A lens bends light to make the image of an object appear smaller, larger, closer or farther away. Convex lenses concentrate light rays and are used as a magnifying lens. Concave lenses spread light rays.
A microscope uses light and lenses to produce an enlarged image of an object. Simple microscopes have only one lens. Compound microscopes have two or more lenses.
Parts of a Light Microscope
- Ocular - the magnifying lens closest to your eye.
- Body Tube - holds the lenses the proper distance apart.
- Revolving Nose Piece - holds the objective lens and allows objectives to be rotated for differing magnifications.
- Objectives are the lenses closest to the object (specimen).
- Scan objective is lowest power and shortest. Used to locate portion of specimen to observe.
- Low power objective - the middle length lens.
- High power objective - the longest length lens.
- Stage - supports the object (specimen).
- Stage Clips hold the object slides in place.
- Mirror - reflects light upwards through the slide.
- Substage Illuminator - shines light upwards through the slide.
- Base - supports the microscope.
- Diaphragm - controls the amount of light striking the slide.
- Arm - supports the body tube.
- Coarse adjustment knob - used to focus with scan objective.
- Fine adjustment knob - used to focus on low or high power objective.
- Inclination Joint - rotating joint so ocular can be positioned comfortably.
Procedure for using a Microscope
- Carry microscope with two hands, one on the arm the other on the base.
- With the arm towards you, place the microscope about 4" from the edge of desk/lab bench. Make sure power cords will not catch on the user or passersby.
- Verify the scan lens is in place and that the stage is a greatest distance from the scan lens.
- Look into ocular eyepiece; clean the lenses, mirrors or condenser if needed with lens paper.
- Place slide over hole in stage and secure with stage clips.
- Looking from the side, use the coarse adjust knob to bring the stage closest to the scan lens.
- Looking into the ocular, slowly increase the distance between the slide and the scan lens until the specimen is in focus.
- Locate area of specimen you wish to view.
- Slowly rotate nose piece until the low power lens clicks into place.
- On low and high power objectives, always use the fine adjustment knob, never use the coarse adjustment knob.
- Observe and sketch the specimen. To reduce eye strain, keep both eyes open.
- Never allow the objective lenses to contact a slide or specimen. If you must use the coarse adjust start again at step 6.
- When finished, rotate the scan objective into place.
- Use the coarse adjustment knob to drop the stage and remove the slide.
- Bring the body tube to an upright position and wrap the cord around the base.
- Return the microscope.