明察秋毫

míngcháqiūháo
  1. lit. seeing clearly the downy feathers of autumn (idiom, from Mencius)
  2. fig. perceptive of even the finest detail

CEDICT

to perceive the minutest details

Wiktionary

目光敏锐，观察入微，可看见秋天鸟兽新长的毫毛。《孟子．梁惠王上》：「明足以察秋毫之末，而不见舆薪。」比喻能洞察一切，看出极细微的地方。《三侠五义．第四二回》：「不想相爷神目如电，早已明察秋毫，小人再也不敢隐瞒。」

重編國語辭典

Entry Composition

1 明察 míngchá
  1. to note clearly
  2. to perceive
2 秋毫 qiūháo
  1. fine hair grown by animals (or down grown by birds) in the fall
  2. (fig.) sth barely discernible
  3. the slightest thing
  4. the minutest detail