The Donegan OptiVisor! Used by Jeweler's, Machinist's, Watchmaker's, Gunsmith's, Dentist's or anyone who works with small fine precision fitted parts. They do come in different focal lengths and there are charts to help you find what you need for what you are doing. The set I have is a #4 lens and has a focal length of 10" with a magnification of 2X. You can get increased magnifications but the more you magnify the closer the focal distance is, so be sure to find your optimal working distance you typically work at. There is a chart on their website so if you do order one read that first.
The different lenses are quick and easy to swap out and the headband is very comfortable and adjustable to fit anyone. Before I bought one of these about 20 years ago, I used to use one of the bench mounted magnifying circular lights. I still have it but have not really used it much since buying the OptiVisor.
I would strongly advise anyone interested in getting a GENUINE Donegan OptiVisor and NOT a Harbor Freight knock off!! When it comes to clarity, durability and longevity the Chinesium knock off's just don't hold a candle! It's a lifetime purchase and worth every penny - I have been using them religiously for 20+ years and there is rarely a day that goes by I do not use them - seriously! They are even more important when we age, get cataracts, loose close up vision, etc. They can be used with or without prescription lenses as there is plenty of room to accommodate glasses.
I am not affiliated with them in any way and don't benefit at all - I just like passing along information on really great products! This is one of them! They are the Bee's Knee's!!!!
ADDED: BTW, the lenses are made out of thick glass so they are very very scratch resistant and virtually impossible to break - believe me I've tried! lol

They are also very resistant to sparks and metal shavings from Grinders, Dremel's, etc. They are still in perfect shape!