Perhaps the most important tool in gemology is that of the jeweler’s 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, an 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 jeweler’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.
An example of aplanatic correction is shown below. In the first block you see one of the cheap $10.00 loupes. As you can see, the edges get fuzzy and out of focus. Meaning that when you use this loupe you cannot see all of the gemstones across all of the field of vision. This is called aplanatic aberration and is a bad thing for a loupe to have. And all of the cheap ones have this problem.
Notice that the edges of the field of vision are fuzzy and out of focus. This is due to a cheap loupe and a very good reason for you to spend a few extra dollars and get you a proper quality jeweler’s loupe.
Now…notice the 18mm10x triplet as seen below and see how the type is focused to the edge of the field of vision. This loupe has a series of three lenses that join together to create a field of vision that is corrected to focus and color. I have not demonstrated the color correction due to the difficulty of imaging the effect properly. But I think these images are fairly graphic to demonstrate why you should invest in a good loupe.
Now that we know not to buy a cheap jeweler’s loupe and why…let us move on to learning how to properly use the jeweler’s loupe.
I can watch someone with a jeweler’s loupe for about 10 seconds and know just how experienced they are as jewelers and/or gemologists. Because the manner in which they use the loupe says a lot about how much they have used it…and how often they use it.