Proper microscope maintenance is essential to preserve delicate components and ensure high-resolution images, as dirty or scratched lenses will refract light in unintended ways. Routine care includes cleaning lenses with specialized lens paper, protecting the bulb from breakage, and covering the instrument when not in use. To avoid physical damage during operation, users must never push an objective into a slide, should not use the coarse focusing knob with $${}40	imes$$ or greater objective lenses, must only apply immersion oil with specialized objectives (typically $${}100	imes$$), and must meticulously clean immersion oil from all lenses immediately after use.

Microscope Maintenance and Care

At very high magnifications, the small amount of air between a specimen and the lens can scatter light rays before they are focused, compromising resolution due to the large difference in refractive indices between air and glass. To prevent this, a drop of immersion oil is applied to fill the space between the specimen and a specialized oil immersion lens. Because the oil has a refractive index very similar to that of glass, it increases the maximum angle at which light can enter the lens, thereby capturing more light and improving the resolution of the image.

Google

The brightfield microscope, considered the most commonly used type of microscope, is a compound microscope that employs two or more lenses to produce a dark image of a specimen against a bright background. These microscopes are illuminated by a light source focused by a condenser lens, and they can be monocular (possessing a single eyepiece) or binocular (possessing two eyepieces), with each eyepiece containing an ocular lens.

Brightfield Microscopes

Refraction is a behavior exhibited by light waves where they change direction as they enter a new medium. This occurs because different transparent materials transmit light at varying speeds, meaning light changes speed when passing from one material to another. The degree of refraction depends on the angle of the incoming light.

Refraction

Resolution is defined as the ability to tell that two separate points or objects are distinct from one another. In microscopy, a low-resolution image appears fuzzy, whereas a high-resolution image appears sharp. Resolution is primarily affected by two factors: the wavelength of the light or electron beam used (with shorter wavelengths yielding higher resolution) and the numerical aperture of the lens. Additionally, resolution can be increased by using stains that enhance the contrast of the specimen.

Resolution

https://openstax.org/details/books/microbiology/

Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

OpenStax Microbiology Textbook

Oil Immersion Lenses

The total magnification achieved by a compound microscope is determined by the product of the ocular lens magnification and the objective lens magnification. For instance, if an ocular lens magnifies by $${}10	imes$$ and the selected objective lens magnifies by $${}40	imes$$, the total magnification of the resulting image would be $${}400	imes$$.

Total Magnification

A compound light microscope consists of multiple interacting structural and optical components. The base houses an illuminator and a rheostat for lighting. An arm supports a stage equipped with x-y mechanical knobs to secure and position the specimen. Below the stage, a condenser and diaphragm regulate the incoming light. Above the stage, objective lenses on a revolving nosepiece and ocular lenses within the eyepieces provide magnification. Finally, coarse and fine focusing knobs on the arm adjust the stage's height to bring the specimen into sharp focus.

Parts of a Microscope

Brightfield microscopes can produce maximally sharp images at magnifications up to approximately $${}1000	imes$$. Increasing magnification beyond this point results in a larger image but does not provide any additional resolution. This specific magnification range allows observers to clearly see objects as small as bacteria, which become visible around $${}400	imes$$, but it is not powerful enough to visualize smaller structures like viruses.

Brightfield Microscope Magnification Limit

A darkfield microscope is a brightfield microscope modified with a small opaque light stop placed on the condenser. This component blocks most direct light from the illuminator, ensuring that the only light reaching the objective lens is light scattered, refracted, or reflected by structures in the specimen. Consequently, it creates high-contrast, high-resolution images showing bright objects on a dark background without the use of stains, making it exceptionally useful for viewing live, delicate specimens that might be killed by staining procedures.

Darkfield Microscopes

The cornea is the transparent outer layer of the eye that serves as a protective barrier between the inner eye and the external world. It also plays a crucial role in focusing the light waves that enter the eye.

Cornea

The refractive index of a material is a measure of the extent to which it slows the transmission speed of light relative to empty space. When light passes from one material to another, a large difference between their refractive indices results in a significant amount of refraction. For instance, water has a higher refractive index than air because light moves much more slowly through water, causing the light to change direction greatly when entering water from air.

Refractive Index

An optical lens is an object with a curved boundary, functioning similarly to a collection of prisms, that collects striking light and refracts it so that it all meets at a single focus or image point. Lenses operate on the principle of refraction; when light crosses into the lens material (which typically has a higher refractive index than its surroundings), its direction turns closer to perpendicular to the boundary, bending more toward a normal.

Optical Lenses

Dispersion is the separation of white light into its component colors, creating a rainbow-like spectrum. This phenomenon occurs when light passes through a material like a prism, because the material's refractive index differs for different frequencies of light, causing each color to be refracted in a different direction.

Dispersion

An opaque light stop is a small, opaque disk (approximately 1 cm in diameter) placed between the illuminator and the condenser lens of a darkfield microscope. Its primary function is to block most of the direct light traveling from the illuminator, which produces a hollow cone of light focused directly onto the specimen. This critical modification ensures that only light refracted or reflected by the specimen itself can enter the objective lens.

Opaque Light Stop

Numerical aperture is a measure of a lens's ability to gather light. It is a critical factor that affects the resolution of an image; the higher the numerical aperture, the better the resolution produced by the microscope.

Numerical Aperture

Shorter wavelengths are able to resolve smaller objects. For example, an electron microscope has a much higher resolution than a light microscope because it uses an electron beam with a very short wavelength, as opposed to the long-wavelength visible light used by a light microscope.

Learn Before

Related

Learn After