|  | Public Health Safety | Medical Research

Microscope Objectives Tutorial

Most microscopes contain at least three objective lenses that can be used to magnify the specimen being examined. In many cases, there will be a scanning lens to initially focus the specimen. A low-power objective lens and a high-power objective lens provide greater degrees of magnification. Some microscopes will also contain an oil immersion lens. The objective lenses are located on the nose-piece of the microscope and can be rotated into place.

  1. Scanning Objective Lens

    • A good microscopist will spend significant time using the scanning objective lens. Although this lens provides a low magnification, it allows for adjustments to be made that can improve the image under higher magnifications. After preparing the specimen on a slide and securing it to the stage, the scanning objective lens should be used to center the specimen in the field of view. It is important to take the time to focus the specimen correctly using the coarse adjustment knob followed by the fine adjustment knob. Adjust the light source so there is enough light to clearly see the specimen while still providing depth.

    Low and High Power Objective Lenses

    • After initial adjustments have been made using the scanning objective lens, the low power objective lens can be put into place. From this point forward, only the fine adjustment knob should be needed to focus the specimen. After the image is sharply focused, the stage can be adjusted to center the image. The light source may also be adjusted slightly to provide the best depth.

      If the high power magnification is desired, this lens can be put into place after adjustments have been made with the low power objective lens. The same sequence of steps used for the low power objective lens should be taken with the high power objective lens. At this point, if the fine adjustment knob does not clearly focus the image, it is important to move back down to the scanning objective lens and start over. Using the coarse adjustment knob with the high power objective lens can cause a slide to break because the lens is close to the slide.

    Oil Immersion Lenses

    • Oil immersion lens typically provide a magnification of 100x. If using an oil immersion lens, be sure that immersion oil is available. After making adjustments with the high power objective lens, rotate the nose-piece so that all lenses are out of the way of the slide. Place a small drop of immersion oil on the slide and rotate the oil immersion lens into place. Use only the fine adjustment knob to sharply focus the image and adjust the stage to center the specimen.

      After finishing with the oil immersion lens, use the nose-piece to rotate the lens away from the slide; use lens paper to remove any oil that may be on the lens.

Medical Research - Related Articles