Tuesday, August 16, 2011

Microscope Filters Explained

Microscope Filters are used for both observation and photo microscopy. Below are some common filters and their intended use.

  • Green Interference FilterAchromat and planachromat microscope objectives are best corrected spherically for green light, which means their performance improves with the use of a green filter. Phase contrast objectives are also created to give the best phase images in green light.
  • Daylight Blue Filter: This filter is for observation use only. It provides a pale gray-blue hue to the field of view and is often used to balance the light created by tungsten or halogen light sources. The daylight blue microscope filter was not created for use with photomicrography with daylight color film. Daylight color film requires a blue conversion filter that will boost color temperature of the light source and simulate light of daylight color temperature quality required for daylight balanced color film.
  • Ground Glass Filter: This filter is often placed over the illuminator to give a more even and diffused light. It is often used with Tungsten illuminators.
  • Neutral Density (ND) Filter: This microscope filter is used to reduce the light by a percentage. There are different numbers listed on the ND filters - such as ND8 or ND50. ND8 means that the light is reduced by 8%. Neutral density filters are often used in photomicrography.
  • Didymium Filter: This filter is also known as an “enhancing filter”. The didymium filter is made of didymium glass for increasing the intensity and saturation of red objects.  Since thin sections of biological tissue are often stained with one or more dyes to enhance visibility of various features in the specimen, if taking photographs of these specimens, it is desirable for the stained colors to appear in the picture. While most stains show up well on colored film, there are several that appear washed out. A didymium filter helps combat this problem.
  • Yellow Filter: The yellow microscope filter is commonly used to fine-tune the color balance of tungsten and halogen microscope light sources for photomicrography with color film. There are several metallurgical applications where the yellow filter is helpful in identifying failures in metal structures.