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

目光敏銳，觀察入微，可看見秋天鳥獸新長的毫毛。《孟子．梁惠王上》：「明足以察秋毫之末，而不見輿薪。」比喻能洞察一切，看出極細微的地方。《三俠五義．第四二回》：「不想相爺神目如電，早已明察秋毫，小人再也不敢隱瞞。」

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