Since you have the microscope...cool...You should harvest when you have a really good blend of clear.cloudy.amber trichs...the more cloudy/amber=more body high
...the more clear/cloudy trichs=more heady high...when you see amber trichs; then you start finishing for harvest...
It is a bit of judgement and a bit of personal taste...also, If I had a narcotic Indica, then I might go for more of a heady high...more clear trichs than amber...
If I have a heady sativa, then I might lean towards more amber trichs...See what I mean? I hope this helps you out, you have the right tool. Good Luck