How can u know if a plant is ready to harvest without microscope

I don't generally use a scope, however a good zoom on a phone can tell you a lot. I usually, like smokeyspartacus, wait for the pistils to brown/shrivel up a bit and then the calyx are done swelling. Some strains will continue to push fresh pistils the entire time and then you have to make a judgement call. You should be able to see with your naked eye the difference between clear and cloudy with some practice.

Look at the buds themselves not the leaf. When you see the crystal on pistils turn milky. Hairs should be orange / red.

I never use microscope, many things impact when to harvest a plant but for starters i aim for 100% pistels to be brown and even then if the plant stil shows sign of good health i prospone it.