Why Is 100x Objective Called A Wet Objective

Why is 100x Objective Called a Wet Objective?

Immersion oil microscopy is an essential technique for high-powered microscopy when you wish to achieve the highest magnification.

Due to the manufacturing limitations, there are several discrepancies with a higher-powered lens or microscope. In this section, we will discuss the importance of immersion oils.

Why is immersion microscopy so important?

When rays of light pass from material to the other, they bend. This phenomenon is called refraction.

The space between the specimen slide and the objective lens is responsible for this occurrence. As the light scatters, most of it is lost.

Air’s refractive index is 1.0, and that of glass is 1.5. when light passes between the two media, it does not escape refraction.

When different wavelengths bend, the magnification increases. This is not a good aspect as the sharpness of the image is lost.

When you use a low-power objective, the refraction is gladly not as apparent. But as soon as you employ a high-powered objective, the refraction makes the viewing redundant.

Reducing the amount of light refraction, the viewing becomes better. As you save more light, you are also ensuring crisp looking images.

When you place an immersion oil, the air gap does not remain empty. This occurs because the refractive index of the two media becomes closer to each other.

When is an immersion oil applicable in microscopy?

Here are the most applicable situations when using immersion oil. It is important to note that immersion oils are not suitable in all scenarios.

  • You need to procure an immersion lens for using immersion oils. If it’s an immersion lens, it will be marked as HI on its body.
  • Immersion oils are best for viewing inanimate or dead matter. The specimen should not be thicker than a few micrometres.
  • If you need equipment, you can view tiny motile protists. However, for the best immersion oil microscopy, you need inanimate objects that are preferred.
  • When you are viewing bacterial strands or detailed specimens, you need immersion oils. You also need the same for a crisp image at 1000x.

The 100x objective lens

A wet objective lens is simply a term used when you are using a liquid to cover the air gap. The air gap in this context refers to the space between the Objective and the slide.

The liquid medium in question is the oil immersion. The oil-immersion acts as a bridge or the light path for the incoming rays of light.

When you use oil immersion, you are enhancing to significant aspects of microscopy. These two factors include the aperture in units and the resolution of the image.

It is for this reason oil immersion is only suitable for high-powered microscopy. You need to use oils curated for microscopy to keep your equipment safe.

The immersion oil must have the same refractive index as the objective lens. Your microscope’s manufacturer is typically specified what type of oil is best.

The best kinds of oils for oil immersion microscopy is Type A and Type B oil. Type A is low viscous oil, whereas type B is high viscous oil.

Application of immersion oils

You can use an applicator rod that has a tapered end for easy application. You can also measure the amount of oil using the tipped rod.

You must tip-off the neck of the rod. This prevents the oil from creeping outside of the bottle. This eliminates dust and the oil from getting to your fingers.

While applying the oil to the microscope, make sure you remove the air bubbles. The bubbles, if caught in the immersion, will hinder the clarity of the image.

You can avoid this problem with much ease. Make sure that the drop is in contact with the slide or the condenser lens.

The oil should flow from the application. If you dab the immersion oil on to the surface, that will create more bubbles.

Make sure you keep the drop of oil at a small height from the surface. After applying the oil, raise the slide to make contact with the surface slowly.

The correct procedure for oiling the Objective is by putting the drop of oil on the slide and lowering it to the Objective. You can also rotate the Objective, so it makes contact with the oil.

You don’t need to reoil as often once you oil the lens properly. You should remove the drying types of oils immediately from the surface.

Common drying types of oil include natural oils, sandalwood, cedarwood, etc. if you remove it much after, the lens can get damaged easily.

If you are using non-drying types of oil, we recommend that you wipe them off after the experiment. Such oils harden after a while, making it harder to clean off the surface.

Recommended Reading:


  1. Celestron
  2. Microscope World
  3. Cargille