significantly as it got darker). I feel this is the biggest advantage of "ISO invariance": you don't have to adjust exposure during a process like this, risking disaster if you get it wrong. Keep in mind that there are no gaps, so you can't see the exposure.
There is also a bit of a memory associated with that range of photos (sorry for the waffle): The Blutkuppe are situated inside a national park where no off-road driving is allowed. And the specific tree was situated about 200m from the nearest road. In order not to ruin the shots, I sat in the dark, admiring the stars. However, as the night grew dark, my imagination kicked in. This was a national park, and although a dry area, we had seen some animals (Zebra and Kudu), and where they are present, that most adaptable of predators, the Leopard, often lurks too. And after a while, I actually heard a sound behind me. Like lightning I jumped up, whipped up my torch and switched on the light. About 5 yards behind me was a Bat-eared Fox, a beautiful little animal. Fortunately, although they are foxes, they eat virtually only insects, so it did not pose me a danger, but I promise my heart was racing!
That is why this star trail is only 48 images long. The light did ruin the 49th exposure, and I had lost my courage...
Tom, Zanzibar appears to be a beautiful destination, but do be careful. Africa can cause an obsession.
