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SPECIFICATIONS: Perhaps the most important tool in gemology is that of the jewellers loupe...pronounced "LOOP". This most important piece of equipment...in the right hands...can serve as the foremost identification and grading tool. There are two important factors about making the decision regarding which loupe is right for you. The first is the size of the lens. Most good quality loupes will have an 18mm lens in 10x or 10 power. This is the standard for most gemologists...however, larger and smaller size lenses are available. And loupes in the 20x or 30x are available....but not worth much because the lenses have to be so small at the higher magnification that they are not much use. So a 18mm 10x loupe is the first consideration. Second, is the optical quality of the lenses. The cheap loupes you find on eBay or elsewhere that sell for a few dollars are worth what you are paying. Mainly because the optics are cheap and the lenses have not been corrected for aplanatic and achromatic aberrations. WHATS THAT?...you may be asking. This is where three lenses are used to make the better quality jeweller's loupe that correct the lenses so that the field of vision is in focus all the way to the edges, and so that the lenses do not impart false color to what you are seeing.