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Trail talk: choosing a loupe

Three good loupes
Three good loupes

The study of many aspects of natural history, both indoors and in the field, can often be aided by the use of a magnifying lens, also called a hand lens, or loupe. There are cheap loupes and there are expensive loupes. There are really poor loupes and there are excellent loupes. What there isn’t, is a really good cheap loupe. But it is possible to buy one that isn’t too scarily expensive.

If you do want to carry a magnifying lens on nature walks, day walks or longer, multi-day backpacking trips, you may be tempted to carry and use a lens of the type used by thousands of children at school. This might typically be a simple wide lens in a lightweight plastic holder with a handle. There are benefits from this type of lens. They can be used with impunity; dropped and stood on, be clattered into a group box holding many dozen. One of these will inevitably eventually break, but even if it does, it is cheap to replace.

Plastic lenses may be cheap and lightweight, but they easily scratch, are difficult to clean without damage and will not provide the optical clarity that a glass lens will provide. Some people carry a very thin and light credit card sized, plastic ‘Fresnel’ type magnifying lens. These can also be useful for enlarging text or detail on maps, giving a wider view than the small magnifiers found on some base-plate compasses. But these simple lenses also introduce distortion. That said, for the mere casual observer of macro-natural history, a simple lens such as these may be all that you wish to carry and use.

For serious study of natural history, a glass hand lens, or loupe, should be used. For those people looking to decrease the weight they are carrying in the outdoors, the downsides are that loupes frequently have relatively heavy metal frames and glass is also heavier, and optical glass is a good deal more expensive. Good quality magnifying lenses have been made with care. This is an expensive process and optical coatings increase this cost. While a loupe can be a relatively expensive purchase, if chosen carefully, it can be a one-time buy and will, with care, last a lifetime. A purpose built case, often leather, will protect a loupe from knocks and scratches and a neck strap will stop it being lost in the undergrowth. Neither of these are essential accessories of course.

What is a loupe?

It helps to first have a little understanding of what a loupe is. In essence, a loupe (pronounced loop) is a magnifying hand lens in a holder. A quality loupe will give a clearer close-up image with little in the way of distortion. A good lens will enable the close-up study of flowers and leaves, insects and spiders, aid in the determination of the necessary features to identify species. A loupe can also be used in geology, with gemstones and also antique and classic watch buying if that is your thing. Three Points of the Compass collects map measurers (and blogs on these each month), a loupe may be used for studying these. Some loupes will have tiny LEDs built into them. Powered by small batteries, these will provide more light when studying an object and can be useful in low light conditions. As such, LED loupes may be more suitable for indoors use as there is less of an issue with low light ‘in the field’.

Using a loupe to check on hidden fine detail on a map measure
Using a x10 loupe to check on fine detail on a map measure

Lenses

Loupes will use either one lens (singlet), two lenses (doublet) or three lenses (triplet). The use of four lenses (quadruplet) is extremely uncommon in loupes. Each individual lens is shaped to one purpose. The main lens will magnify, a second or third lens will correct anomalies. Stay clear of singlet loupes which suffer image distortion that can be easily avoided by purchasing a doublet or triplet. So- two lens good, three lens best. It is unsurprising that many of the best loupes and the best lens are produced by the companies also making high end photography equipment, binoculars, telescopes and specialised optical equipment. Premier brands Bauch & Lomb, Zeiss and Nikon produce good, quite expensive loupes while middle-market Opticron also make good and slightly cheaper loupes, as do many other well-known reputable manufacturers.

Lenses introduce anomalies into what is being viewed. A single lens will split colour (chromatic aberration) just like a prism and also distort straight lines (planatic aberration). A loupe will incorporate multiple optical glass lenses to correct these anomalies and provide a clearer sharper image. Not always found in loupes, an aplanatic lens will minimize two monochromatic wavefront errors, called spherical aberration and coma, and provides a wider distortion free field of view. An achromatic lens is corrected for colour distortions and permits near true colour viewing. If a specification states that a loupe is aplanatic or achromatic, it has been corrected for aberration.

The prism effect of chromatic aberration created by a single lens. Different wavelengths of colour are bent by different amounts.
The prism effect of chromatic aberration created by a single lens. Different wavelengths of colour are bent by different amounts.

A combination of lenses, when correctly engineered, ensure that the light (colour) coming out is corrected and no longer split, this is an achromatic lens. You might see some loupes advertised as having Coddington lenses. These have two pieces of glass bonded together. Despite being shaped to minimise distortion they are not achromatic and some colour distortion will be experienced. As such, it is best to simply avoid them as there are better loupes available for comparable cost.

Lenses corrected for spherical aberrations will permit a larger field of view, from side to side. Doublet and triplet loupes are designed so that individual lenses can be manufactured to differing criteria, even of different materials or specification of glass, possibly also having different coatings. Because each lens is individually optimised for different wavelengths, they are held together in a supporting frame, usually with protective covers. This normally incorporates an internal air space between each lens that permits them to have non-matching curvatures. This has the secondary effect of making loupes quite bulky when compared to a simple single magnifying lens. A grey or black internally coloured frame will reduce glare and reflections, while a silver frame will encourage more light around the object being viewed but may also introduce reflections and lens flare. The frame may be plastic (cheaper, less durable, lighter) or metal (more expensive, durable, heavier). Some loupes may also incorporate tiny LEDs to provide lighting for a subject.

Depth of field is the distance between the closest and farthest part of an object that is in focus and is particular to each loupe. It is something that is rarely advertised and difficult to quantify. I have found that provided it is not too short, a problem exacerbated by higher strength magnifiers, then it can be adjusted for when in use. All that you can really do, is try a lens and see if it is acceptable to you. There are other aberrations that are more important.

If there is one thing to draw from the above, it is look carefully at the specifications of any loupe you are considering buying.

What magnification to choose?

Loupes come in various magnifications. Something of 5x or less simply isn’t worth bothering with. A 20x can be difficult to use as they have a narrow field of view and a less useful smaller viewing image often with greater distortion toward the edges. The ideal magnification to choose for nature study is 10x.

Three Points of the Compass has a number of loupes, purchased and used over the past four decades, but anyone coming to these anew, need only purchase one and with care, it will last you a lifetime. I have bought and been given cheaper loupes over the years but eventually moved on to a very small selection of middle-range lens that do me well. I have now left serious academic use far behind me and am now strictly an occasional amateur naturalist. I suggest below three loupes that offer good quality for a reasonable price. There are far cheaper loupes available and far more expensive ones too. But the three looked at here are all good choices and any one of these would make a good purchase.

Opticron Hand Lens 23mm, x10

Opticron 10x23mm loupe
Opticron 10x23mm loupe

The Opticron 10x Hand Lens is an extremely well-priced doublet loupe. Opticron have a decent reputation for their middle-market optics and if you are hesitantly dipping into macro study of nature, this simple little magnifier won’t break the bank. It has an aluminium alloy case wrapped around a polycarbonate body. There is a small loop on the end of the metal case through which a thin wrist or neck strap could be passed. The rotating case is held in place with one tiny Phillips screw. Some users report that this can work loose and be lost. Lenses and body are made in China. I confess to being unsure what the lenses are made of. Opticron and most sellers state that the lenses are made of glass, however it has been suggested they are coated PMMA (polymethyl methacrylate), also known as plexiglas® or acrylic.

Opticron 10x23mm loupe
Opticron 10x23mm loupe
Opticron 10x23mm loupe

Due to its simple construction involving just two lenses held in a plastic body there is just a touch of planatic aberration introducing straight line distortion and also some chromatic aberration however these will be acceptable to most. Actual Field of View is approximately 20mm and the widest of the three loupes looked at there. Focal length is 15mm.

This is quite a narrow loupe and the small case is more suited to smaller hands and fingers. The compromise between low cost and quality has made this loupe a favourite for many Field Studies groups. The loupe weighs just 31.6g and is the lightest of the three loupes suggested here. It measures 38.7mm x 26.5mm x 19.15mm. Opticron also make a 10 x 18mm loupe and a 10 x 21mm LED version. All of these loupes have a two-year warranty.

Opticron doublet 10x23mm loupe
Opticron doublet 10x23mm loupe
The 16.5mm space in the case is insufficient for me to comfortably loop an index finger through
The 16.5mm gap in the frame of the Opticron 10x23mm is insufficient for me to comfortably loop an index finger through

While just about any purpose-built neck lanyard could be used, Opticron do make a 7mm wide nylon neck lanyard that costs less than a fiver. White in colour, it will quickly look a bit grubby. Cheaper black coloured neck lanyards are easily available elsewhere. A brightly coloured lanyard would show up better in long vegetation if dropped, that might be a consideration for some.

Kite Triplet hand lens, x10

Kite 10x Triplet loupe
Kite 10x Triplet loupe

The Kite Triplet loupe from Belgium company Kite Optics is made at Kite’s manufacturing plant in Japan and has achromatic/aplanatic lens type. It has a 10x magnification and weighs 34.4g. The loupe has a black coated aluminium housing held together by rivets. This loupe has a stipulated 21mm linear Field of View, nearer to 19.5 in actual use with a focal length of 27.78mm.

Kite 10x Triplet
Kite 10x Triplet
Kite 10x Triplet

The matt black external and internal finish cuts down reflections and flare while studying items however I can get some lens flare on the upper lens on a bright day. There is a small metal loop at the end of the housing so can be hung from a neck loop for safety. It comes with a well-made brown leather carrying/storage case, stitched together, with a brass popper closure. The case weighs a further 15.5g. When closed, loupe dimensions are 35.7mm x 24.6mm x 24mm. In a decent range of six loupes, Kite also includes a cheaper inachromatic/aplanatic 10x doublet loupe and more expensive achromatic/aplanatic 10x triplet with LEDs. The Kite Triplet comes with a two-year warranty.

Kite Optics triplet 10x loupe. There is negligible planatic aberration
Kite Optics triplet x10 loupe.
Kite 10x Triplet with case
Kite 10x Triplet with case
Kite 10x Triplet
22mm gap in case is comfortable to hold with an index finger looped through
22mm gap in frame is comfortable to hold with an index finger looped through the Kite Triplet

Belomo Triplet loupe, x10 (LP-3-10)

Belomo Triplet x10 loupe
Belomo Triplet x10 loupe

The name Belomo is formed from the words Belarusian Optical and Mechanical Association (BelOMO). They are a long-standing manufacturer of highly respected optical lenses used in loupes, binoculars, telescopes, cameras and other equipment including weaponry. All lenses are inspected once manufactured and each one is certified.

Belomo Triplet x10 in the hand, closed
Belomo Triplet x10 in the hand, closed
Belomo Triplet x10 in the hand, open
Belomo Triplet x10 in the hand, open

Coated anti-reflection, achromatic lenses are fitted to the Belomo loupe that permit viewing true to life colours. Very little spherical or planatic aberration is experienced with this loupe and it is more than acceptable for all but the most demanding. This ‘x10’ loupe actually has a magnification closer to x9. It has an advertised 17mm linear Field of View, however I believe it is wider, nearer 19mm, and has a focal length of 28mm. This loupe has good light casting on a subject despite having a mostly dark interior ring. Two silver-coloured internal rings do a good job of brightening viewing.

The Belomo Triplet loupe has a steel frame with a (hidden) plastic interior. This loupe uses screws rather than rivets in its construction, meaning that these can be tightened and loosened as required, something that is not possible with the rivets commonly found in loupes from many other manufacturers. Screws are fixed in place so will not loosen of their own accord until ‘tweaked’ for the first time.

Belomo Triplet x10 loupe.
Belomo Triplet x10 loupe.

Belomo products come out of Belarus. There are now many people reluctant to support such a market due to the support that Belarus provided Russia in their offensive against Ukraine. If you can move beyond that, their products are both high quality and good value. This loupe is a great favourite with many, it is also the one that Three Points of the Compass reaches for most frequently.

The Belomo Triplet can also be purchased with a quite large brown leather carry/storage case. This is stitched and oozes quality. Closed via a metal popper, the case also has an embossed Belomo logo on the side. Another accessory for the loupe is a wide nylon neck lanyard. Neither case nor lanyard are essential elements, and the loupe is a far cheaper purchase without them. Belomo products have an eighteen-month warranty but you may struggle with getting repairs etc. carried out.

Belomo Triplet loupe with leather case
Belomo Triplet loupe with leather case
Belomo Triplet also fits the leather Kite Optics case
Belomo Triplet also fits the leather Kite x10 case
Belomo Triplet "Made in Belarus"
Triplet is very well constructed and can be partly dismantled for maintenance and repair
Triplet is very well constructed and can be partly dismantled for maintenance and repair

Dimensions are 36mm x 28mm x 25mm and it weighs 40.2g. It is an angular loupe but comfortable in the hand. It also looks quite handsome with a textured cracked-black finish. The frame is held together by four screws which are prevented from loosening by a threadlocking adhesive when fresh out of the factory. If loosening or tightening screws you might want to consider a drip of Loctite when doing so. There is no included loop for a neck lanyard, I just loop a third-party lanyard through the frame pin.

Belomo Triplet x10 in the hand
19mm gap in the frame is just enough for me to comfortably hold the Belomo Triplet x10 in the hand

Any of the three loupes above would make a good purchase for someone looking for a decent but well-priced loupe. There are cheaper available but the adage, buy once, cry once applies here. There are also certainly many more expensive loupes. However, for most of those interested in closer study of natural history, there isn’t much requirement to look further than one of these three.

How to use a loupe:

While some users like to grip the lens case between thumb and finger in use, or grip each side of the frame, Three Points of the Compass prefers to loop a finger though the frame not only for security, meaning it is more difficult to drop the loupe, but also because I can brace my hand against my cheek while using the lens. The correct use of a loupe is a very necessary and simple skill to learn. It is also only too apparent that many people have never learnt it.

  • Rotate the lens part of the loupe out of the frame and loop the index finger through the frame of the loupe (or in whatever manner you prefer).
  • Bring the loupe close to the eye. The loupe shouldn’t touch the eye but should be as close as possible. If a glasses wearer, either remove the glasses, or rest the loupe against or very close to the glasses. Rest the hand against the cheek to steady the view.
  • Keep both eyes open. This reduces eye strain.
  • Bring the object to be studied toward the loupe until in focus. Alternatively, move the entire head with loupe held in position, toward the object to be studied, until in focus.
A decent neck lanyard need cost no more than a couple of pounds
A decent neck lanyard need not cost much. This one was £1.50 and weighs just 7g

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