I just use the macro function on my digital camera, gives you a great view of the trichs, and thus you can decide when to harvest to your liking (clear, milky or caramel)
Use a 30x loup and look at the trichs , you will want the heads to be milky looking instead of clear , when it hits mostly milky and a few amber Id chop it down for sure. I think thats when it is at its most potent, thats my opinion.