Reddit reviews Carson MicroMax 60x-100x LED Lighted Zoom Pocket Microscope For Field Inspection of Science, Fibers, Plants, Cells, Skin, Currency, Wildlife and More (MM-100)

• Laser Pointers - My top recomendation. They are fun to use at night if the person aiming them is mature enough not to point it at stupid things. They can be used for presenting stuff, but I have never found them to be needed for that. I like shiny bright stuff and my pets do too (even fish).
  
• Hand Held Microscopes - This is the one I got. What you get for the price is really pretty amazing to me. Other idea might be the ones that attach to your phone camera, but I've never tried that. The Carson handheld microscope is not professional quality, but for under $15, wow. Things that I've looked at: scratches on my electronic screens, leafs, dead bugs, cat hair, my skin, other peoples skin, textile, printed image quality, currency, and rocks. The quality is not the same as a microscope and you need to be really still or rest the scope on something. I can only use it at the lowest magnification without complaining. The benefits are it's portability and cheapness. Some people are not as interested by this.

There's only one way to know when a plant is actually finished it's optimal growing phase and it has NOTHING to do with it's size or it's colour or it's shape as all of that varies due to genetics and growing environment conditions. Get yourself a handheld 30x+ Microscope (every grow store sells them) and look at the trichomes. When they are 66% amber and 33% clouded the plant is done adding weight and terpene production. If they are still clear and glassy looking it's got some time to go.

That's not to say you can't take it earlier or later if you prefer, but it's not ACTUALLY done until it's done.

This is probably not the quality you're looking for but a field microscope is what you're looking for like this