With the sucess of those orders Thomas turned his attention to telescopes and mounts exclusively. He founded Grubbs of Dublin, a company specializing in large observatory instruments that provided telescopes to some of the world's largest observatories throughout the nineteenth and twentieth centuries.
His son, Howard, was born in 1844. With such great exposure to the astronomical world from both his father and a near neighbor, the third Earl of Rosse, Howard himself developed an interest in telescope building. Like his father he attended Trinity College, but left before graduating to help in the family business. He joined the company in 1865, three years before his father's retirement, and took charge of the business after Thomas' death in 1878. It was under Sir Howard's leadership that the business gained world wide recognition, building some of the nineteenth century's greatest telescopes, including the 48" Great Melbourne Telescope, the 27" refractor for Royal Observatory in Vienna, the largest refractor in the world at that time. It was the Vienna refractor that really established Howard's reputation. From that time on Grubb's recieved contracts from the world's greatest observatories, and Howard was knighted in 1887.
Grubb also supplied optical devices to the Allies during the first world war. The periscope had recently been invented, but had design flaws. Howard Grubb corrected the problems and came up with a device the military could use.
By 1925 Grubb's was in decline. Sir Howard was 81 and the company was nearly bankrupt, when Sir Charles Parsons took over and merged the two family businesses. Charles Parsons was the son of William Parsons, third Earl of Rosse and neighbor of Thomas Grubb who had built "Parson's Leviaathon," the 74" reflector that had been the world's largest telescope for seventy years. Grubb Parsons moved to Newscastle (England) and continued building large observatoy instruments until 1985, including the Radcliffe 74" inch reflector and the 1.9 meter William Herschel Telescope, the largest of the Isaac newton Group and the largest telescope in Western Europe.