yeah, a scope is needed if you really want to get down to the level of the trichomes which are anywhere from 20 - 200 microns in size. I would recommend not just checking a few buds either, check all over the plant if at all possible since i've run into single arms seeming to be ready to pull first. You want an all over average of about 50 - 60 percent amber heads. It is correct that a plant pulled with cloudy or clear trichome heads will be a "head buzz" type of smoke becoming more body as the trics develop. This basically means that you want a 50/50 of the colors. Plants allowed to get more than 80% amber are already headed down the path of less quality, so you should def pull them before that.
I'm running 1000w hps with some apollo 13 and vanilla kush, five weeks into flower with crazy amounts of crystal already developed. I use a 30x scope to check development, but jewelers loupe or something close would give a good view. It's pretty much impossible to really tell until you get down to at least 20x magnification.