HOW TO CHOOSE A MAGNIFIER
Choosing and using a magnifier: loupes, eyeglasses, reading glasses, binocular magnifiers.
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CONTENTS OF THIS ARTICLE:
The size of a magnifier is given as two figures, e.g. 10X18. The first figure is the magnification, the second figure is the diameter of the lens in millimeters. So 10X18 means that the magnification is 10X (makes items appear ten times larger than normal) and the lens size is 18mm diameter.
Sometime the lens is square. You will still see the magnification followed by the lens size, as above, but it will look something like this: 2X 80X80 (that would mean 2X magnification with a lens size of 80mm X 80mm).
exactly the same applies to binoculars and telescopes, the 'diameter'
being that of the big lens (the objective lens) so a "7X50"
binocular or telescope has a magnification of 7X and objective lens
diameter(s) of 50mm.
These are the wrong questions.
The questions should be, "What magnification do I need?" and "How does the quality (how clearly I will see) vary? - and is a powerful magnifier as 'clear' as a less powerful magnified? - and are there different types of magnifier?
Don't be embarrassed if you get the names wrong, nearly everyone confuses a loupe with an eyeglass, most people refer to 'the flat magnifier' when they mean Fresnel, or 'the thing you stick round your head' when they mean 'headband magnifier'.
Here are the true names.
Any magnifier large enough to read text (e.g. newspapers, tins in a supermarket) is a 'reading magnifier'. Some are large with handles (readers), some fold or slide into cases (general purpose folding magnifiers), some are small (30mm across), some are large (a few inches). One interesting variation is the 'Fresnel' (pronounced Fren-nel because it's French), a flat sheet of magnifying plastic, the size can be credit-card size up to page-size. Whatever the variation, these are all 'reading magnifiers'.
A loupe (pronounced 'loop' in this country) is a small folding magnifier (from 12mm to 21mm diameter) of high magnification (usually about 10X) which folds into a metal or plastic case; these are used by jewellers for reading small marks and are often called jewellers' loupes. An eyeglass (often called a watchmakers' eyeglass) is a cone of plastic, you hold the open end in your eye (it takes practice!) and this leaves your hands free to work, the IDEA is that there is enough working distance (space between the lens and the object) to use of tools. In order for there to be a large working distance, the magnification must be low (more about this later).
As a guide to quality, both loupes and eyeglasses start at at £2.00 but the best eyeglasses cost £5.00 whereas a good quality loupe costs £20.00 and the best quality £89.00 (quality is paramount when viewing gemstones and diamonds or detecting the more 'difficult' forgeries in stamps and coins).
Finally, hands-free magnifiers. Most of the magnifiers listed above come in hands-free versions. There are eyeglasses that clip to spectacles and loupes that clip to spectacles, there are large readers on stands (with or without lights), binocular headband magnifiers] that fit around the head, and even one that hangs around the neck (good for reading, sewing, embroidery and fly-tying).
Apart from deciding on the APPROXIMATE magnification (2X or 10X) and APPROXIMATE size (pocket-size or page-size) and APPROXIMATE quality (£2.00 or £20.00) there is no rule about which type of magnifier to use. Some professional engineers buy the cheapest largest reading magnifier because they don't like to spend money, some hobbyists will spend £89.00 on a Zeiss 10X20 loupe because they want the best and they can afford it.
With a large magnifier (e.g. for reading books, small print etc) hold the magnifier part way between your eye and the object. Now move the magnifier very slowly backwards and forwards until you have the best image, not too small, not too fuzzy. The idea with a large reading magnifier is to set up straight, sit comfortably, you should not have to bend over the magnifier and peer closely (though it depends on the quality of the lens).
With a strong magnifier (e.g. a jewellers loupe) hold the magnifier as close to your eye as possible (if you wear spectacles you may leave them on or take them off, whichever is the most comfortable). Next, bring the object very close to the magnifier, so close that it's almost touching. Finally, very slowly move the object away until it is in focus.
Lighting is as important as magnification, as important as quality, without good light you won't see much, even through the most expensive magnifier. Ideally you need bright daylight or bright diffuse ceiling lights or a table light close to the object. The light must be between the magnifier and the object, do not shine the light at the top of the magnifier, you will merely be blinded by reflections.
If you are a trader buying at pre-dawn fairs or viewing in dimly-lit auction halls, you will benefit from a magnifier with a built in light; if you are partially-sighted and don't have a correctly-positioned table light, then you must use a magnifier with a built in light.
Magnifiers with built in lights come in large sizes (reading magnifiers) or small sizes (jewellers loupes or a watchmaker's eyeglass). You could, of course, simply use a torch, but then you would need one hand to hold the torch, one to hold the magnifier and a third hand to hold the item. For hands-free use, there are magnifiers that fit around the head or clip-to-spectacles or plug into the mains.
When using a handheld illuminated magnifier, do remember to hold it with the light shining towards the object and not into your eyes - I know this sounds obvious, but a significant percentage of customers at the QUICKTEST stand get it wrong, they shine the light into their eyes then complain that the light is blinding them and they can't see anything.
Two rules. Firstly large lenses made of glass are heavy whereas plastic is lightweight. Of course, plastic scratches easily, glass doesn't. But don't think that a lens has to be made of glass to be any good, the most expensive lenses (e.g. Zeiss jewellers loupes at £89.00) are made of plastic ...though 'plastic' sounds too down market so I say "high grade optical acrylic".
Secondly, magnification, size and working distance. The more powerful the lens, the smaller it will be and the closer you must hold it to the object ('working distance'). The less powerful the lens, the larger it will be and the further you can hold it from the object. Read that again, memorise it - it applies to all simple-lens magnifiers. There is always a compromise between high magnification (small lens) and large lens (low magnification).
These are the rules. They are not my rules. They are the rules of physics, there is no way around them - IF YOU WANT A SIMPLE HANDHELD MAGNIFIER. If you want a powerful magnifier that is large and / or has a long working distance, there are three types, as follows.
A head-worn magnifier made out of two little telescopes as used by surgeons (Surgeons' Magnifiers); a high quality low-power microscope (I often have various models secondhand); a camera that connects to a computer or TV to enlarge print in a book or newspaper.
You will notice that we sell a new pocket microscope with a magnification of 30X, and a large microscope with magnifications (selectable) of 2X, 4X and 6X. And you might notice that our 30X microscopes sell for £5.00 and the 2X, 4X, 6X microscope sells for £1440.00. This is because it is always the quality of the optics you pay for, not the power of the lens. This applies not only to microscopes but to simple handheld magnifiers.
When you look through a lens don't simply marvel at 'how large' everything appears. Look to see if faint objects show up against the background or are fuzzy; if straight lines appear straight or curved; if the image is clear around the edges of the lens or wobbly; if colours are true. Lighting is important too. If you are using an illuminated magnifier, is the light bright enough, and does it actually illuminate the object...even when the magnifier is tilted at different angles? These are the differences between the cheapest and most expensive lenses. If you buy by mail and the magnifier turns out to be unsuitable, you can return it, or you can see for yourself by trying them out at the QUICKTEST stand at the antiques fairs.
We are specialist optical dealers and very fussy about the quality of our triplet (and 4-element) loupes. I have samples of 'triplets' from a supplier specialising in triplet lenses and claiming that only they supply genuine 'triplets' - and I can see immediately that they are very poor optical quality, and I have dismantled them and the lenses are not triplets! If you have bought one of them, buy one of ours too, compare the two, and return the one you don't want. Similarly there are many antiques fairs and street markets where you can buy lenses marked "10X" and "30X" magnification and even "Zeiss" - they are not as described, but unless you buy the genuine article you will never know just how awful they are!
The following applies to simple lenses, including all jewellers loupes. The following does not apply to 'surgeons' magnifiers which are made of two small telescopes.
THE 14 INCH RULE
Some magnifiers are marked with the magnification, some are marked with the focal length (working distance) in inches.
The focal length (working distance) is the ideal distance between the lens and the object, not too close (or the lens won't magnify) and not too far (or the image appears wavy). And if you hold the lens MUCH too far from the object, the image will appear upside down.
Most people don't understand 'focal length' and so when they see a '3' (for some reason eyeglasses are often marked like this) they think it means "3X magnification" when it really means "three inch Focal length". Matters are made worse by the fact that many manufacturers are 'approximate' in their calculations, you can measure the working distance of a 1" magnifier and find it is nearer to 2".
So what is the relationship between focal length (working distance) and magnification? Here is the way I used to calculate it.
you take a 'normal' working distance for reading to be 14", then
a 7" magnifier brings you twice as close = 2X magnification. This
'14 inch rule" is what I used in my catalogue to calculate magnification
up until 2011, and the arithmetic works out like this:
'14 inch rule" is the way I used to calculate it; it is also the
way our manufacturer of watchmakers eyeglasses calculates it, the numbers
convert nicely from inches into more-or-less whole numbers for 'magnification',
as you see from the chart above.
THE 10 INCH RULE
I discovered that according to the almighty Wikipedia the 'normal' working
distance for a lens is 10 inches. This is rather neat because (as you
will see if you read the extra-technical stuff below) 10 inches is about
25cm, and 25cm X4 = 1 meter (near enough), and physicists use 1 meter
as the definition of 'standard' focal length (not very practicable as
a 'working distance')...but don't worry about that, all you need to
know is - the way I calculate magnification now falls in line with the
'official' method you will find online, like this:
These numbers aren't as good as the old "14 inch rule". For instance, both a 3½ inch and a 4 inch lens have a magnification of about 3X. And both a 5 inch and a 6 inch lens both have a magnification of about 2X. And I get customers who think I'm being evasive when I describe two eyeglasses as being, "about the same magnification".
If you would like to try out different focal lengths and magnifications to see how they convert (using this "10 inch rule"), go to my conversion program, click here (it's an Excel file, so you might have to select OPEN).
WHAT DO OPTICIANS AND SCIENTISTS SAY?
This entire system of magnification being "how many times bigger than normal" (or "X magnification") mystifies opticians. What is 'normal'? It varies from person to person. For an optician, a lens has a focal length - a number that can be calculated, not a 'magnification' relative to 'normal'. If you really want a definition of 'normal' you should use the standard distance (focal length) used by physicists: 1 meter. But by this definition you need awfully long arms to hold a 'normal' lens in one hand and a book one meter way in the other hand.
Also, the human eye often requires more than 'just a bit of help with magnification'. That is why you go to an optician - because he has spent years studying optics rather than reading an entry in Wikipedia. I am not an optician and my knowledge of the maths of optics is shamefully poor. I will, however, attempt to guide you through the mysteries of magnification in the following few paragraphs. It is a bit technical, so you may prefer to skip it go straight to 'CONCLUSION' (scroll down for magnifier recommendations).
The following calculations apply to simple lenses, including all jewellers loupes. The following does not apply to 'surgeons' magnifiers which are made of two small telescopes or to full-size microsopes.
FOCAL LENGTH, DIOPTRES AND MAGNIFICATION
"Working distance" is the same as focal length.
The focal length is the distance you hold the lens from the object that gives the most magnification and the clearest image; it is also the point at which a distant bright object (e.g. the sun) makes the smallest image (e.g. to make a fire using the sun); it is also the distance at which you can project a bright scene onto a surface (stand in a dimly-lit hallway and project the image of a bright window onto the wall). Try it with any magnifier, the distance from the lens to the object will be the same with each of the above experiments, this is the focal length of the lens. In practical terms we can also describe this as, "the [ideal] working distance."
The dioptre is the measurement that opticians and lens-makers use, it is more reliable than defining magnification as "how much larger than normal an item appears". This is because "normal" varies from person to person (there is no rule that says you have to hold a book ten inches from your eyes!).
'Dioptre' is the reciprocal of the focal length. To write this as a formula, call the magnification M (if you prefer you may say P for power rather than M for magnification...but let's keep things simple) and the focal length f (in meters not inches) which gives: M = 1 / f.
But this 'magnification' is based on the physicist's 'standard' focal length of 1 meter. If you assume 'normal' working distance for a human holding a magnifier to be a quarter of a meter (about ten inches*) then you must divide by four. The formula for converting dioptre to magnification is therefore M = D / 4. * this is not because there is anything special about 10 inches, merely that it works nicely as a number, because 10 inches is almost 250mm = 0.25m, which is why we divide by four. This is one of two accepted formulae for calculating magnification.
The above formula
works beautifully for small powerful magnifiers such as jewellers loupes
and small readers. For instance, for a magnifier with a focal length
of 30mm: 1 / 0.03m / 4 = X8.33 magnification. But this formula is based
on two assumptions:
But this doesn't work for large lenses with long focal lenses. For instance, if we apply the formula to a large reading magnifier with a focal length of 500mm we get 1 / 0.5m / 4 = X0.5 magnification. Oh dear, that can't be right, it looks as if it reduces rather than magnifies. In a sense, this is true, if you place an object 500mm from the lens and hold the lens against your eye, it won't magnify at all. What you must do is move the object closer than 500mm from the magnifier (the magnification will be less) then move your eye away from the magnifier. Your eyes are no longer looking into the distance (infinity) but are focusing closer.
To allow for this there is another accepted formula for calculating magnification: D / 4 + 1.
Applying this to our magnifier with a 500mm focal length, we now get 1 / 0.5m / 4 + 1 = magnification X1.5, which is more plausible.
All of these figures are approximate, and there are many reasons for this.
Firstly, it depends which formula you use (see above). Secondly, if the result looks clumsy (e.g. a magnification of X8.333) the supplier will round it up or down. Thirdly, how much closer than your 'normal' reading distance an object appears depends on what is 'normal' for you. Fourthly, if you use the "ten inch rule" (see explanation above, and also my magnification calculator) instead of the formula, you get slightly different figures because ten inches isn't exactly 250mm. Fifthly, even when you go to the trouble to measure the focal length and calculate the magnification, you will often find that what is printed on a magnifier is simply wrong.
If you think this is all a little confusing, it is. In fact, it's very confusing. For instance, if you place the object too close to the lens (less than its focal distance) the magnification will be less, and if you hold your eye away from the lens, the magnification will appear to be more.
in magnifiers consistently used the first formula, above (D / 4). As
a result, most of their magnifications were listed as being less than
one, indicating that they made everything appear smaller rather than
larger. Then they re-printed their brochure, listing magnifications
consistent with the second formula, D / 4 +1.
IF YOU WEAR SPECTACLES
If you wear spectacles, should you keep them on whilst using a magnifier?
When using a large magnifier (e.g. for reading) the answer is: yes. I assume, here, that you need a magnifier because the print / map / mark is exceptionally small and you need that extra help in addition to your spectacles.
When using a small magnifier (e.g. a jeweller's loupe or watchmaker's eyeglass): do whichever is the most comfortable, but you must keep the magnifier as close to your eye as possible.
The only time you may wish to think about whether to keep your spectacles on or take them off is if you are wearing a magnifier over your head (e.g. a binocular headband magnifier), they can be used with or without spectacles, as follows:
If you are short-sighted (you have difficulty in seeing far objects, your spectacle lens prescription has a power beginning 'minus' ) you will notice that when using the magnifier without your spectacles the working distance is less than marked on the magnifier. If you are very short-sighted you will also notice that without a magnifier you can focus on very close objects - you have magnifying eyes for close objects (the only drawback being that you can't focus on far objects). The consequence is that with a binocular magnifier you may choose between two magnifications, one (weaker / further away) when you wear the magnifier over your distance spectacles and one (closer / stronger) when you wear the magnifier without spectacles, whichever you find the most comfortable.
If you are long-sighted (you have difficulty in seeing near objects, your spectacle lens prescription has a power beginning "plus") you will notice that when using the magnifier without your spectacles, the working distance is more than stated on the magnifier. If you are very long-sighted you will also notice that a low-power magnifier doesn't actually magnify at all, it merely brings close objects into focus at a 'normal' viewing (e.g. reading) distance, which is exactly what your reading spectacles do: they are low-power magnifiers. The consequence is that with a binocular magnifier you may choose between two magnifications, one (stronger / closer) when you wear the magnifier over your spectacles and one (weaker / further away) when you wear the magnifier without spectacles, whichever you find the most comfortable.
VIDEO MAGNIFIERS (for the partially sighted)
- GUIDE TO MAGNIFIATION
When choosing a lens magnifier, as a guide to magnification (for reading text): 1.2X to 2X is what you should be choosing as 'just a bit of help' when reading (especially if reading maps in a car, when you need a large lens to glance down at the map then glance up at the road signs). If your eye sight is very bad, go for 3X to 5X. But once you get to about 5X you really are only able to see one or two words at a time, eveb with the best lens made for the partially sighted. HOWEVER, there are many partially sighted people who need greater magnification, and the solution is to use a screen (monitor) and video camera. You can then make the text as large as you like, until one word fits the entire handheld device (or a 22" screen!).
- TYPES, PRICES (Summary)
The handheld versions are made out of a tiny video camera on the back of a screen. They vary from the size of a small mobile phone to the size of a postcard, prices from £175.00 to £840.00.
The desk versions come in two forms, camera-only or complete reader. A camera-only has an adjustable arm on a stand (you plug it into your computer monitor, laptop or TV). A complete reader includes the monitor and a lighting system.
In the next few weeks we will be 'trialing' many models, and by early September (2012) will have an entire article explaining the pros and cons of video magnifiers - watch this space.
If you are buying by mail I hope the above will help you make your choice, and as with any item bought from us by mail unseen, you can return for exchange, credit or refund (your choice) providing it is returned in its original condition within fourteen days.
If you are visiting the QUICKTEST stand at a fair, simply try them out. Bring with you something familiar, e.g. a coin or stamp if you are a coin or stamp dealer, a book, photograph, print etc. If you have an existing magnifier and wish to upgrade, bring it with you so that you can compare - we will not be offended, if your existing magnifier is better than anything we have, we will be eager to know where you got it!
We help thousands of people choose magnifiers, we really do understand magnifiers. However, we are not opticians, we cannot comment on your spectacle prescription; we are not doctors, we cannot comment on your eye condition; you must consult an optician or doctor if you have concerns about your eyes.
For the partially-sighted - you may wish to read a separate article about magnifiers for the visually impaired, or to see the best magnifiers for the visually impaired click here. These include video magnifiers. If you are registered blind or partially-sighted. fill in our form (you can return it by post or by email) so that you don't have to pay VAT . If you do not consider yourself 'partially-sighted', keep reading.
For reading books, papers, magazines, directories, recipes, and maps in daylight see any of our readers (there are dozens of them, under six categories). The simplest are traditional magnifiers with handles. We also have flat plastic-sheat Fresnel lenses, some are small (the size of a credit card), some are large (page-size) but these are never as good as 'traditional' magnifiers in quality. If you don't like the idea of holding a magnifier for long periods, the magnifiers a stands are good (some have lights and plug into the mains, some do not), or if you don't mind wearing a magnifier around your head there are various head-worn magnifiers. A compromise between 'handheld' and 'hands-free' are the magnifiers you rest on the page (you slide them along the page), the bar magnifier is low magnification but excellent for dyslexics (it stops the eye wandering) or, at the very bottom of the same page, the dome magnifier is a good choice (and there are very powerful versions for the partially-sighted)
For map reading in the car (including at night time) any of the large illuminated readers are good. I keep, in my car the largest hand magnifier - it is large enough to cover most of a page, enabling me to keep glancing up at the road signs and then back at the magnifier and not lose my place on the map (there is a similar one with a light). There are also four sizes of illuminated Lumagny, a small-ish and very 'standard' magnifier at about half the price you will see in car accessory shops, a good 'budget' magnifier. Incidentally, I'm not suggesting that you should be map reading and driving at the same time!
For carrying in the pocket for occasional reading, e.g. the labels on supermarket products, the 'small print' on forms, those horrible photo-reduced instruction sheets. The credit-card size Fresnel (flat) magnifier is good, though not particularly high in magnification or clear in quality. For a good selection of pocket-size magnifiers see our small folding magnifiers. I would also recommend the larger of the illuminated magnifiers (the smaller, more powerful, versions are for jewellers and diamond dealers).
For sewing, embroidery and other flat-ish craft work any of the hands-free magnifiers are good. If you need extra magnification you could even try a head-worn magnifier, from the simple type to the expensive surgeon's type, though you might think the larger versions are a bit 'over the top'. There are some good magnifiers on stands, some small and some large (and if you have space, the larger illuminated magnifiers are just amazing). My colleague has the one on a stand set up by the lathe in the workshop.
For model-making, fly-tying, clock repairing and other engineering jobs including lathe work the stand magnifiers listed above are good, but you might also consider a head-worn magnifier, from the simple headband magnifier to the expensive surgeon's type magnifier.
For particularly close work such as watch repairing the head-worn magnifiers, above, are good, but you could get away with the simpler magnifiers that clips to spectacles or which you hold in the eye (watchmakers eyeglass).
Any of the above would suffice for PCB inspection, but it depends on whether you will using it for a few minutes a week (you may not consider it worthwhile spending more than £5.00 or £10.00 on any simple magnifier) or a few hours per day - consider the Mantis stereo microscope, at £1440.00.
For stamps & coins, prints & postcards, fabrics etc the powerful stand magnifiers are good (traditionally, the linen prover is for measuring the threads-per-inch), or you could even use a pocket microscope - these are all for use on flat objects. Alternatively, any loupe (with or without a light) or eyeglass. For prolonged use on in a laboratory use a large mains-powered illuminated magnifier; or for the ultimate magnifier, a Mantis...or you might like to see a selection of secondhand microscopes.
For jewellery, gemstones and very small marks on antiques, also insects and plant samples choose any jewellers loupe (with or without a light) or an eyeglass. Traditionally 10X magnification is used by gem and diamond dealers, a magnifier will be your most important tool, buy the best you can afford. For larger marks (e.g. on porcelain and furniture) any folding magnifier should suffice.
Decorative magnifiers / gifts, I don't really sell magnifiers 'just for decoration', but you could try the pendant magnifier (regular line). Spare parts, I have many bulbs, pouches, chains etc for magnifiers.
QUICKTEST, Watford, WD18 8PH, Tel. 01923 220206, email info(at)quicktest.co.uk