Col. Potter's binoculars

Answer 1

Actually, the binocular scene in question is from Season 5, episode 7 entitled, "Dear Sigmund", where Dr. Sidney Freedman is writing a letter to Sigmund Freud about the 4077th and how they deal with stress and one of the ways is through practical jokes, including the Potter binoculars that send Radar into hysterics.  This is also the episode where Burns digs a foxhole, which Honeycutt fills with water and Sidney yells "Air raid!" which sends a panicked Frank jumping out of bed and diving headfirst into the hole.

Answer 2

The "binocular" scene was shown only in that episode during season 7, which was actually an hour long (or 2-parter for syndication) clip show that included scenes that didn't make the cut on any other episodes, whether because they didn't fit into time constraints or distracted from other storylines.  That particular clip show used many "deleted scenes" that enabled producers to fulfill a requirement for an episode, and it also happened to be shown during  "sweeps week", which is when shows put on their best episodes to attract more viewers (which also determine advertising rates for the rest of the season.)  In this case, I think it's say to say it worked since MASH remained #1 for another 5 years and went out on top.