How to choose the right magnifying lamp - What does Dioptre mean? Is it the same as Magnification? What is the best lighting?
Many situations benefit from seeing something larger and clearer, including:
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A hands free magnifying lamp is often the best all purpose solution. These come in many shapes and sizes; strengths and prices. The biggest, the most powerful, the most expensive, are not necessarily the best options for everyone. But choosing the right magnification for your needs can be confusing.
Without being too technical, I thought a brief overview and clarification of the main terms used might be a helpful guide. Some ads rate magnifier lamps in Dioptres, some in power, some in %, some in X. So what do they all mean; well the first thing to understand is that if a lamp is described as 3 Dioptres, it does NOT mean that it magnifies 3 times (3X) - see chart below.
Dioptre: is a unit of optical power of a lens equal to the reciprocal of the focal length measured in metres. Or put simply, it refers to the curvature of the lens. As the curvature increases, the lens becomes thicker, the Dioptre increases and provides higher magnification.
Power: refers to how much larger an object appears, typically expressed as x, eg: 2X or 4X etc. Dividing Dioptres by 4 gives the power of a lens, eg: 3 Dioptre is 0.75X or 75% increase in size.
Magnification: another way of expressing the power but includes the original as 1 or 100%. Dividing the Dioptres by 4 and adding 1 gives the magnification, eg: 3 Dioptre is 1.75X or 175% of the original.
Focal length: basically this is the working distance between the object and the lens. The higher the magnification, the nearer the object needs to be to the lens.
Lighting: good quality lighting, correctly positioned, is essential for any close work. Magnifier lamps of course have integral lights shining onto the object away from your eyes. If accurate colour definition is important, standard warm white bulbs or tubes (rated at 2700Kelvin) have a yellowy tint and will distort colours. A cleaner, more neutral shade is more suitable, from cool white (4000k) to daylight (6400k). Even if you don't need true colour definition, cool white will give a cleaner light and reduce eye strain; daylight is even better but usually more expensive.
General: to avoid eye strain and a stiff neck when using a magnifier lamp, arrange your chair, table and the lamp in a convenient and comfortable position. Use both eyes which should be about 8-10 inches from the lens, then move the object closer or further from the lens until the image is clear. Wear spectacles if you normally do.
Tips: when choosing a magnifier lamp, bear in mind that the more you magnify an object, the less of it you will see.
Finally: consider carefully the specifications to make sure the magnifier lamp you are buying suits your needs. If full details are not given - ASK. Here at UKRDESIGN.CO.UK, we welcome questions from customers as we like you to know exactly what you are buying - and from our point of view it avoids returns - so we are all happy.
(Sorry it is not possible to include a proper chart in an eBay Guide.)
Dioptre = Magnification = % larger than object ~ approx focal length:
3d = 1.75x = 175% ~ 13"
5d = 2.25x = 225% ~ 10"
8d = 3.00x = 300% ~ 6"
12d = 4.00x = 400% ~ 3.5"
Bear in mind these are based on 'typical' eyes so the actual magnification achieved will depend on your own eyesight.
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