Microscope and its functions | Cheat Sheet Biology

The microscope is one of the microbiologist's greatest tools. It allows for the

visualization of small particles, including microbes, whichindividuallyare too small

to be seen with the human eye. With the help of proper illumination, a microscope

can magnify a specimen and optically resolve fine detail. This introduction to

microscopy will include an explanation of features and adjustments of a

compoundbrightfieldlight microscope,which magnifies images using a two lens

system.

Before reading the following discussion of the theory of the microscope, please

familiarize yourself with the names of the microscope parts shown in Figure 2 and

their function.

1.Eyepiece/Ocular lens:Lens in which the final magnification occurs. Often is

at10X magnification, but can be different.

2.Revolving nose piece: Holds multiple objective lenses in place. The base of the

nose piece can rotate, allowing each of the lens to be rotated into alignment with

the ocular lens.

3.Objective lenses: Initial magnification of your specimenoccurs here.Most

brightfield light microscopeshave3 objective lenses seated into the resolving nose

piece base.

4.Coarse focusing knob: larger of the two knobs, the coarse adjustment knob

moves thestageup or down to bring the specimen into focus. It is very sensitive,

even small partial rotation of this knob can bring about a big change in the vertical

movement of the stage. ONLY use coarse focusing at the beginning with the 4X,

10Xlow poweredobjectives in place. If you use it with the higher powered

objectives, it can damage the objective ifyou crash the lens through your glass

specimen slide.

5.Finefocusing knob:smaller of the two knobs, the fine adjustment knobbrings

the specimen into sharp focus under low power and is used for all focusing when

using high power lenses such as the 100x oil immersion lens.

6/9.Stage & Mechanical stage:The horizontal surface where you place the

slidespecimenis called the stage. The slide is held in place by spring loaded clips

and moved around the stage by turning the geared knobs on

themechanicalstage. The mechanical stage has two perpendicular scales that

can be used to record the position of an object on a slide, usefulto quickly relocate

an object.

7.Illuminator: contains the light source, a lamp made either of an incandescent

tungsten-halogen bulb or an LED. There is normally a switch to turn on/off or

arheostatlocated on the side that you can use to adjust the brightness of

thelight.

8.Diaphragm and Condenser: the diaphragmcontrols the amount of light

passing from the illuminator through the bottom of the slide, there is a small lever

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The microscope is one of the microbiologist's greatest tools. It allows for the visualization of small particles, including microbes, which individually are too small to be seen with the human eye. With the help of proper illumination, a microscope can magnify a specimen and optically resolve fine detail. This introduction to microscopy will include an explanation of features and adjustments of a compound brightfield light microscope, which magnifies images using a two lens system. Before reading the following discussion of the theory of the microscope, please familiarize yourself with the names of the microscope parts shown in Figure 2 and their function.

Eyepiece/Ocular lens: Lens in which the final magnification occurs. Often is at 10X magnification, but can be different.
Revolving nose piece : Holds multiple objective lenses in place. The base of the nose piece can rotate, allowing each of the lens to be rotated into alignment with the ocular lens.
Objective lenses : Initial magnification of your specimen occurs here. Most brightfield light microscopes have 3 objective lenses seated into the resolving nose piece base.
Coarse focusing knob : larger of the two knobs, the coarse adjustment knob moves the stage up or down to bring the specimen into focus. It is very sensitive, even small partial rotation of this knob can bring about a big change in the vertical movement of the stage. ONLY use coarse focusing at the beginning with the 4X, 10X low powered objectives in place. If you use it with the higher powered objectives, it can damage the objective if you crash the lens through your glass specimen slide.
Fine focusing knob: smaller of the two knobs, the fine adjustment knob brings the specimen into sharp focus under low power and is used for all focusing when using high power lenses such as the 100x oil immersion lens. 6/9. Stage & Mechanical stage : The horizontal surface where you place the slide specimen is called the stage. The slide is held in place by spring loaded clips and moved around the stage by turning the geared knobs on the mechanical stage. The mechanical stage has two perpendicular scales that can be used to record the position of an object on a slide, useful to quickly relocate an object.
Illuminator : contains the light source, a lamp made either of an incandescent tungsten-halogen bulb or an LED. There is normally a switch to turn on/off or a rheostat located on the side that you can use to adjust the brightness of the light.
Diaphragm and Condenser : the diaphragm controls the amount of light passing from the illuminator through the bottom of the slide, there is a small lever

used to achieve the optimal lighting. The condenser is a lens system that focuses the light coming up from the illuminator onto objects on the slide. The Optical System. The optical system of a compound microscope consists of two lens systems: one found in the objective(s) lens(es) (Fig. 2, part 3); the other in the ocular (eyepiece) (Fig. 2 part 1). The objective lens system is found attached to a rotating nosepiece (Fig. 2, part 2). A microscope usually has three or four objectives that differ in their magnification and resolving power. Magnification is the apparent increase in size of an object. Resolving power is the term used to indicate the ability to distinguish two objects as separate. The most familiar example of resolving power is that of car headlights at night: at a long distance away, the headlights appear as one light; as the car approaches, the light becomes oblong, then barbell-shaped, and finally it becomes resolved into two separate lights. Both resolution and magnification are necessary in microscopy in order to give an apparently larger, finely detailed object to view. Look at the engravings on the objective lenses and note both the magnification (for example: 10X, 40X, 100X) and the resolution given as N.A. = numerical aperture, from which the limit of resolution can be calculated:

through the oil. Without the oil, light passing through the glass microscope slide and specimen would be refracted (bent) when it entered the air between the slide and the objective lens. This refracted light might still be able to contribute to the image of the specimen if the objective lens is large. However, at the higher magnification, the objective lens is small, so is unable to capture this light. The loss of this light leads to loss of image detail. Therefore, at higher magnifications, the area between the slide and the lens is modified to have the same (or nearly the same) refracting qualities (refractive index) as the glass and specimen by the addition of immersion oil. Watch this NC BioNetwork video (https://youtu.be/-0EvnroWpVc) on oil immersion. For more information, read this article (https://www.microscopeworld.com/t-us...rsion_oil.aspx). To use an oil immersion lens, place a drop of oil on top of the dried specimen on the slide and carefully focus the microscope so that the objective lens is immersed in the oil. Any lens, which requires oil, is marked "oil" or "oil immersion." Conversely, any lens not marked "oil" should NOT be used with oil and is generally not sealed against oil seeping into and ruining the objective. https://bio.libretexts.org/Courses/North_Carolina_State_University/ MB352_General_Microbiology_Laboratory_2021_(Lee)/03%3A_Microscopy/ 3.01%3A_Introduction_to_the_Microscope Non-optical parts Base The base is also known as the foot which is either U or horseshoe-shaped. It is a metallic structure that supports the entire microscope. Pillar The connection between the base and the arm are possible through the pillar. Arm The arm is also known as the limb which is a metallic handle forming the connection between the arm to the inclined joint. The stage and the body tube is supported by the arm. Inclination Joint If the observation has to be done in a sitting position, then the microscope can be tilted using the inclination joint.

Stage It is the metallic platform that is fitted to the lower part of the arm with a hole in the center. The microscopic slides are placed on the stage either by using side clips or by mechanical stage clips. Body Tube The main purpose of the body tube is to hold the objective and ocular lenses at the two ends. The end where the ocular lens is present is known as the head while the end where the objective lens is placed is known as the nose piece. For the passage of light rays through the body tube, there is a pathway. Draw Tube The upper end of the body tube has a small fixed tube which is known as the drawtube. The main function of the drawtube is to hold the ocular lens. Rack and Pinion To bring the object under focus, the rack and pinion are either attached to the body tube or the stage. Adjustment Screws These are two pairs of adjusting screws that are used either for a coarse adjustment or for fine adjustment. When a fine adjustment is made, the body tube or the stage moves extremely short distances while in coarse adjustment, the body tube and stage move up. Through fine adjustment, a sharp image can be obtained. Automatic Stop The rack and pinion have a small screw that is used for stopping the downward sliding of the body tube. This prevents damage to the objective lens. Optical Parts Diaphragm The amount of light falling on the object can be controlled through the diaphragm. It is present below the stage. The disc and iris are the two types of diaphragm.

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