|
|
|
HOW TO CHOOSE A MAGNIFIER To go straight to our products to see the huge selection of magnifiers, click here To jump to the bottom of this page and see our recommendations, click here
CONTENTS OF THIS ARTICLE: All about Magnification, Names, How to use a Magnifier, Lighting, The Rules and the Materials, Magnification and Working Distance, More Technical Stuff, Quality and Price, Conclusion. About focal Length, Dioptres and Magnification,
OTHER ARTICLES 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. Incidentally,
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 plastic handles (I call them Readers), some fold or slide into cases (I call them 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 jeweller's loupe (pronounced 'loop') is a small folding magnifier (from 12mm to 21mm diameter) of high magnification (usually 10X or 20X) which folds into a metal or plastic case. A watchmaker's eyeglass is a cone of plastic, you hold the open end in your eye (it takes practice!). The IDEA of a watchmaker's eyeglass is that there's enough working distance (space between the lens and the object) to repair the watch, which means that 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 £95.00 (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 [and scroll down] 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 a the cheapest largest reading magnifier because they don't like to spend money, some hobbyists will spend £89.00 on a Zeiss 10X20 loupe simply 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, bright ceiling lights or a table light close to the object . If you are a trader buying at pre-dawn fairs or viewing in dimly-lit auction halls, or if you are partially-sighted you may require very bright light. The light must be between the magnifier and the object, do not shine the light at the magnifier, you will merely be blinded by reflections. Magnifier 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 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 [and scroll down] or clip-to-spectacles [and scroll down] or plug into the mains [and scroll down]. 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 and wonder why 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 [and scroll down] at £89.00) are made of plastic...though 'plastic' sounds too downmarket 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 nature, there is no way round 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 (I call them Surgeons' Magnifiers); a high quality low-power microscope (I also have various models secondhand); a scanner that connects to a computer or TV to enlarge print in a book or newspaper. You will notice that we sell two new pocket microscopes each with a magnification of 30X, and a large microscope with magnifications (selectable) of 2X, 4X and 6X. And you might notice that the 30X microscopes sell for £5.00 and £7.50 and the 2X, 4X, 6X microscope sells for £1500.00. 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 and you can see for yourself by trying them out at the QUICKTEST stand at the antiques fairs. Or if you buy by mail and the magnifier turns out to be unsuitable, you can return it. 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 might never know just how awful they are! TECHNICAL STUFF: MAGNIFICATION AND WORKING DISTANCE Some magnifiers are marked with the magnification, some are marked with the focal length (working distance) in inches. The focal length 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 wobbly). 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 calculate it. If
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 use in my catalogue to calculate magnification: 3.5 inches = 4X magnification. 3 inches = 4.5X magnification. 2.5 inches = 5.5X magnification. 2 inches = 7X magnification. 1.5 inches = 9X magnification (but our eyeglasses are closer to 8X). This system mystifies opticians because focal length is a physical constant that can be calculated, there isn't really such a thing as a 'normal' working distance, it varies from person to person. Opticians use a different system, the dioptre. +4.00D is (for a normal-sighted person) 2X magnification NOT, as you will see in the 'gadget' mail order catalogues 4X magnification. Furthermore, +4.00D is the strongest reading spectacle that an be legally sold 'over-the-counter', if you need stronger you must go to an optician (this rule doesn't apply to handheld magnifiers, merely to the type of head-worn magnifier we call "reading spectacles"). The next two sections contain more technical information, feel free to skip them! FOCAL LENGTH, DIOPTRES AND MAGNIFICATION 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, e.g. 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." 'Dioptre' is the reciprocal of the focal length. To write this as a formula, we call the power (magnification) P and the focal length f, (in metres not inches) which gives us: P = 1 / f. Those who are good at algebra can now work out the formula to convert dioptre to power (magnification): P = D / 4 + 1. So, for instance, a typical lens you clip to the front of spectacles will be marked +4.00D giving a a power (magnification) of 4 / 4 + 1 = 2X (NOT "4X magnification" as most mail order catalogues state). Zeiss loupes are marked in dioptres, their +36D lens is 36 / 4 + 1 = 10X. The focal length of a magnifier does not have to be less than 14 inches (see above), it can be more. So, for instance, we have a 125mm diameter reading magnifier which is marked (on the packaging) "2.5X Magnification" - and so I advertise it as just that: 2.5X magnification. But this only applies when it is used at its focal length which is 24 inches. It is not possible to hold a book in one hand and the magnifier in the other and keep the two 24 inches apart because human arms aren't that long; you will use this closer than 24 inches and the magnification will be less than 2.5X.* But I list this as "2.5X magnification" because people believe what is printed on packaging, they will not believe me, and very few people with bother to read this explanation! * if you try out the above calculations you will find that a 24 inch magnifier isn't as powerful as 2.5X (even when used at its focal length) but if customers knew this they wouldn't buy it, they would think it was 'not strong enough' - whereas in practice it is one of the best reading magnifiers we have. 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 (eg 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. 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 any item that is unsuitable 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 reading books, papers, magazines, directories, recipes, and maps in daylight see any of our readers. For large-area magnifiers try the flat Fresnel lenses, some are small (the size of a credit card) and some are large (page-size) but these are not as good as 'traditional' magnifiers in quality. We have, of course, many traditional magnifiers with handles. If you don't like the idea of holding a magnifier for hours, try a magnifier on a stand. One I particularly like is a large reading magnifier 2X 80X80 on a handle, and the handle can be tilted to rest on the page, AND it has four powerful L.E.D. lights so that the print is always brightly lit no matter how you tilt the lens. For the strongest hands-free magnifiers (though these are more intended for jewellers and engineers) there are various head-worn, magnifiers (some clip to spectacles, some are on a headband). 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 wondering) or, at the very bottom of the same page, the dome magnifier is a good choice For the partially-sighted - to read about these in more detail, click here. Here is a very brief summary. Illuminated. The largest is 2X 80X80, it has four LED lights. More powerful, but small-ish, is the 3X 50X75. With handles (no light). There are two Russian magnifiers, the 5X50 is one of the most powerful but it will only show you 3 or 4 words at a time; the 7X50 is the most powerful but it will only show you 1 or 2 words at a time, and the quality of these lenses is not good, there will be distortion. Best are the Zeiss readers, best lenses, virtually no distortion. The 3X is just about large enough to read a column of print. Rest-on-page. The dome is quite OK, it is cheap and quite powerful, but small, you can't quite see (left to right) an entire newspaper column. THE best for the partially-sighted is the hedgehog, especially designed for the partially-sighted and with many features. Other. If you really do not want to spend time finding the best combination of magnifier + table light at just the right angle, the large professional mains-powered illumated magnifiers are amazing. For an entire page of recommendations (and to read about these magnifiers in more detail) click here. For mapreading in the car (including at night time) any of the illuminated readers will do, my favourite is the 2X 80X80. I also keep, in the 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..but it doesn't have a light. There are also four sizes of illuminated Lumagny magnifiers, to my expert eyes these are not very good quality, but they are 'good value' and are about half the price as the car accessory shops. Incidentally, I'm not suggesting that you should be mapreading 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. 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 [and scroll down] are just amazing. For model-making, watch and clock repairing and other engineering jobs including lathe work, also fly-tying: head-worn are good, from the simple type to the expensive surgeon's type. For particularly close work you should consider a magnifier that clips to spectacles or a watchmakers eyeglass. The larger magnifiers listed above, under sewing, embroidery etc would also be suitable. My colleague has the one on a stand set up by the lathe in the workshop. The ultimate workshop magnifier is the large Mantis stereo microscope. For stamps & coins, prints & postcards, fabrics etc the powerful stand magnifiers are good (traditionally, the 'Linen provers' are 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 lluminated magnifier [and scroll down]; 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 loupe (with or without a light) or 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 |