This attractive little book, first published by the National Maritime Museum in Greenwich in 2009, has now been re-released in the US as well as the UK. After a brief discussion of astronomy before the telescope, Dunn moves us briskly from the invention of the telescope to the huge instruments of today, then briefly touches on other types of astronomy, such as radio astronomy, and what the future might hold.
As befits a book for the general reader, Dunn intersperses sections on both the non-astronomical adoption of telescopes--think, in particular, sailors--and on public reaction to astronomical discoveries. There are amusing as well as serious illustrations. The level of technical detail doesn't go much beyond the difference between a convex and a concave lens and the basic configurations of different telescopes. While my ideal book on telescopes would be far more technical, this book wasn't written for someone like me. This is the best book on the telescope for a general audience I've encountered.
I would like to add a little information on the invention of the telescope. Dunn notes that the idea of the telescope predates its putative inventor, Hans Lipperhey (Lippershey in some references). He suggests Lipperhey deserves credit for being the first to realize the "device's possibilities". I consider that unlikely. People wanted to make a telescope work because they knew it would be useful. Rolf Willach has written a monograph arguing that Lipperhey's real breakthrough was the invention of the aperture mask: The Long Route to the Invention of the Telescope. Galileo is known to have used aperture masks, and some earlier sources suggested that it was his invention. (Dunn mentions aperture masks on page 37, but is vague on when they first appeared.)
Another aside: One of the major figures in the book is William Hershel, who was a musician and composer before becoming an astronomer. You might enjoy listening to his music while you read this book: Herschel: Symphonies.