Sir John Talbot's telescope
Larry looks through his father's telescope and spots Gwen (Evelyn Ankers) through her second story window. The body of the telescope is quite large in diameter (6 inches or more) and looks to be one that would allow the user to see some of the planets, like Venus and Mars, quite clearly. So wouldn't that telescope be too powerful to allow someone to clearly see a person from as close a distance as Larry was from Gwen?