Module # 2 - Microscopy Flashcards
Convex lens
Thicker at the centre, causes light rays to converge, used in microscopy.
Concave lens
Thinner at the centre, causes light rays to diverge.
Parallel light rays
Are caused by convex lenses and make distant sources converge at a specific point.
Focal point
The specific point at which light rays converge.
Focal length
The distance from the centre of the lens to the focal point. The more the lens is curved, the shorter the focal length.
Focal plane
The vertical plane the focal point lies within.
Working distance
The distance from the specimen to the objective sense. high magnification objectives have a shorter working distance.
Depth of field
The range at which an object is in focus.
When an object is located a great distance from the lens, greater than two focal lengths, the resulting image will be:
Real, smaller and inverted.
When an object is located exactly two focal lengths from the lens, the resulting image will be:
Real, same size and inverted
When an object is between one and two focal lengths from the lens, the resulting image will be:
Real, magnified and inverted (most microscopes have this property.)
When an object is located exactly one focal length from the lens, the resulting image will be:
Parallel. No image is produced.
When an object is brought within one focal length from the lens, the resulting image will be:
Virtual, magnified and erect not inverted. Can only be visualized by looking through the lens. How oculars work on a microscope.
Total magnification
Is the combination of the ocular and objective lenses magnifying an image (e.g. 40X objective used with a 10X ocular lens is a total magnification of 400X.)
Chromatic Aberration
Produces a distortion in the colours of the image, may also produce a fringe of colour around the periphery of the field of view. Occurs when each wavelength of light has a specific focal point. Alternating convex and concave lenses in the objective can correct an chromatic aberration.
Spherical Aberration
Light passing through the centre of the lens does not bend as much as those rays passing through the periphery, resulting in a blurred image. Happens most often when the magnification is higher.
Achromatic lenses
Used to correct chromatic aberrations. Least expensive option. Corrected for two colours (red and blue.)
Semi-apochromats (fluorites)
Involve incorporating fluorite into the composition of the lenses to correct for red and blue, with some correction for green light in chromatic aberration.
Apochromats
Most expensive corrected lenses. Corrects all three colours; red, green and blue.
Plan-achromats/Plan-apochromats
Correction for spherical aberrations.
Light source
Light source for a microscope. Tungsten or tungsten halogen bulbs are usually used. LED bulbs are more expensive but also have a longer lifespan. An adjustable radiant field diaphragm is located above the light source to control the diameter of the light directed onto the specimen.
Condenser assembly
Acts to focus the illuminating light onto the slide on the stage. An adjustable aperture diaphragm controls the angle of the cone of light reaching the specimen.
Kohler illumination
Used to make sure the condenser provides proper illumination onto the specimen. Results in an even distribution of light to illuminate the slide. Provides a nice even light, angle of cone of light matches the NA of the objective.
Stage assembly
The stage is where the slide is placed to be viewed, and is held in place by a slide holder. Slide controls move the stage in a horizontal plane. Focus knob controls the movement of the stage in a vertical plane. Corner scales can be used to note the particular location of an object on the slide.