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Tips for selecting a hand lens magnifier

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What is a hand lens magnifier? The most important hand lens tip Magnification power Lens diameter Doublet, Hastings triplet, and  Coddington hand lenses Body and case construction Lanyards, pocket cases Using a hand lens

Hand lenses are the basic magnifier for many earth science field studies. Geologists, biologists, entomologists, and others use them to make quick identification of small distinguishing features which would otherwise be too small to see with the unaided eye. A hand lens is more closely related to microscopes than it is to a standard magnifier or "reading glass" because it is designed to provide relatively high magnification of a small area rather than low magnification of a large area.  For science use, a good quality hand lens is essential, otherwise your efforts to see something will result in frustration rather than knowledge. Here we will talk mostly about a hand lens for field geology use, but the principles apply to other earth science hand lens uses.  Some people refer to hand lenses as loupes, jeweler's loupes, or  eye loupes.

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The most important tip about selecting a hand lens is to get a quality lens.  Unfortunately there are a great many low quality hand lenses for sale out there.  Some we have seen use a lens not much different from a clear glass marble.  You won't be very happy.  Fortunately, most of the really unsatisfactory ones are sold at low prices which should be fair warning.  Even though you won't be out much money, a poor hand lens will distract from your use of it in the field. Usually the low cost hand lenses also have a rather flimsy housing of chrome plated die cast metal which will fairly easily break.  But some are put up in fairly well made housings and  are even labelled as "Triplet" or "Three element" or "Four element" hand lenses.  We have taken some of these apart and found, guess what, pretty much a clear glass marble for a lens. The 10x Bausch & Lomb Hastings triplet is our personal choice, but all of the hand lenses that we supply are high quality instruments that we are willing to use ourselves.

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Magnification: Hand lenses are available in magnifications from 7X to 20X.  The higher the magnification, the more difficult it becomes to use a hand lens.  First, the more power the magnifier has, the less depth of field of focus you have available to work with.  This can be OK for very flat objects such as postage stamps, but makes it tough to use with three dimensional objects such as rough rock surfaces, bugs, or flower parts.  Secondly, unless you are an expert that has developed the need and the skill to pick out some really subtle details, you will seldom get any more information out of what you are looking at than 10X can provide..  7X hand lenses are often chosen by biologists looking at 3D objects because the lower magnification provides a deeper depth of focus.  7X is also a good choice for teaching proper hand lens use to youngsters because  the larger diameter makes it easier for the object to get enough light to view easily.. 10X hand lenses are a good all around choice for most people.  Most of the hand lenses used by jewlers are 10X. 14X or 15X hand lenses can be an asset for experienced users, most of whom already have a good 10X.  20X  Is recommended only for well trained users who need the extra magnification for a specific purpose.  We would expect that these people have a lower power hand lens for general use.

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Lens Diameter: For geology, and most outdoor field uses, a hand lens of around 13 mm to 18 mm diameter is a reasonable choice. There are larger diameter magnifiers made, but often the optically usable part of the lens is a smaller area near the center.  Larger magnifiers do make it easier to get sufficient light on the subject, but there is always a trade off. For example the 20X Bausch and Lomb Hastings Triplet has excellent optics, but is only about 8.3 mm in diameter, making it tricky to use in poor lighting conditions.  The 20X economy triplet we sell is 18mm in diameter making it easier to use in poor light conditions, but only a small part near the center of the lens produces the best image.

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Doublet, Hastings Triplet, and Coddington All lenses are compromises.  Bending light rays to provide magnification always introduces some other kind of distortion in the image.  The way lens designers get around this problem is to use multiple lens elements, so one element can correct for some of the problems introduced by another element. Doublet hand lenses use two separate lenses, separated by an air gap.  It is a cost effective way to make a good hand lens.  But eventually dirt or moisture will get in between the two lenses, and you will need to take it apart for cleaning.  It usually isn't a problem for a lens used indoors. Sometimes you will find another type of doublet called an "achromat" which has the two lens elements cemented together, but they are not common. A variation used in some three element triplets is to use a cemented achromat element for color correction, and add a third un cemented element to raise the magnification to a higher power such as 15x or 20x Hastings Triplet hand lenses use three glass lens elements.  The triplet part refers to the three elements, and the Hastings part refers to the name of the person that came up with the particular design.  There are other triplet designs for other optical purposes, but Hastings Triplet is the common one for hand lenses. The three lens elements of the lens are usually, but not always, cemented together with clear cement so that no dirt or moisture can get between the lens elements. Usually trouble free, but you wouldn't want to use a Hastings triplet in a constantly wet environment or the cement may start to degrade. Coddington is another lens system named for the person who devised it.  The Coddington design is a pretty ingenious method of making a single glass element behave as if it were a multiple element lens.  The advantage of the Coddington for earth science users working in wet environments is that it is pretty much impervious to moisture.  The way a Coddington  works is by forming curved lens surfaces on the top and bottom of the lens blank, and then grinding additional lens surfaces part way into the perimeter of the lens blank.  That optical trick produces a pretty good magnifier at much less cost than grinding and assembling three separate lens elements.  But with all lenses there are compromises, and with the Coddington the usable diameter of the lens area is quite a bit less than the diameter of the glass blank.  The part you can't use is painted black.  On the other hand, the groove in the perimeter makes a place to place a small light bulb to make an illuminated Coddington magnifier. Four or five element hand lenses are advertised.  We haven't taken one apart to check if they actually do contain all the elements.  What we know is that a good Hastings triplet is an excellent hand lens, and we don't see any advantage to paying more for a hand lens that has more elements.  What you really care about is the quality of a hand lens image, not how many elements it contains.

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Hand Lens Body and Case Construction: Kooter can get an idea how much field experience a student has had by noticing if their hand lens is still folded into its case on their neck lanyard.  If it is still folded into the case, the magnifier has not had much use. After a little time, you will find that the original friction at the case pivot is pretty much gone, and the lens barrel dangles unprotected for the rest of its life. This means you are looking for substantial construction of the barrel, pivot, and glass lenses. Pivot construction is important, because even though you can't keep the lens from swinging out of the case, those pivots are all that keep your hand lens from separating from the case and getting lost. If the pivot is well riveted as in the Bausch & Lomb magnifiers and our economy hastings triplets, you are probably OK for a long time. If it is a threaded post, such as used on the Sina doublet, it may come unscrewed without noticing until it is too late. We recommend you check the screw of the Sina often, or unscrew the pivot and reassemble it with a drop of nail polish to lock the threads. Body construction is important.  Many  cheap magnifiers use a die-cast body with friction rings to secure the lenses.  The die-cast material is brittle and breaks easily, and the ring sometimes lose their grip and let the lens elements fall out.  Bausch & Lomb hand lenses use a lightweight but rugged plastic lens barrel that we have never seen fail. The economy hastings triplet and Sina hand lens use a machined brass magnifier body and threaded lens retainer rings.  It is a little on the heavy side, but makes for a quite rugged magnifier construction.

Lanyards and pocket cases We have always used a hand lens with a neck lanyard to keep it handy for quick use.  In fact we supply a free lanyard with each hand lens we sell because lanyards can sometimes be hard to find locally.  A shoe lace or other cord would work in a pinch..  Some people suggest that your hand lens lanyard should have a break-away feature which is often used for security badges, in  order to avoid a potential injury in case you fall over a cliff and the lanyard snags on a tree root or something..  Our free lanyards don't have the break away feature, so don't use it if you don't feel safe.  In the last twelve years we have seen field accidents including broken ankles, asthma attack, bee sting allergy attack,  heat exhaustion or dehydration, and even one very nasty multiple ratttle snake bite incident.  But never an injury involving a hand lens lanyard.  Could happen though. Some people want a pocket case for their hand lens.  We have never used one ourselves, so don't know what the advantage might be.  Our economy triplets are supplied with a pocket case, but we suspect that most of them are discarded.  Bausch & Lomb does not supply pocket cases for their hand lenses.

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Using a hand lens A hand lens is optically related to a microscope.  So just like a microscope, your eye should be close to one side of the lens and the object will be close to the other side of the lens.  With a little practice you will get the hang of manipulating the object and hand lens to get things into focus. We have seen people use a hand lens like a reading glass magnifier, with the hand lens held away from the body.  It works up to a point, but you won't see the same thing as you would by using it properly.  The main problem with using a hand lens is getting the right light on the object.  In bright sunlight you will have to manuver around to find a position where the object is not in your own shade or the shade of your hat, but the bright sun is not shining into your eyes and making it difficult to see. For basic geology studies, the hand lens is part of a simple system for quick mineral identification. For example you might have a hand specimen of a rock, and need to classify it as a siliclastic or a carbonate. Starting with an acid bottle test, a drop of acid might make the specimen fizz, usually indicating a carbonate. But then you would take a look with your hand lens to see if there are sand grains present, because the fizzing may only be the result of calcite cement between the grains. On the other hand, a rock sample might not fizz until you powder some of it.  If that happens, then you would use your magnifier to look for carbonate dolomite crystals that don't react well with the acid unless powdered. In addition to mineralogy, a hand lens lets you pick out clues to stratigraphy based on grain shape and size, or micro fossils, and it will be used often while traversing a section as you make observations and take notes.

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