# Microscope 🔬 --- **Microscopes** are a tool we use in the [[labs]] that allow us to see things that are too small to see with the naked eye, like individual [[cell|cells]]. - [[light microscope|Light microscopes]] are what we traditionally think of as microscopes. They have lenses that **bend light** in order to magnify the subject. - [[electron microscope|Electron microscopes]] are much more technical, and operate at a much higher resolution. They use beams of [[atom#Electrons Electron Shells|electrons]] or [[radiation]] to magnify the subject. ## Terms **Working distance** is the distance between the specimen and the objective lens. The microscopist does not want to touch the specimen with her/his lens and risk damage to the lens. **Depth of field** refers to the distance between the closest and farthest objects that are in focus. A **parfocal lens** is a lens that stays in focus then the magnification/focal length is changed. Or when one objective lens is in focus, then the other objectives will also be in focus. ## Resolution **Resolution** describes the ability to distinguish two points, a certain distance apart, as separate points. The better the resolution, the "sharper" the image appears. The **limit of resolution** (or resolving power) is a measure of the ability of a lens to separate in the image adjacent details that are present in the object. In other words, it is the distance between two points in the object that are just resolved in the image. For example: The limit of resolution of your eye is approximately 0.1 mm. What does this mean? Your eyes can distinguish two objects that are 0.1 mm apart as two separate objects. If two points are only 0.05 mm apart, your eye would "see" them as a single point. This distance would be beyond the limit of resolution of your eyes. When describing resolution, use of the terms "greater" or "smaller" may be misleading. The smaller the limit of resolution, the better the resolution. Two main things determine the limit of resolution: - The **wavelength of light** passing through the specimen. The shorter the wavelength, the better the resolution. The light microscope's resolution is limited by the wavelengths of visible light. - Numerical **aperture** of the lens. The greater the numerical aperture (NA), the better the resolution. NA is usually indicated on the side of each lens. Microscope | Resolution -----------|----------------: [[light microscope#^dissecting\|Dissecting light]] | 120 nm (?) [[light microscope#^compound\|Compound light]] | 200 nm (?) [[electron microscope#^sem\|Scanning electron]] | 5-10nm [[electron microscope#^tem\|Transmission electron]] | 1.0 nm ## Magnification **Magnification** describes the degree to which the specimen is enlarged by a microscope. Magnification is accomplished by one or more lenses which refract (bend) the light. Microscope | Magnification -----------|----------------: [[light microscope#^dissecting\|Dissecting light]] | 30x [[light microscope#^compound\|Compound light]] | 40-1000x [[electron microscope#^sem\|Scanning electron]] | 200-500,000x [[electron microscope#^tem\|Transmission electron]] | 1,000,000x ___