Q. If a tree belongs to a Gentile, and you are not entering his property, but just standing next to his tree while he is watching you. do you need his permission to make a brocho on his tre?
Can you make a brocho on the tree of a neighbor if you can only see it with binoculars?

A. Horav Shlomo Miller’s Shlit’a opinion is that there is no issue of trespassing by just standing in the public street, looking at the someone’s tree and reciting a brocho. However, common sense should reign, to avoid a lengthy and numerously attended ceremony that the present homeowner may dislike and resent.
Ateres Paz (p. 224) quotes Horav O. Yosef zt’l that one recites birchas hailonos when observing the flowering fruit trees using binoculars or a monocular tube. Avnei Chen (26: 20), distinguishes between simple straight telescopes and the more evolved instruments that employ mirrors and the reflection of prisms. Pesach Hadbir (224: 10) equally permits their use for the brocho recited on a king.
Horav Shlomo Miller’s Shlit’a opinion is similar. The Rov also wrote a teshuva in Maayanei Shlomo (O.H. 77) in regards to different halachos involved in the use of mirrors and lenses.

Rabbi A. Bartfeld as advised by Horav Shlomo Miller Shlit’a