Rosatom, the Russian state energy company, posted a documentary about the 1961 Tsar Bomba nuclear weapons test, the most powerful on record. The documentary (itself obviously of the era) contains footage that was previously unreleased, according to commentators. The 50-megaton action starts about 22m in.
This video purports to be a compilation of the freshly-declassified bits:
The mushroom cloud was about 67 km (42 mi) high (over seven times the height of Mount Everest), which meant that the cloud was above the stratosphere and well inside the mesosphere when it peaked. The cap of the mushroom cloud had a peak width of 95 km (59 mi) and its base was 40 km (25 mi) wide.
All buildings in the village of Severny (both wooden and brick), located 55 km (34 mi) from ground zero within the Sukhoy Nos test range, were destroyed. In districts hundreds of kilometres from ground zero, wooden houses were destroyed, stone ones lost their roofs, windows, and doors, and radio communications were interrupted for almost one hour. One participant in the test saw a bright flash through dark goggles and felt the effects of a thermal pulse even at a distance of 270 km (170 mi). The heat from the explosion could have caused third-degree burns 100 km (62 mi) away from ground zero. A shock wave was observed in the air at Dikson settlement 700 km (430 mi) away; windowpanes were partially broken for distances up to 900 kilometres (560 mi). Atmospheric focusing caused blast damage at even greater distances, breaking windows in Norway and Finland. Despite being detonated 4.2 kilometres (2.6 mi) above ground, its seismic body wave magnitude was estimated at 5.0–5.25
