Basic Light Microscopy Flashcards
Quiz 1 Start from the basics of light and microscopes
What techniques are standard for analysis of Trace Evidence?
- polarized light microscopy (fibers, minerals)
- comparison transmitted light microscopy (hairs, fibers)
- index of refraction measurements (glass, fibers)
What techniques are standard for analysis of Drug Analysis?
- crystal tests
What techniques are standard for analysis of Forensic Biology?
- crystal tests for hemoglobin
- identification of sperm
What techniques are standard for analysis of Firearms examinations?
- comparison reflected light microscopy (bullets, cartridges, took marks)
What techniques are standard for analysis of Questioned Document Examination?
- reflected light microscopy of handwriting and printing
What are some examples of hyphenated microscopic methods?
- microspectrophotometry
- micro FTIR
- micro Raman
Who invented the 1st microscope? i.e. Father of Microscopes
Zacharias Janssen 1590
What was Robert Hook’s contribution to science?
- developed and used a compound microscope to observes cells in cork in 1665
What was Van Leeuwenhoek’s contribution to science?
- developed a simple microscope with very good lens to examine small organisms
List the type of Lens Aberrations
- chromatic aberration
- spherical aberration
- coma
- astigmatism
- curvature of field
- lateral color
Define Chromatic Aberration
- caused by the variation of refractive index with wavelength for a lens material
(this doesn’t happen with curved mirrors) - the wavelength dependence results in slightly different focal lengths for different wavelengths of light
(creates a “rainbow” around image)
What can counteract Chromatic Aberration?
- achromats (compound lenses) can reduce or eliminate the problem
- components are chosen such that some of the variation in RI as a function of wavelength cancels out
Define Spherical Aberration
- a loss of definition in the image arising from the surface geometry of a shperical mirror or lens
- results b/c the actual focal point of a light ray depends on its distance from the optic axis
(there are multiple focal points causing the imagine to be partially clear)
Define Coma
- caused by the distortion of a wavefront as it encounters a lends asymmetrically (distortion of how light hits the lenses)
- light rays farther from the optic axis have severe aberration and the resulting image looks like a comet-shaped series of circles
Define Astigmatism
- a defect in lens caused by a deviation from spherical curvature
- results in distorted images, as light rays are prevented from meeting at a common focus
- result is two line images at different points in space
Define Curvature of Field
- causes a flat object to appear sharp only at certain parts instead of being uniformly sharp
Define Lateral Color
- causes “colors” to focus at different distances from the image center
- most visible near corners of images
- a point source of white light is imaged as a small solar spectrum
Define Plan
- stands for flat field
- lenses which are uncorrected for flatness of field will have the center of the field in focus and the outer edges out of focus
(or vice versa depending on how you focus the lens)
What are Achroplans?
- a type of objective lens
- corrects curvature of field
- best for transmitted light
What are Epiplans?
- a type of objective lens
- corrects for curvature of field
- designed for reflected light use
What are Achromat lenses?
- lenses that have good color correction for 2 wavelength of light
(they are easy on the wallet)
What are Planachromats?
- achromats with correction for flatness of field as well as color correction at 2 wavelengths
What are Plan-Neofluar lens?
- semiapochromatic lenses
- have good color correction for at least 3 wavelengths & also have flatness of field
- excellent for polarization microscopic techniques i.e. differential interference
- excellent lenses for all types of fluorescence microscopy (transmit UV very well)
- contains fluorite elements making it good for fluorescence work
What are Apochromatic (planapochromat) lenses?
- the most higly color corrected objectives
- corrected for 4 wavelengths and are top of the line in objective lenses
- most often have the highest numerical apertures
- do not transmit UV light
- work very well for visible light excitation in the blue and green ranges