Chapter 3: The Microscope

working distance

- measured in mm; distance from bottom of the objective lens to surface of the slide

True or False? You should always begin observation of specimens with the oil immersion lens

FALSE - w/ objective lens

field

area you see through microscope

40x

high power

mechanical stage

holds the slide in position for viewing and has two adjustable knobs that control the precise movement of the slide

The microscope slide rests on the ______________ while being viewed.

stage

100x

oil immersion

depth of field

thickness of the plane that is clearly in focus; is greater at lower magnification

coarse adjustment knob

this knob allows you to make large adjustments to the height of the stage to initially focus your specimen

fine adjustment knob

this knob is used for precise focusing once the initial coarse focusing has been completed

10x

low power

resolution

- resolving power - ability to discriminate two close objects as separate - determined by the amount and physical properties of the visible light that enters the microscope - the more light delivered to the objective lens, the greater the resolution - size of objective lens opening decreases with increasing magnification, allowing less light to enter the objective (must increase light intensity at higher magnifications)

Rules for compound microscope

- when transporting microscope, hold it in an upright position, with one hand on its arm and the other supporting its base - use only special grit-free lens paper to clean the lenses --- circular motion to wipe the lenses, clean all lenses before and after use - always begin focusing process w/ lowest-power objective lens in position, changing to the higher-power lenses as necessary - use the coarse adjustment knob only w/ the lower-power objective lens - always use a coverslip with wet mount preparations - before putting microscope away, remove slide form stage, route the lowest-power objective lens into position, wrap the cord nearly around the base, replace dust cover or return microscope to the appropriate storage area - never remove any pars from the microscope; inform your instructor of any mechanical problems that arise

If the ocular lens magnifies a specimen 10x, and the objective lens used magnifies the specimen 35x, what is the total magnification being used to observe the specimen? _____________

10x x 35x = 350x

Your lab microscope is "parfocal." What does this mean? A - the specimen is clearly is focus at this depth. B - the slide should be almost in focus when changing to higher magnifications C - you can easily discriminate two close objects as separate

B - slide should be almost in focus when changing to higher magnifications

How do you clean the lenses of your microscope? A - with a paper towel B - with soap and water C - with special lens paper and cleaner

C - with special lens paper and cleaner

head

attaches to the nosepiece to support the objective lens system - also provides for attachment of the eyepieces which house the ocular lenses

ocular lens(es)

binocular microscopes will have 2 lenses located in the eyepieces at the superior end of the head - most ocular lenses have a magnification power of 10x - some microscopes will have a pointer and/or reticle (micrometer), which can be positioned by rotating the ocular lens

base

bottom of the microscope - provides a sturdy flat surface to support and steady the microscope

total magnification (TM)

equal to the power of the ocular lens multiplied by the power of the objective lens used ex: if ocular lens magnifies 10x and objective lens being used magnifies 45x, the total magnification is 450x

iris diaphragm lever

iris diaphragm is a shutter within the condenser that can be controlled by a lever to adjust the amount of light passing through the condenser - lever can be moved to close the diaphragm and improve contrast. if your field of view is too dark, you can open the diaphragm to let in more light

substage light

located in the base - the light from the lamp passes directly upward through the microscope

light control knob

located on the base or arm - this dial allows you to adjust the intensity of the light passing through the specimen

real image

objective lens magnifies the specimen to produce this, which is projected to the ocular

what are the two lenses involved in magnification in a microscope

ocular lens and objective lens

stage

platform that the slide rests on while being viewed - stage has a hole in it to allow light to pass through the stage and through the specimen

Compound microscope

precision instrument and should always be handled with care

virtual image

real image is magnified by ocular lens to produce this, which is what your eye sees

nosepiece

rotating mechanism connected to head - generally, it carries 3 or 4 objective lenses and permits positioning of these lenses over the hole in the stage

4x

scanning

parfocal

slide should be in focus at the higher magnifications once you have properly focused at the lower magnification

condenser

small non magnifying lens located beneath the stage that concentrates the light on the specimen - condenser may have a knob that raises and lowers the condenser to vary the light delivery - generally, the best position is close to the interior surface of the stage

objective lenses

these lenses are attached to the nosepiece - usually, a compound microscope has four objective lenses: scanning (4x), low-power (10x), high-power (40x), and oil immersion (100x) lenses - typical magnifying powers for the objectives are listed in parentheses

arm

vertical position of the microscope that connects the base and head