Light Microscopes David Fan I.
Light Microscopes A. Visible Light is Source of Illumination (up to 2000 X) 1. Bright Field Microscope a. Most widely used b. Light is transmitted through specimen c. Image is darker than bright surroundings (contrast) d. Can be used with live, unstained and preserved stain specimens 2. Dark Field Microscope a. Stop on condenser lenses blocks all light from entering objectives except peripheral light b. Same image on a darker field c. Good for living cells that can’t be stained or be exposed to heat d. Low detail, low visibility.
Dark field illumination, sample contrast comes from light scattered by the sample.
Cross-polarized light Bright field illumination, sample illumination, sample contrast comes from contrast comes from rotation of polarized absorbance of light in light through the the sample. sample.
Phase contrast illumination, sample contrast comes from interference of different path lengths of light through the sample.
3. Phase Contrast Microscope a. Transforms phase differences in light i. Light refracts differently when it hits various parts of the tissue b. Contrasted against a grey background c. Excellent resolution d. Contrast comes from interference of light 4. Differential- Interference Microscope a. Separates light into two parts combined to one plane b. Two prisms refract color, and add a 3D effect c. Unbelievable detail and color; only suitable for thin samples, not for thick samples B. Ultraviolet Rays are source of Illumination (Up to 2000 X) 1. Fluorescence Microscope a. Uses a UV radiation source and a protection filter b. Used with dyes that show fluorescence under UV rays c. Used in diagnosing infections caused by specific bacteria, protozoans, and viruses using fluorescent antibodies d. Forms a colored image against a black field 2. Confocal Microscope a. Light is focused on one point instead of all around b. Used on fluorescently stained specimens c. Allows for higher magnification