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Simple Scope

Simple Scope. In a simple microscope the light passes through only a single lens. Advantage: Less optical distortion, simpler to build. Disadvantage: Less magnification. Compound Scope. Compound Scope: More than one lens Advantage = Potential for greater magnification.

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Simple Scope

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  1. Simple Scope In a simple microscope the light passes through only a single lens. Advantage: Less optical distortion, simpler to build. Disadvantage: Less magnification.

  2. Compound Scope Compound Scope: More than one lens Advantage = Potential for greater magnification

  3. Bright background, most common, what you will be using in lab. Additional Scope Classifications For viewing unstained cells.You will use this as part of demonstrations. We will also consider electron microscopy:High magnification, resolution, and contrast.

  4. Anatomy of a Microscope

  5. Electron microscopy • Magnetic coils replace the lenses. • A beam of electrons, instead of light is directed through the specimen. • X-rays have shorter wavelength, so magnification and resolution are much higher. • Samples usually stained or coated with metal ions to create contrast.

  6. What is Resolution? • The object of microscopy is not just to increase magnification, but to do so while retaining sufficient resolution. • Resolution is the ability to see two items as two separate things, i.e., two dots as two separate dots. • The resolution a microscope is capable of achieving is the smallest distance between two dots such that the two dots may be observed (resolved) as separate entities. • In less technical terms, lower resolution means an increased degree of fuzziness, i.e., less focusable specimens. • Greater resolution can be achieved by using oil immersion, by filtering out not-blue light, and by replacing light with electrons.

  7. Oil Immersion Increases Resolution Air has a different Index of Refraction from water (so light bends). Air has a different Index of Refraction from glass (so light bends). The Mineral Oil has the same Index of Refraction as glass (so light does not bend).

  8. Anatomy of a Microscope “High and Dry,” generally = 40x, must not touch oil. Only the “Oil Immersion” Objective (generally 100x) is to come in contact with Immersion Oil!

  9. Blue Light Increases Resolution Blue light has shorter wavelengththan other visible regions of the electromagnetic spectrum. Shorter wavelength results in higher resolution. Blue filter is inserted between light source and condenser.

  10. Contrast is Really Important • Contrast results from differences in the index of refractive between specimen and background, or within specimen = # visible shades in specimen. • Black vs. White = high contrast! • Unfortunately, unstained bacteria under bright-field microscopy are nearly transparent. • If you can’t contrast what you are looking at from the background then you can’t distinguish what you are looking at from the background. • Closing Iris Diaphragm increases contrast. • Contrast can also be increased by employing optical “tricks” such as with phase contrast. • “Stains provide contrast between bacteria and surrounding media.” • Types of staining:Simple staining, Differential staining, Special stains: capsule, endospore.

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