Man holding an open book in front of his face with both hands


Did You Know…

…why We Get Closer to Something when We Cannot See It Clearly?

To be able to perceive two dots as separate, the observer must be able to recognize the space between them. In small print, the two dots in a German umlaut (“ü”) are closer together than two stars in the night sky. The perceived distance between two dots also plays a key role. And it all depends on the viewing angle from which the observer is looking at them. A human eye with normal vision can resolve a viewing angle of 1/60 of a degree.

In other words, if you want to see two dots clearly on a sheet of paper, you can simply move closer, thereby increasing the viewing angle, or you can bring two stars closer to you by using a pair of binoculars to increase the viewing angle in a similar fashion. If this is not sufficient, you have to get a magnifying glass or even a microscope. However, “moving closer” is not necessarily helpful in the latter case, as another resolution limit applies,as discovered by Ernst Abbe 138 years ago. It states that the resolution is also dependent on the wavelength of the light.

Abbe’s resolution limit for optical microscopes at around 200 nanometers was long considered to be insurmountable. That is, until optical tricks were used to get around it. Through the skilled use of fluorescence, it is now possible to resolve much smaller structures – down to 20 nanometers. In order to read the fine print, however, it is usually enough to simply move closer.

22 February 2011