Sorry learn of your uncle Michael's passing. There is quite a lot of information about Hugh Lyon Tennent online now. Here's an excerpt from a Tennent's Brewery brochure you might find interesting.
Hugh Lyon Tennent (1817-1874). Advocate. Born in Edinburgh in 1817, he was the younger son of Patrick Tennent (1782-1872), Writer to the Signet, and Margaret Rodger Lyon (1794-1867). He was the brother of another member of the Edinburgh Calotype Club, Robert Tennent. Hugh was a keen sailor and with other members of his family sailed around the Western Isles in 1838. An account of this cruise is held at the National Library of Scotland, (shelfmark Acc.12071). After qualifying as an advocate in 1840 he was appointed Sheriff-substitute of Lanarkshire at Airdrie in 1853 prior to a similar appointment at Greenock in 1856. The index to volume one of the Edinburgh Calotype Club albums is in Tennent's hand and he was possibly responsible for compiling the album itself. He was also a member of the Photographic Society of Scotland established in 1856. It is likely that Hugh Lyon Tennent took most of the photographs initialled T in volume 1. Hugh Tennent was something of a philanthropist. He promoted the work of the Discharged Prisoners Aid Society, he was also known as a connoisseur of fine art in Greenock. Tennent was part of the family involved with the Tennents brewery in Glasgow, but he spent a lot of his time in Fairlie, which features in many of the photographs. In 1855 Tennent married Agnes Halsey in London. He died in Edinburgh in 1874 and was buried there in the Dean Cemetery.
Also, the "Pencils of Light" exhibit is quite extraordinary, of which he was a key contributor. You'll find pictures of him and his family if you browse around a bit: http://digital.nls.uk/pencilsoflight/index.html
Lastly, a number of Ancestry.com family trees contain information about his ancestors and progeny. Just plug in "Hugh Lyon Tennent" although, FYI, there is more than one person by that name, e.g., he had a grandson of that name.