Get a USB hand held microscop on Amazon. Its maybe . Then you can get up close and personal.
Strains very so ready up on your strain if you know it. Other wise here is a good rule of thumb for harvest.
When looking at tricombs ( 10% clear, 60% cloudy, 30% amber ) Thats best bet. HOWEVER again depending on strain it could be different, but I harvested when I had Mostly cloudy and no amber tri-combs and it was SUPER STONEY. So this is also a preference. Have fun and experiment.