It's likely they used various lenses over the years, and also different cameras and formats. Both started with 9x12 German plate cameras. It's said they used a 10x8 camera for many years, but it's more likely they shot 18x24 as 10x8 film wasn't available in Germany, the post WWII film holders for both sizes are have the same. I have a pair of new Fidelity 18x24 DDS new in their original box.
If you look at their images it's apparent they used different lenses, one shot of a Gas holder is obviously made with a wide angle lens, while others are made with a normal or slightly longer lens. Usually they used height to lessen the effects of a wide angle lens big tripods and step ladders.
Do a google search and you'll see they used 3 diffrent format cameras 9x12/5x4, 13x18/7x5 and 18x24/10x8, so while a rigidity in subject matter and composition, a fluidity in what cameras and lenses they used to achieve this.
Ian