Every now and then we get a customer in the store who wants a very high power magnifier. Sometimes they bring printouts from other retailers that show some rather….unlikely high -power magnifiers with powers of 20x, 30x, even 50x. We unfortunately must inform them of the truth of these claims. The fact is – what is printed in the copy or actually on the magnifier is not true.
Oh, its not really the other companies fault – they are just going with what they see on the box and on the product. A typical example is this magnifier:
You’ll note this has a rather generous 30x magnification, which still having a nice, wide 21mm lens width.
Nonsense! The rules of optics are remarkably clear on this – the simple fact of the matter is that the more powerful a magnifier is (the higher its magnification) the short its focal length (the point where light rays passing through the lens meet on the other side of the lens) must be! And the shorter that focal length, the smaller the magnifying lens will be.
Let us elaborate:
A large handheld magnifier that probably everyone has in their drawer only provides about 2-3x and so has a long focal length of about 10″. Focal length equates to something known as ‘working distance’. What this means that you can use the magnifier about 10″ away from the thing you are viewing (this will vary slightly).
However, as you increase the magnification of the lens, the focal length of the lens must be made shorter – this also means the diameter of the lens must also shrink or else your lens will become excessively thick and will have a distorting shape – think of looking through a crystal ball and how messed up that image is. Its a good example of a wide diameter lens with a very small focal length (a ball lens, ineffect).
What this means is that by the time you get to just 10x magnification, your lens is barely over a 1/2″ in diameter. This triplet lens we sell is a good example:
The diameter is just 18mm on this unit, and in order to avoid image distortion the lens is a triplet design – where three lenses are placed together to make a much better image than one lens alone would provide. As you can see, the higher power we go, the smaller the lens is going to get. In reality, our 30x lens shown up top should really be about 4-5mm in diameter. Not a very big lens at all.
Truth to be told, barring some optical tricks (which I can assure these ’30X’ magnifiers do not employ) most magnifiers rarely go above 12-15x in power. That realm is reserved for low powered microscopes, which are a different optical beast altogether.
Unfortunately, big numbers sell, and so manufacturers keep putting unrealistic figures on their products knowing that most people won’t know any better. The real tragedy is that most of these overplayed magnifiers are not bad products! The 30X magnifier shown above is actually a decent 7-8X loupe magnifier. We’re even guilty at Spectrum of carrying a few of these ourselves – but in our product copy we note that the listed magnification is probably not accurate. We wish we didn’t have to do that, but we don’t like lying about a magnifier’s true abilities, we don’t like discarding a decent product, and our complaints to the manufacturer have fallen on deaf ears.
So remember these words when you are looking for a high-power magnifier. Don’t get suckered in by inflated claims and be realistic about what your lens can do!
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