If you are purchasing a magnifier for the first time, we recommend you see your eye doctor to determine the strength of magnification you require. We then encourage you to come into the "EYE-dea" Shop where a specialist can assist you with your purchase. You CANNOT be fitted for a magnifier with dilated eyes.
Diopter refers to the curvature of a lens. As the diopter increases, the lens becomes thicker and the curvature greater. As the curvature increases, light rays are redirected to fill a greater portion of the viewer's retina which makes the object look bigger.
Power refers to how much larger an object is made to look through a magnifying lens. Power is typically indicated by an "X" such as 2X or 4X. The formula for computing power is as follows:
Therefore, an 8 Diopter lens makes an object look 2 times bigger, over and above what the unaided eye already sees.
Focal length is the distance from the center of a lens to the point where the light rays converge and the object is in optimal focus (focal point). This is also known as the "working distance" of the lens. Focal length is important when the task requires using tools with the object being viewed. Because focal length decreases as power increases, there is less room to perform work on an object under higher power lenses.
The field of view is the size of the magnified area under the lens that is in focus. The field of view decreases as power, or magnification, increases. More powerful lenses make small details look big, but less of the total object is visible. There is a trade-off for the viewer who must decide between the size of the field of view and amount of magnification (see below).
Proper lighting is equally important as magnification in achieving a good viewing situation. A magnifying lens would be useless in the dark, so increasing light levels results in better vision. In fact, the better the quality of light used with a magnifying lens, the less power is needed. When less magnification is required, the user has a bigger field of view and working distance under the lens. Therefore, the quality of light should be closely evaluated when choosing an illuminated magnifying lamp.
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