When you are looking at the variety of magnifying floor lamps on offer you may find the terms used for the magnification a little confusing. Comparing two of them might have you looking at one that describes how many Diopters and another one what magnification they have. There is a magnification table here should you just want to look up how they compare. This is an explanation of what these terms mean together with a few points that may help you to remember the difference between them.
With magnification it is all to do with how the light is being bent within the lens of your magnifying floor lamp. This bending of light by the glass lens helps you see text, images or objects larger than normal. This makes it easier on the eyes and helping you see more details than you would with the naked eye. If you are looking at anything closely for too long you will notice how uncomfortable it can be as the muscles in the eye get tired, so using a magnifier of any description helps ease this.
Instead of doing the conversions in on your calculator or in your head most of the useful ones exist in this Magnification Chart.
You will find much more in depth information on this subject at http://en.wikipedia.org/wiki/Magnifying_glass.
The focal length of a lens is the distance where parallel beams of light coming from one side will converge to a point on the other side. Essentially what it means is that the shorter the focal length the higher the lens will magnify. For further technical details see http://en.wikipedia.org/wiki/Focal_length. You will often see this measurement in inches.
From Focal Length (in inches) to Diopter – Divide the number 39.37 by the Focal Length. If you are without a calculator use 40, it will work around about right. Diopters are usually given to the nearest single 0.5.
Example - For a magnifying lens that has a focal length of 8 inches then the lens has a diopter of 5. Using (39.37/8=4.92) and rounding to the nearest 0.5.
From Focal Length (in inches) to Magnification Power – Divide the number 9.84 by the Focal Length (in inches). If you are without a calculator just divide it by 10. The Magnification Power is then rounded to the nearest 0.25.
Example - For a magnifying lens that has a Focal Length of 10 inches then the Magnification Power is 1x. Using (9.84/10=0.98) and rounding to the nearest 0.25.
From Focal Length (in inches) to Total Magnification Power – Divide the number 9.84 by the Focal Length (in inches) and then add 1 to the result. If you are without a calculator just divide 10 by it. Then round to the nearest 0.25.
Example - For a magnifying lens that has a Focal Length of 5 inches then the Total Magnification Power is 3x. Using (9.84/5=1.97+1=2.97) and rounding to the nearest 0.25.
Diopter is less commonly spelt as dioptre. This is a unit of measurement for showing the magnification of the magnifying floor lamp. The higher the value of the diopter, the more magnification the lens has. For more technical information on diopter see http://en.wikipedia.org/wiki/Diopter. Its measurement is based on the SI Unit of metres, which in Imperial measure is 39.37 inches, so in calculations you often get long values but rounding to the nearest number 40 is usually fine.
From Diopter to Focal Length (in inches) – Divide 39.37 by Diopter, though if you are without a calculator use 40, it’s close enough.
Example - For a magnifying floor lamp that is 3 Diopter then the Focal Length of its lens will be about 13 inches. Using [39.37/3=13.12] and rounding to the nearest inch.
From Diopter to Magnification Power – Divide Diopter by 4.
Example – For a magnifying floor lamp that is 8 Diopter then the Magnification Power of its lens will be about 3x. Using [8/4=2].
From Diopter to Total Magnification Power – Divide Diopter by 4 and then add 1
Example - For a magnifying floor lamp that is 5 Diopter then the Total Power of its lens will be about 2.25x. Using [5/4=1.25+1=2.25].
Is a number usually followed by ‘x’ that shows how much bigger an object looks where viewing through the magnifying floor lamp lens. If an object is 100% bigger the magnification power will be given as 1x. Even though this is called ‘magnification power’ it is often mistaken for ‘total power’, the definition of that follows and both of these values gets mixed up. So if you see a magnifying floor lamp of 2x this is usually meant to be total power and not its magnification power. Magnification Power is usually rounded to the nearest 0.25.
From Magnification Power to Focal Length (in inches) – Divide the number 9.84 by Magnification Power. Without a calculator then simply use 10.
Example – For a magnifying lens that has a Magnification Power of 1.5x then its Focal Length is about 6.6 inches. Using [9.84/1.5=6.56] and rounding.
From Magnification Power to Diopter – Multiply by 4
Example – For a magnifying lens that has a Magnification Power of 1.25x then its Diopter is 5. Using [1.24*4].
From Magnification Power to Total Magnification Power – Just add 1
Example – For a magnifying lens that has a Magnification Power of 0.75x then the magnifying floor lamp will have a Total Magnification Power of 1.75x. Using [0.75+1=1.75].
Total Magnification Power or Total Power
This is the most commonly used way of describing the magnification between that and the above magnification power. It is simply the Magnification Power + 1. The reason this term is used more often is because it is simper to understand but many people mistake one for the other. If an object that is 5 inches wide is viewed through a magnifying floor lamp lens and appears as a 10 inch object then the Total Power of the lens is 2x. The Total Power is then rounded to the nearest 0.25.
From Total Magnification Power to Focal Length (in inches) – Subtract 1 from the Total Magnification Power then divide the number 9.84 by the result. Or, if doing it in your head use 10.
Example - For a magnifying floor lamp that has a Total Power of 3x then the Focal Length of its lens will be about 4.9 inches. Using [9.84/(3-1)=4.92] and rounding.
From Total Magnification Power to Diopter – Subtract 1 from the Total Magnification Power then multiply the result by 4
Example - For a magnifying floor lamp that has a Total Power of 2x then the Diopter of its lens is 4. Using [(2-1)*4=4].
From Total Magnification Power to Magnification Power – Subtract 1
Example - For a magnifying floor lamp that has a Total Power of 3x then then its lens will have a Magnification Power of 2x. Using [(3-1)=2].