Many thanks to Barton Jones, an expert on jeweler's loupes, to allow me to publish this information here. If you are looking for a loupe, buy from him. His eBay store is here.
How to buy a jeweler's loupe
I have sold thousands of jeweler's loupes here on e-Bay. I am frustrated at the lack of knowledge some sellers show in their incorrect listings! Hopefully this guide will help you to know the truth about the loupes offered throughout e-Bay.
Loupes are generally listed by the strength of magnification or power first, ie: 10x 15x 20x 30x, etc.
The next number in the description is the size of the lens, or diamater of the lens at the top of the loupe, ie: 12 mm, 14 mm, 18 mm, 20.5 mm or 21 mm, etc.
The types of loupes are generally referred to as "Doublets", "Triplets", "Quadruplets" or "Pentagonal". This refers to the number of lenses built into the loupe assembly, (more on this subject later).
All loupes have a focal range, this indicates how far away from the object your viewing the lens will focus. This range generally decreases as the power of the loupe increases. (if the object your inspecting is upside down, try moving the loupe closer to the object, this should correct the problem).
Expected focal ranges are from 1/8 of a inch to about 1-1/4 inches from the object your inspecting. A good average averge is 3/8 inch or greater. The strong 20x or 30x loupes with a shorter focal range may block a lot of the light needed to inspect the object.
Lenses sometimes have special coatings to correct the color.
A doublet lens is constructed of a single piece of glass, with lenses ground on both ends of the glass.
Many lower cost loupes marked as triplets are actually doublets incorrectly marked as triplets, like the one pictured here on the left. The 10x 14 mm loupe on the right is a professional quality doublet.
A Triplet lens is constructed of three separate pieces of glass, mounted into one loupe assembly.
The three lenses are often glued together, but on the higher powered loupes spacers are used to separate one of the lenses. These picutres are from a 30x 21 mm triplet and a 10x 21 mm triplet.
This is a Pentagonal set of lenses, it has 2 sets of 2 lenses glued together and one single lens with spacers holding it in place in the center:
Shown on the left is a 20 x 12mm pentagonal loupe.
Quality: Most of the lower cost loupes are under powered, (ie: 10 x is really about a 7 x to 8 x power). They do not have optical quality glass and have no color correction coatings! These loupes are often advertised as "Professional" or "High" Quality!
Some ways to spot these lower quality loupes include:
- If the hinge is made of screws rather then roll pins it is most likely lower quality! (not always true, but their are very few exceptions).
- If the loupe comes in a hard plastic container rather then a leather case it is most likely lower quality.
- If the price is low and it's a new item, it's most likely lower quality. ( I can buy from 5 to 7 lower quality loupes for the cost of one professional quality loupe on the wholesale level from China).
- In many cases a lower quality loupe will serve your needs well, 7 x to 8 x might be enough power, and you may not need color correction coatings, so don't avoid all lower cost loupes! Just don't be upset when that is what you receive!
Some ways to spot a professional quality loupe:
- If it comes with a leather case it is more likley to be professional quality.
- If the hinges are made of roll pins rather then screws it is more likley to be professional quality (not always true, but often).
- If the cost is noticeably higher then the low cost loupes it is more likely a professional quality loupe.
- If the loupe has a name brand printed on it, with a higher price (over $30.00) it is most likely professional quality. If it's name brand under about $30.00 it could be a cheeper one stamped with a name brand if sold as new.
- If it looks exactly the same as a lower quality loupe, it most likely is the same.
A note on the constuction of loupes from China:
The metal used to construct the loupes is brass, coated with a chrome or gold color plating most often, (though the gold plating is not true gold). It can also be painted, black is a popular color for paint.
The lower quality loupes are made of window quality glass, the professional quality loupes are made of optical quality glass.
The screws used in the hinges will need tightend often, and some times fall out over time, if not checked often.