Microscope parts
01 // How a compound microscope works
A compound light microscope magnifies a sample in two stages: light passes up through the specimen and through an objective lens close to the sample, which produces a magnified image. That image is magnified a second time by the eyepiece lens you look through — 'compound' refers to using two lenses in sequence rather than just one.
02 // The main parts
1. Eyepiece (ocular lens)
The lens you look through, usually magnifying 10x on its own.
2. Objective lenses
A rotating set of lenses (often 4x, 10x, and 40x) that magnify the specimen from just above it.
3. Stage and stage clips
The flat platform that holds the slide in place under the lenses.
4. Diaphragm
Controls how much light passes up through the specimen from below.
5. Coarse and fine focus knobs
Coarse focus makes large adjustments; fine focus makes small, precise ones once the image is close to sharp.
6. Arm and base
The arm is what you carry the microscope by; the base supports it and often houses the light source.
03 // Using it correctly
- Total magnification is the eyepiece power multiplied by the objective power — a 10x eyepiece with a 40x objective magnifies the specimen 400 times.
- Always start focusing on the lowest-power objective, then switch to higher power once the image is roughly in focus — jumping straight to high power on an unfocused slide can crash the lens into the slide.
- Carry a microscope with two hands: one under the base, one gripping the arm.
04 // Questions people ask
How do you calculate a microscope's total magnification?
Multiply the eyepiece lens power by the objective lens power currently in use. A common combination — a 10x eyepiece with a 40x objective — gives a total magnification of 400x.
Why do you start focusing on low power instead of high power?
The distance between the lens and the slide is much smaller at high power, so focusing on a completely unfocused slide at high power risks driving the lens directly into the slide. Starting on low power gets the image roughly focused at a safer distance first.
What does the diaphragm control on a microscope?
The diaphragm controls how much light passes up through the specimen from the light source below. Too much light can wash out a transparent specimen, while too little makes it hard to see any detail at all.