Different magnifications of objective Lenses

Most compound microscopes have objective lenses, and these objectives are also called interchangeable objectives because the objective lenses have various magnifications, the most common are 4x, 10x, 40x and 100x, usually we also call scanning, low magnification, high power and oil Immersion objectives; Let's get to know how these objectives are used in microscopy

Scanning Objective Lens (4x)

A scanning objective lens provides the lowest magnification power of all objective lenses. 4x is a common magnification for scanning objectives and, when combined with the magnification power of a 10x eyepiece lens, a 4x scanning objective lens gives a total magnification of 40x. The name “scanning” objective lens comes from the fact that they provide observers with about enough magnification for a good overview of the slide, essentially a “scan” of the slide. Some objectives with even lower power are discussed in Specialty Objectives below.

Low Power Objective (10x)

The low power objective lens has more magnification power than the scanning objective lens, and it is one of the most helpful lenses when it comes to observing and analyzing glass slide samples. The total magnification of a low power objective lens combined with a 10x eyepiece lens is 100x magnification, giving you a closer view of the slide than a scanning objective lens without getting too close for general viewing purposes.

High Power Objective Lens (40x)

The high-powered objective lens (also called “high dry” lens) is ideal for observing fine details within a specimen sample. The total magnification of a high-power objective lens combined with a 10x eyepiece is equal to 400x magnification, giving you a very detailed picture of the specimen in your slide.

Oil Immersion Objective Lens (100x)

The oil immersion objective lens provides the most powerful magnification, with a whopping magnification total of 1000x when combined with a 10x eyepiece. But the refractive index of air and your glass slide are slightly different, so a special immersion oil must be used to help bridge the gap. Without adding a drop of immersion oil, the oil immersion objective lens will not function correctly, the specimen will appear blurry, and you will not achieve an ideal magnification or resolution. Oil immersion lenses are also available from some manufacturers in lower magnifications, and provide higher resolution than their "high dry" counterparts.

Specialty Objective Lenses (2x, 50x Oil, 60x and 100x Dry)

There are several other objective lens magnifications available with utility for particular applications. The 2x objective, widely used in pathology, has only ½ the magnification of a 4x scanning lens, thus providing a better overview of the sample on the slide. The 50x oil immersion objective, often used in place of the 40x objective, is used as a gold standard for observing blood smears. The 60x objective, often available in either dry or oil immersion, provides 50% greater magnification than a 40x lens. The 60x dry is sometimes chosen over a 100x oil immersion lens for higher magnification without the need to use immersion oil.  Finally the 100x dry objective doesn’t need immersion oil to deliver high magnification (still 1000x when combined with 10x eyepieces). However, the numerical aperture (an indication of resolving power of an objective) of a 100x dry objective is much lower than that of a 100x oil immersion objective and, as a result, the ability of the lens to resolve fine details in the specimen is much lower, too.

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