All About Oil Immersion Objective Lens

All About Oil Immersion Objective Lens

Oil lens is a kind of objective lens of microscope. The medium of microscope objective includes air, water and oil, and the water oil are used for high-resolution microscope objective.

The full name of oil lens is oil immersion objective. The difference between it and other objective lenses is that when in use, the space between the slide and the objective lens is not air, but filled with immersion oil, so as to improve the magnification efficiency of the microscope.

Generally speaking, the length of oil lens is longer than that of low and high power lens. The lower edge of the lens is generally engraved with a circle of black line or white line and engraved with 100X/1.25(oil).

When using the microscope oil objective, it is necessary to drop immersion oil on the glass slide.

The lens of the oil lens is very small. When the light passes through the air between the glass slide and the oil lens, refraction or total reflection occurs due to different medium density, so that the light entering the lens is reduced and the object image is not clear; If immersion oil (n=1.515) similar to the refractive index of the glass (n=1.52) is added between the oil lens and the glass slide, the light entering the lens will increase, the brightness of the visual field will be enhanced, and the object image will be bright and clear.

Remark:

1) After finding the specimen with a low-power objective lens, change to a high-power objective lens for observation, move the specimen to the center of the field of vision, place the diaphragm at the maximum.

(2) Remove the sample piece, drop 1 or 2 drops of immersion oil on the upper condenser, and then put the sample piece back to the original position, so that the underside of the slide is in close contact with cedar oil to prevent air saturation in the oil. However, in normal operation, this step can be omitted.

(3) Drop a 1 drop of immersion oil on the cover glass or on the part required to be observed by the smear specimen, transfer the oil lens to the optical axis, and carefully adjust the coarse focusing screw to make the lens descend slowly. Please be carefull, observe the distance between the front end of the oil lens and the specimen, and stop the descent when the front end of the oil lens starts to touch the oil drop. This operation process must be very careful to prevent the oil lens from crushing the specimen and damaging the oil lens.

(4) Observe from the eyepiece with the left eye and adjust the fine-tuning focus knob to slowly focus the lens to the correct working distance to see the object image of the specimen clearly. Please note: the coarse and fine-tuning focal knob should not be mistaken. The cover glass should be thin. If it is too thick, it cannot be focused, otherwise it is easy to crush the specimen and damage the lens.

(5) Adjust the iris diaphragm to match the numerical aperture of the condenser with the oil mirror to obtain a clear image.

(6) After the observation, the cleaning work shall be done in time. First raise the oil lens to 1.5cm away from the specimen, turn the oil lens away from the optical axis, gently absorb the oil on the oil lens with dry lens wiping paper, then wipe it twice with lens wiping paper soaked with alcohol with a concentration of more than 75 percent , and finally gently wipe it twice or three times with clean lens wiping paper. Wipe off the oil drops on the condenser in the same way. The cedar oil on the specimen can be wiped by pulling paper, that is, a small piece of mirror wiping paper is used to cover the oil droplets of the specimen, and then some alcohol with a concentration of more than 75 percent is dropped on the paper, and the paper is pulled out while it is wet. In this way, the smear specimen can be wiped clean without damaging it for 3 or 4 times.

Some people will choose to wipe the oil lens with xylene, but xylene is a solvent, which will decompose the glue used to bond the front lens of the objective lens. Long term use of xylene is easy to make the front lens of the objective lens fall off.