Is loupe a loupe a loupe?

Canuck

One type of lens that is preferred by many is called an aplanatic lens. A loupe with an aplanatic lens looks pretty much like any loupe. But an aplanatic lens is more money. The benefit with these lenses is lack of distortion of the image for the full breadth of field. Many lenses give sharp focus at the center of the lens, but less sharp around the perimeter of the image. Aplanatic lenses solve that problem. Gemologists often use aplanatic lenses in their work.

A good example of distortion created by a lens that is not aplanatic is an image earlier in this thread. Notice how the centre of the image is well focussed, while the perimeter is blurred.

Fritz

Thanks for that explanation, it solves a little mystery we had last year.

I bought a pair of Bausch and Lomb loops for use in the shop, it keeps the shop monkeys from trying to borrow my stuff if you keep them supplied. The distortion as you moved away from center was so bad that they were returned to the vendor, the replacements sent free of charge went in the garbage pretty quickly. Now I know why.

It’s a little depressing to buy a respected brand name at a hefty price and get junk.