Many branches of science, such as microbiology, rely on microscopes to provide visualization of very small specimens. Because even tiny specimens vary in size by several orders of magnitude, microscopes need to have various magnification options available; these are indicated by colored bands around the objective lens column. In addition, bands may also indicate immersion media.
The colored band that is closest to the mounting thread and nose piece indicates the magnification strength of that objective lens. This band can be distinguished from the immersion media band because it is thicker and higher up on the lens column. The magnification strength is usually printed in numbers as well, but colors are useful because they can be viewed much more quickly than magnification numbers can be read.
Magnification Color Code
Microscope magnification strengths are typically written as a number followed by the letter "x." For example, if a lens makes something look 100 times as large as it really is, that lens's magnification strength is 100x. The most commonly used magnifications and corresponding band colors are as follows: black means 1-1.5x, brown means 2x or 2.5x, red means 4x or 5x, yellow means 10x, green means 16x or 20x, turquoise means 25x or 32x, light blue means 40x or 50x, bright blue means 60x or 63x and white or off-white means 100-250x.
Some microscopes only have one colored band, in which case it indicates magnification as described above. However, many microscopes have a second band that is thinner and lower down than the first. This bottom band indicates the immersion medium of that lens.
Immersion Media Color Codes
Most specimens are viewed against air, but certain specific specimens are more easily seen when contrasted against water, oil or glycerin. A white band indicates a water immersion, a black band indicates an oil immersion and an orange band indicates a glycerin immersion. Red indicates a special, or "other," immersion.