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January 16, 2013

BEWARE CLAIMS OF 2,000X MAGNIFICATION

False Magnification…. False Advertising or both? Be careful about buying a microscope that advertises 2,000x magnification. 2,000x is double the magnification for which standard light microscopes are designed so 2,000x must be too good to be true – as indeed it is!

Claims of 2,000x are achieved by the simple expedient of adding a set of 20x eyepieces to the standard 10x eyepieces. Magnification is achieved by multiplying the power of the objective lens by the power of the eyepieces. So 20x eyepieces x 100x objective lens = 2,000x total magnification, right?

Well, yes…..and no! Yes, the total magnification of the image increases, but the resolution of the image will degrade to the point where it is useless. This is because those higher power eyepieces push the total magnification above the Maximum Useful Magnification of the microscope. They higher power eyepieces create False or Empty Magnification. This is similar to when you try to zoom in on a slightly blurry pdf on a webpage. The image gets bigger but there is no improvement in resolution.

Maximum useful magnification is approximately equal to the size of the numerical aperture (N.A.) multiplied by 1,000. So, for a microscope with an NA of 1.25, the maximum useful magnification is approximately 1,250x. Anything above this maximum produces false magnification. The additional magnification yields no further useful information or finer resolution of detail. Quite the contrary. You will likely experience severe degradation in resolution. To quote Nikon, “In fact, excessive magnification introduces artifacts, diffraction boundaries and halos into the image that obscure specimen features and complicate the interpretation of visual interpretations”. In other words, the image gets blurry!

That is why all standard light compound microscopes are designed and sold with 10x eyepieces as standard and 100x objective lens as the largest obejective lens. At a 1,000x magnification, you do get higher magnification and improved resolution over, say, 400x, because the total power of magnification does not exceed the maximum useful magnification of the microscope.

Now, with some better quality microscopes you can get away with using 16x eyepieces. 1,600x is not such a stretch from 1,250x when using a microscope with NA 1.25. But 20x or 25x eyepieces? Not only will they not work efficiently but they are likely to frustrate your experience.

Those websites advertising 2000x magnification? False Magnification and false advertising in my opinion.