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dark field bright field microscopy?

These are  different microscopic techniques.

  • Bright field microscopy is the conventional technique. It is suitable for observing the natural colors of a specimen or the observation of stained samples. The specimen appears darker on a bright background.
  • Darkfield microscopy shows the specimens bright on a dark background. Brightfield microscopes that have a condenser with a filter holder can be easily converted to darkfield by placing a patch stop filter into the filter holder. The specimens appear brigh, because they reflect the light from the microscope into the objective.
  • If one have the diffraction field of a perfect (or homogeneous) medium, he can see the image of a perturbation, making the perfect field lower or higer. If the homogeneous field is lower but the perturbation image intensity is higer, we have dark field image. When the homogeneous field has hihger intensity and we see the image of pertutbation as local decreasing of the intensity, we have bright field image.

 

Bright field and Dark field microscopy

To learn about how dark field microscopy differs from bright field microscopy and to see some images of mosquitoes taken in dark field mode, read on.

Bright field (transmission mode) microscopy is an older and very powerful form of microscopy. It is the most common, and is the only type available on most non-research-grade microscopes. In bright field, a light below the sample illuminates the specimen as the microscopist looks down from above, and the light from the light source is transmitted either through the specimen or directly into the objective. The light that hits the specimen is selectively passed through and/or refracted, so it looks colored. (If the specimen is opaque, no light passes through and the specimen just looks black.) In bright field the background (the field) is bright white because the source light is bright white and it hasn’t passed through anything to change its color. Bright field microscopy works best for samples which are thin enough to be transparent or translucent. For instance, stained cells show up very well. Click to see a bright field microscopy gallery.

In dark field microscopy the specimen is not illuminated at all by light shining through it to the objective. Bright field microscopy uses a condenser lens between the light source and specimen stage to focus light on the sample, but in dark field mode, a special condenser lens is used (or an opaque light-blocker is put in place above a normal condenser lens) that blocks all the light that would normally radiate directly from the light source into the objective. The lens scatters light from the source and lets oblique light through, and that light hits the specimen from different angles and scatters and refracts and reflects onto new paths that can reach the objective lens. Thus, in a dark field image, the background (field) is dark, because there’s nothing in the background for oblique light to reflect off of in order to get to the objective. Only the specimen is illuminated.

In dark field images, the specimen usually appears in false color. The edges of features are usually visible in high contrast and resolution. Bright field and dark field microscopy are complementary: many specimens that are not well imaged in bright field are well imaged in dark field and vice versa.

Dark field microscopy, explanation and breakdown of types
Dark field microscopy (Rice University)
Wikipedia on bright field microscopy
Parts of a microscope
The specs of our microscope in the film, a Morphologi G2 from Malvern Instruments

Photos of mosquito bits from the morphology microscope:
Ommatidia (parts of the compound eye) of a mosquito
Fringes on the edge of a mosquito wing
Various sensillae on a mosquito wing vein
Fringes on a mosquito wing vein
Fringes on a mosquito wing vein

Transcript of Bright field and Dark field Ilummination

Bright field and Dark field Illumination
Dark field Illumination Microscope.
Dark field illuminated picture with labeled Microscope.
Dark field Illumination Process.
Where is Bright Field Illumination used?
Schools
Microbiology and Bacteriology

Difference between Dark and Bright Field Illumination.

Bright Field and Dark Field Lighting


Understanding the “W”:

  • Reflected: light is the same angle as the source
  • Bright field: light is reflected into the camera
  • Dark field: light is reflected away from the camera


Bright Field Lighting:

  • Good for high contrast but specular reflections on shiny or reflective surfaces
  • Rule of thumb: Light should be twice the field of view at the camera lens
  • Avoid “hot spots”: Diffused light source provides even illumination in the brightfield


Dark Field Lighting:

  • Diffused light is reflected into the camera; specular light is reflected away
  • Light source is outside the “W”
  • Light is reflected away except for textured surfaced and elevation changes

 

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