I use the Carson MicroBrite Plus LED Lighted Pocket Microscope, great for checking trichomes only cost like 14 USD. Hopefully, I answered your question and remember ..."Happy Growing" and "Free your mind one puff at a time"
You can also install an app called HiGrade, you pay a 1 time charge and they ship you a tool to add on your phone and with this tool and app you can take photos of the thc and actually read the % of thc that the plant has.
I have a 25mp camera on my samsung, and if you stand at the right distance for it to focus perfectly and you get a way to keep the phone steady, you can zoom in enough when u open the galery, so that you can actually check on trichomes.