Lecture 1 - Light microscope Flashcards
Why can we see things?
Photoreceptor cells in retina activated by photons of light with certain wavelengths
Lens focuses light emitted or bounced off an object
Why are some things not visible
Not enough photons
Wrong kind of photons (outside of visible spectrum
Objects too small of photoreceptors to resolve
Objects dont interact with or emit visible light
Objects interact with light the same as surrounding medium
Materials or lenses bend light to cloak object
If an object is not visible due to not enough photons, what can be done to make it visible?
Use a condenser
If an object is not visible due to the wrong kind of photons, what can be done to make it visible?
Use a detector to detect wavelengths outside of visible spectrum
If an object is not visible due to objects being too small to resolve, what can be done to make it visible?
use a compound lens
If an object is not visible due to an object not interacting with light, what can be done to make it visible?
Use optics
If an object is not visible due to objects interacting with light the same as the surrounding medium, what can be done to make it visible?
Use stains or labels
What do convex lenses do
Refract or bend light to increase the angle which spreads out light making an object larger (slide 9)
How does a compound microscope work?
Light from specimen hit detector
Eyepiece (ocular) lens magnifies image from objective
Condenser lens focuses incoming light
Virtual image that appears to observer as enlarged specimen
(slide 12)
How is magnification on a microscope calculated
Eyepiece (ocular) x objective
What is resolution
Smallest distance at which 2 objects can clearly be distinguished from one object
What determines resolution
How much light is lost between specimen and lenses
How much light is gathered by lenses
Wavelength used for illumination
What is a refractive index
Mismatch between elements resulting in loss of signal between sample, lenses and detector
How can refraction be minimised
Properties of lenses used in air can be adjusted to compensate
Special oil which is the same refractive index as glass to prevent loss from refraction
What is angular aperture of a lens
The angular aperture of a lens is the angular size of the lens aperture as seen from the focal point
(slide 20)
What affect does angular aperture have on microscopy
Higher number = more light = more resolution
What is numerical aperture
number that describes light gathering ability and resolving power of an objective lens
What wavelengths have the highest energy
Shorter wavelengths (also equals higher resolution
What is the resolution for light microscopes
200nm
500nm without super-res techniques
What is the resolution for electron microscopes
2nm
How are specimen on a microscope slide visible
Structures are visible because they interact with light differently from surrounding medium
Many things in cells hard to see without stains or labels
How can you boost resolution
Phase-contrast boost resulting from differences in refracting between cells and cellular structures
DIC uses polarised light to boost contrast from diffraction of light without the sample
What does hematoxylin stain
Nuclei
What does Eosin stain
Eosin
