According to the book "Dream Palaces of Birmingham", Chris&Rosemary Clegg, the Capitol was designed by Arcibald Hurley Robijson and opened on the 4th April 1925. Four years later it was enlarged to a design by Satchwell&Roberts this increased the seating capacity to 1,400 from the previuos 900.
In 1979 the Cinema was tripled according to this book it closed for tripling on 23rd December and re opened on the 29th December, I find this difficult to believe. It re opened with the films "Bear Island" in the 450 seat screen 1, "Love at first Bite" in the 280 seat screen2 and"Bedknobs and Broomsticks" in the 130seat screen3.
The afore mentioned method of altering the aspect ratio of the screen, for Cinemascope presentation, by dropping a mask from the top of the screen was not unusual and was either done to save money or perhaps because it was not feasible to widen the proscenium arch. Cinemascope should have also come with four channel stereophonic sound, on a magnetic sound track, with speakers to the left,centre, and right with rear effects speakers making up the fourth channel, this was often not fitted to save costs. The anamorphic lenses needed to unsqueeze the image on the film were very expensive as well, so in order to try to get people back into the Cinema, after the introduction of TV, cost the industry quite a lot of cash.