you need a 30x jewelers loupe to see the trichomes and judge when to harvest. most people harvest from 5%-30% amber trichomes. harvest at 5%-15% amber trichomes for a "head high" energetic effect and harvest at 30%-50% amber trichomes for a "body stone" sedative effect strain dependent.
https://www.google.com search 30x jewelers loupe
https://www.google.com search 30x jewelers loupe