Video
A short film from 1927-1929, including footage of Krakatau eruptions, the Dutch Volcanological Survey base camp, and researchers monitoring the volcano.
Vladimir Petrushevsky can be seen at the end of the video [24:20], looking through binoculars as the smoke from burning leaves (presumably to keep away mosquitoes) wafts past the camera.
https://www.youtube.com/watch?v=4VYUZL1Kun8&feature=youtu.be
Source: Eyang Sastro, https://www.youtube.com/watch?v=4VYUZL1Kun8&feature=youtu.be