10 weeks flowering.... harvest?

Hey guys im 10 weeks flowering and have been watching the trichs with this gay as michro. from radio shack. It like 100x but small window im having trouble deciding if they are turning milky or not, but alittle concered on how long its taking. My leaves are starting to turn yellow, mainly on the lower half of the plant and the bigger fans only. Ive stopped nutes a few weeks ago and the buds are looking pretty good expecially for using florecent light, i know its not ideal im working on better. plants about 4 feet tall and maybe 1/4 pound at best. Any body if and advise or experiences they would like to share?

sorry no pics

Oh and a few weeks ago the leaves really started to turn purple right around the time that the bigger fans started to turn yellow and die.