Focusing Procedures
A compound light microscope is easy to use just as long as you take the time to familiarize yourself with its components and respective functions. After that, you can usually figure out the proper way of focusing your microscope on a sample or specimen but in case that you really want to be sure of what you’re doing, here are some tips about the focusing procedure of a compound light microscope.
Terms to Remember
Regardless of what kind of microscope you’re using, you’ll be hearing the following terms often and having a good grip on their meanings will make it easier for you to follow focusing procedures and instructions. Magnification – this refers to the capabilities of a microscope in magnifying the image of a sample or specimen. Resolving Power – this ensures that any magnified image will have proportional increase and improvement of the image’s details. Its technical definition is the least amount of distance between 2 objects and at which they can be distinguished separately; resolving power is also a function of the light wavelength and quality of optics utilized. Working Distance – this refers to the distance between the specimen or sample and the microscope’s objective lens; at high power magnification, working distance is considerably short and vice versa.
Microscope Parts You Adjust When Focusing on a Specimen
There are certain parts of a microscope you almost always use when focusing on a specimen. It’s best to remember what their functions are as well as their effects on the image. Know how they interact with other parts of the microscope, too.
Coarse Focus Knobs – These are the bigger pair of knobs found on the side of a microscope. They move the microscope’s body tube or stage up and down. Remember which direction you need to rotate the knob to lower the stage or body tube. Messing this up could damage your objective lenses or the specimen itself.
Fine Focus Knobs – These control the microscope’s focus on the sample or specimen. Adjusting them will have a very tiny effect on stage positioning as well. As your experience and ease in using microscopes grow, you’ll notice that you’re using these more and more than the coarse focus knobs.
Condenser – Many microscope users miss the importance of the condenser when focusing on a specimen. The condenser basically allows the user to control the amount of light you hitting your specimen.
Filter – Use this to reduce or increase light intensity.
Objectives – These are responsible for the clarity and detail of magnified images.
Eyepieces – These are responsible for magnifying the image of your sample or specimen. They commonly work hand in hand with objectives.
Steps on Focusing Your Microscope
Step 1 Always start adjusting the microscope at low power. This will make it easier for you to gauge what else you need to change in order to improve image resolution. Hold the nosepiece only to change objectives. Start with the lowest power objective you have. Once you hear a clicking sound then that means your objective lens is already in place. At this point, you just have to make sure that the specimen’s image is at the center of your microscope’s field of view.
Step 2 With that done, try observing your specimen from the sides. Use the coarse knobs of your microscope to adjust the stage positioning. Rotate it to the appropriate direction in order to elevate the stage. Make sure however that you don’t lift the stage so high the objective lens would come into contact with the glass slide or any part of the specimen. When you do that, you could damage both your specimen and objective lenses. You might say that damaging your specimen is nothing if it’s just a tiny pebble, but objective lenses are quite expensive to replace or even repair so do take care when moving your stage!
Step 3 Once you’re done with Step 2, move on to taking a peek at your microscope through the eyepiece – or eyepieces if it offers dual view. Now check your diaphragm and illuminator then adjust light levels until you obtain the maximum amount you’re comfortable with. Remember that while you want enough light to make the whole image clear, you don’t want the light to become too strong that it makes it hard to see the image.
Step 4 Finished? Then rotate the coarse focus knobs again but this time to lower the stage. Peek through the eyepiece while doing so. Stop lowering the stage once the entire image is visible. You can use the fine focus knobs as well to attain ideal focus. Move the slide if you wish and that’s it!
See http://www.compound-light-microscope.com for more information about this basic type of microscope.
