How to use an optical microscope
1. When using a monocular microscope, it is necessary to develop the habit of observing with the left eye (because the right hand is generally used to draw pictures). When observing, open both eyes at the same time, do not open one and close the other, because it is easy to fatigue. In order to train students to get used to observing with both eyes open at the same time, you can cut a rectangular piece of hard paper about 14cm long and 6cm wide, and dig a round hole near the left end with a diameter slightly smaller than the outer diameter of the upper end of the lens barrel. Put it on the upper part of the lens barrel, open both eyes at the same time when observing, use the right end of the paper to block the sight of the right eye, so that after a period of training, you can get used to opening both eyes at the same time, and then remove the paper.
2. The connection between the mirror arm and the mirror base of the straight microscope is a mechanical joint, which can be used to adjust the inclination of the mirror barrel for easy observation. The mirror arm should not be too backward tilted, generally no more than 40°. However, it is forbidden to use tilt joints when using temporary mounting slides for observation (when the lens barrel is tilted, the stage is also tilted, and the liquid on the slide glass is easy to flow out), especially when the slides contain acidic reagents, it is strictly forbidden to use them to avoid Defile the mirror body.
3. Use of eyepieces and objectives
Generally, an eyepiece with a moderate magnification (10×) and an objective lens with the lowest magnification are used to start observation, and gradually use an objective lens with a higher magnification to find a magnification that meets the experimental requirements.
When changing the objective lens, first observe with a low power lens and adjust to the correct working distance (the image is the clearest). If you use a high-magnification objective lens for further observation, you should move the part of the object image that needs to be magnified to the center of the field of view before switching to a high-power objective lens. Low magnification objective lens and high magnification objective lens are basically parfocal (same as high magnification focus).
It is generally accepted that the upper limit of effective magnification with any objective lens is 1,000 times its numerical aperture and the lower limit is 250 times its numerical aperture. For example, if the numerical aperture of the 40× objective lens is 0.65, the upper and lower limits are: 1000×0.65=650 times and 250×0.65≈163 times, respectively. The upper limit of the effective magnification is called invalid magnification, which cannot improve the observation effect. If the magnification is lower than the lower limit, the human eye cannot distinguish it, which is not conducive to observation. Generally the most practical magnification range is a number between 500 and 700 times the numerical aperture.
4. Use of oil immersion objectives
When using oil immersion objectives, generally do not use the same height focus. The same high-focus focusing is only applicable to the original objective lens of each microscope. It is a very favorable and convenient condition when using low-power and high-power objective lenses, but it is subject to certain restrictions when using oil-immersion objective lenses. When observing specimens (slides) without a cover glass, it is safer to use the same high focus adjustment, but for specimens with a cover glass, be careful to use it, because the working distance of the oil immersion objective lens is very small. Short, the height considered in the design and assembly is for standard thickness coverslips.
When using an oil immersion objective, only drip cedar oil on the slide. After the observation, it is necessary to clean it in time. If it is not done in time, the cedar oil will stick to dust, and the dust particles may wear the lens when wiping. The cedar oil will thicken and dry after being exposed to the air for a long time, making it difficult to wipe. Bad for the instrument. Wipe carefully and lightly. Wipe the front end of the oil immersion objective lens once or twice with a dry lens tissue to remove most of the oil, then wipe it twice with a lens tissue wetted with xylene drops, and finally wipe it once with a dry lens tissue. The cedar oil on the specimen can be removed by the "paper pulling method" (that is, cover a small piece of lens cleaning paper on the cedar oil, then drop some xylene on the paper, and pull the paper out while it is wet. clean, and generally does not damage unsmeared specimens with coverslips) wipe clean. The lens cleaning paper should also be dustproof. Generally, before use, each page is cut into 8 small pieces and stored in a clean small petri dish, which is economical and convenient to use.
5. How to use the concentrator
①. Reasons for using concentrators
When the magnification increases, on the one hand, the higher the magnification, the more the number of lenses, and the more light absorbed by the lens; It is inversely proportional to the square of the magnification, that is, the higher the magnification, the darker the field of view. In order to obtain sufficient brightness, a condenser must be installed to concentrate the light on the specimen to be observed.
②. The height at which the condenser should be located during observation
When observing, to ensure the best observation effect, the focusing focus of the condenser should just fall on the specimen. To achieve this condition, the height of the concentrator must be adjusted. When parallel light is used for illumination, the focal point of the condenser is about 1.25mm above the center of its upper lens plane. The height of the stage plane so that the focal point of light may fall on specimens placed on standard thickness slides. When using a glass slide that is thinner than the standard thickness to hold the specimen, the position of the condenser should be lowered accordingly, and when using a glass slide that is too thick, the focus of the light can only fall below the specimen, which is not conducive to fine observation.
③. Coordination between condenser and objective lens
The so-called cooperation here is to make the numerical apertures of the condenser and the objective lens consistent, so as to perform finer observation better. If the numerical aperture of the condenser is lower than that of the objective lens, part of the numerical aperture of the objective lens is wasted, thus failing to reach its highest resolution. If the numerical aperture of the condenser is larger than the numerical aperture of the objective lens, on the one hand, the specified resolution of the objective lens cannot be improved, and on the other hand, the clarity of the object image will be reduced due to the too wide illumination beam. The operation method of the cooperation between the condenser and the objective lens is: after completing the illumination and focusing operations, take off the eyepiece and look directly into the lens barrel, close the iris diaphragm under the condenser to the minimum, and then slowly open it up. Open until its diameter is exactly the same as the diameter of the field of view*, and then press the eyepiece to observe. Every time the objective lens is converted, such cooperation operations must be carried out in sequence. The frame of the iris diaphragm of some condensers is engraved with a scale indicating the opening aperture, which can be matched according to the scale.
