Microscopes Flashcards
1
Q
Objective lens
A
- short focal length/group of lenses
- biggest part of the magnification of the microscope
- some lenses remove optical defects of the frontal lens (distortion, chromatic aberration)
- forms true real magnified image
2
Q
Eyepiece lens
A
Ocular
- two spherical lenses
- forms large virtual image
- final image virtual, magnified and reversed
3
Q
Optical condenser
A
- collimate the light beam of the light source and to focus it onto the object
- contributes to quality of image
4
Q
Magnification
A
ratio of the linear dimensions of the image and of the object
- magnification of the optical microscope Wm is given by the product of the linear magnification of the objective Wobj and the angular magnification of the eyepiece Woc
Wm = Wobj x Woc
5
Q
Resolution
A
- ability to distinguish neighbouring objects
- smaller distance, able to distinguish, larger resolution
6
Q
Distance d, in the optical microscope
A
- is defined by the size and the position of the frontal lens of the objective
- by the refractive index n, of the medium between the frontal lens and the object
- and by the wavelength of the light illuminating the object
d = 0.61 x λ/n.sinα
α - half maximal angle between the incident beam and frontal lens of the objective = aperture angle
7
Q
Numerical aperture
A
A = n sin α
8
Q
Refractive index
A
dry object, vacuum, air, = 1
- if space between frontal lens of the objective and the investigated object is filled with a substance with n>1, d decreased and resolution increases
- substance used = immersion liquids, cedar oil n=1.52
- necessary when microscope has high magnification
9
Q
Dark field observation
A
- used when investigated object is small, transparent, and unstained
- when it strongly disperses the incident light
- light transmitted by object is minimised and only light dispersed by object falls on objective
- object seen bright
10
Q
Phase contrast observation
A
- used when object is unstained and contains structural elements with different n’s
- inserting suitable rings in condenser and objective, difference between n is transformed into an amplitude difference thus increasing contrast
11
Q
Observation with polarised light
A
- suitable for investigation of a transparent unstained object containing optically active structures
- object placed between polariser and analyser of the polarising microscope only the optically active structures are visible