Magnification equipment is essential for anyone working with precision assembly, inspection, or design, and for low magnification, bench magnifiers are the number one option.
The reason why bench magnifiers are so popular is that they give users increased magnification without needing to advance to using a stereo microscope. Magnification on bench magnifiers is expressed as ‘dioptre’. Dioptre is a term used to identify the refractive capacity of a lens, where each dioptre increases magnification by 25% above the original size. For example, a 4-dioptre lens equals a 100% magnification increase above the original size.
Most bench magnifiers are available in 3,0, 3,5 and 5,0 dioptre models, which equate to 1,75x, 1,88x, and 2,25x magnification. To increase magnification further, secondary lenses are available, which can increase magnification to 10 dioptre (3,5x). It should be noted that increasing magnification will however reduce working distance and field of view.
Field of view
The field of view is the area of the magnified subject that is in focus under the magnifier lens. Focal length and working distance refer to the distance from the centre of the lens to the subject that is in focus. Depth of focus is the distance an object can be moved and remain in focus.
An important consideration is that as magnification increases the field of view, focal length/working distance decreases. Since bench magnifiers are designed for tasks requiring a low magnification, the typical focal length/working distance for 3D and 5D systems can range from 330 to 200 mm.
Lens quality
There are two types of glass used in optics, Crown glass and Flint glass. Crown glass is clearer due to its high Abbe value, which means there is less chromatic distortion, giving the user the best view possible. Crown glass also offers superior resolution and image clarity.
Illumination
Proper lighting is equally as important as magnification when it comes to attaining optimum viewing conditions. Many workplaces have indirect light or lighting that may create shadows on the subject. Illuminated bench magnifiers compensate for poor light conditions, giving the user a better viewing experience. Using illumination that will not alter the viewing colour of the subject should be considered.
LEDs have become the industry standard when it comes to illumination. They have an incredibly long lifespan (25 years under normal use) and offer excellent colour rendition, measured by the Colour Rendition Index (CRI). This ranges from 0 to 100, with 100 signifying the most exact, natural colour. Bench magnifiers that have a CRI rating of 80 and above are considered excellent for accurate colour rendering.
Illumination is also measured by correlated colour temperature (CCT), measured in Kelvin (K).The ideal illumination colour for a bench magnifier measures between 4000 and 5000 K. This is considered natural white light and is best to replicate daylight conditions.
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