Lab Exercise 2 (Microscopes)

Question 1

Define parfocal

Answer 1

Objectives of out microscopes are parfocal, which means they have been aligned in such a way that only slight adjustment in focus will be required when moving from one objective lens to the next.

Question 2

Define depth of field

Answer 2

the top to bottom area of a specimen that is in focus
a 2-d slice of field of view (as magnification ↑, DOV ↓)

Question 3

Define working distance

Answer 3

the distance between the objective lens and the slide/specimen

Question 4

Define magnification

Answer 4

apparent increase in the size of the specimen (makes object appear larger)

Question 5

Define resolution

Answer 5

the ability to distinguish two objects very close together (as separate from one another)
Affected by: quality of the lenses & amount of light

Question 6

Define micrometer calibration

Answer 6

how far apart (in microns) are the lines of the ocular micrometer? stage/ocular = um/lines

Question 7

Define ocular micrometer

Answer 7

ruler etched onto the ocular lens. Units are arbitrary b/c the lines don’t mean anything since measurement of species change as magnification changes

Question 8

Define stage micrometer

Answer 8

glass microscope slide with a rule etched onto the surface. Units are in microns (um). Used to calibrate the ocular micrometer (measure the distance between the lines of the ocular micrometer for each objective)

Question 9

Identify and explain the purpose of ocular lens

Answer 9

Provides 2nd magnification (ocular lens- 10X)
Virtual image of specimen

Question 10

Identify and explain the purpose of objective lens: scanning, low power, high dry, oil immersion (know magnifications)

Answer 10

Scanning (4X)-magnifies the least (birds eye view) 40 times larger
Low Power (10X) 100 times larger
High Dry (40X)- NO Oil 400 times larger
Oil Immersion (100X)- 1000 times larger
TOTAL MAGNIFICATION (ocular X objective)

Question 11

Identify and explain the purpose of revolving nosepiece

Answer 11

turns to allow different objective to be used

Question 12

Identify and explain the purpose of coarse and fine adjustment

Answer 12

Coarse focus adjustment knob (bigger knob)- Moves stage up and down in large amounts (to find DOF)
Fine focus adjustment knob (smaller knob)- moves objective lenses up and down in small amounts (to focus)

Question 13

Identify and explain the purpose of light source

Answer 13

Shines light on the specimen and lenses

Question 14

Identify and explain the purpose of substage condenser knob

Answer 14

Focus light on the specimen (cone like structure)

Question 15

Identify and explain the purpose of iris diaphragm lever

Answer 15

Slides right or left to control the iris diaphragm (and therefore amount of light on specimen)

Question 16

Identify and explain the purpose of mechanical stage & stage clips

Answer 16

moveable part of the stage with clips to hold onto the slide

Question 17

Identify and explain the purpose of mechanical stage control knob

Answer 17

moves mechanical stage (the slide) forward and back & left and right

Question 18

Identify and explain the purpose of ocular micrometer

Answer 18

ruler etched onto the ocular lens (used to measure the distance between the lines to calibrate)

Question 19

How do you calculate total magnification

Answer 19

Ocular lens (always 10) X Objective lens (4X, 10X, 40X, 100X)

Question 20

Understand the basic workings of the microscope (i.e.: when you move the object to the right, what direction does it appear to move toward?)

Question 21

Understand how to use a stage micrometer to calibrate an ocular micrometer
Explain why this must be done for every objective. To answer this question, think about what changes when you switch objectives and what does NOT change

Answer 21

We need to do stage/ocular which gets us microns per line (um/line) do that for every objective

Question 22

Define Contrast

Answer 22

the difference in the light absorption between the specimen and the background