precaution while using microscope

Always focuswith thescanning power objectivelens first. Focus away from the specimen with thecoarse adjustment knobwhile viewing the object on scanning or low power. While using the high power objective, thefine adjustment knobshould be utilized for focusing because theworking distancedecreases as magnification increases.To increase magnification, always center an object of interest using themechanical stage knobsbefore rotating thenosepiece. Adjust thelight intensityusing theiris diaphragmattached to thecondensor. Do not drag the microscope across the lab table. Clean all lenses withlens paperbefore and after use of a microscope. Protect the microscope as you return it to its cabinet by replacing theplastic coverand carrying it with two hands (one holding it by thearmthe other supporting it by thebase).

When you instructor gives you the go ahead, you may acquire a microscope from the cabinet in the front of the classroom. Carrying a microscope is a two handed job. Grasp the arm of the scope with one hand (the built in handle on CH 30 scopes) and as you remove the scope from the shelf place your other hand under the base. NEVER carry the scope with one hand or swing it about. These are delicate, expensive tools and must never experience rough handling or be dropped! Notice how the electrical cord is wrapped around the neck of the microscope. The cord should be tightly wrapped. In addition, the nosepiece should be adjusted to place the 4X lens in the locked position and the stage should be lowered. Move the nosepiece if this is not the case. Raise the stage and unwrap the cord. Turn the rheostat to 1, the lowest power level, plug the microscope in and flip the toggle to on. We always begin with the rheostat turned low in increase the working life of the bulb.

Begin with the stage in the lowered position. Rotate the nosepiece of the microscope until the 4X objective is in the locked position.. Place the slide into the holder and use the coarse focus to raise the stage to the highest position. NOTE. do NOT raise the stage using the coarse focus if the 40X or 100X objective is in place. Adjust the rheostat to an intermediate position so that the light is not glaringly bright nor dim. Look through the ocular lenses and lower the stage using the coarse focus until the sample comes into focus. With a sample in place you can now adjust your ocular lenses. See the end of this page for deatail on using the oil immersion lens.

The intra ocular distance is adjusted simply by pulling the eyepieces apart or pushing them together. When you have the intra ocular distance set correctly, you should see a single image of your sample. You should note the width of your setting on the scale behind the right ocular so you can reset the lenses to your distance after someone else has used the microscope.

You need to store the microscope in the correct fashion. Turn the rheostat to 1and then toggle the light off. Turn the nosepiece to the 4X objective and raise the stage to a high position. Wrap the electrical cord snugly around the arm and then lower the stage to help hold the cord in place. Using both hands to carry the scope, return it to the numbered slot in the microscope cabinet.

To examine bacteria and other very small objects, we will need to use the oil immersion (100X lens). Special techniques must be used when using the 100X objective. With the 10 fold increase in magnification provided by the ocular lens, we are approaching the theoretical limit of light microscopy so must obtain the best possible resolution in order to get a clear image the sample. Because light travels more slowly through glass and most other media than it does through air, light leaving air and passing though glass is bent. You have probably observed this bending phenomenon when looking at objects in water whose position and appearance seem distorted. To prevent this distortion from occurring between the sample and the objective lens, we fill the space between with immersion oil which has the same optical properties as glass. Without immersion oil, objects seen under the 100X lens will appear fuzzy even at the best possible focus.