I had the good fortune to be born nearsighted, so until recently I didn't need magnification to build models. (I did, however, need glasses to recognize my wife from across the room.) In the past few years, though, I've noticed that it's harder to focus both eyes simultaneously on an object at close range. This, according to my optometrist, is due to a mysterious, insidious phenomenon known as getting old.
I've never been able to get along with Optivisor-type magnifiers, for two reasons. One - my eyes (like most people's) are different from each other, so the power of magnification that works for one doesn't work for the other. (Generic reading glasses don't work for me either, for the same reason.) Two - I've found that such magnifiers destroy my depth perception. If I'm trying to paint a detail under an Optivisor, for instance, I lose my perception of how far the brush is from the model. (I once watched a ship modeler at Mystic Seaport Maritime Museum working with an Optivisor, and asked him how he managed it. He grinned and said, "No problem. I'm used to judging depths with one eye. I'm blind in the other one.")
The solution for me turned out to be a gadget I found at a Woodcraft woodworking supply store (also available online at <www.woodcraft.com>). It's a simple pair of magnifying lenses with a clip in the middle that fasten to my regular prescription glasses - exactly like clip-on sunglasses. The prescription lenses take care of the difference between eyes, and the gadget flips up out of the way when I want to focus on something across the room.
If I remember right, the gadget cost about $10.00. I recommend it highly.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.