Posts of the Category: Techniques

Here I explain the handling of the microscope and different methods to enhance contrast.

Köhler illumination to reduce reflections

The Köhler (or Koehler or Kohler) field diaphragm is located above the light source. It is responsible for controlling the width of the light beam (but not its intensity). The light source of a microscope without Köhler illumination will illuminate the whole specimen, which may be the source of stray light [...]

How to make microscope filters

Commercial microscope filters are usually made of stained glass. In the case of patch stops (as used in dark-field illumination), they may be made of aluminum. The dark-field patch stops block some of the light and the specimen will appear bright on dark background. The traditional way of DIY patch stops is cutting them [...]

Bacteria in phase contrast

The four pictures on the right show different bacterial species in phase contrast.
About phase contrast
Bacteria are transparent and therefore difficult to see using regular bright-field microscopy. The bacterial cells will appear just as bright as the surounding medium and there is no color contrast. Phase contrast optics provides a solution. Phase contrast optics convert [...]

Digitizing photographic slides with a digital camera

Several years ago, at a time when digital single-lens reflex (SLR) cameras were still financially unobtainable, I used slide film to document my microscopic observations. These slides are now sitting, more or less nicely sorted, in a folder, doing pretty much nothing. I don’t even have a slide projector [...]

Potato Stach Grains

Here I would like to show you two images of potato starch grains taken with different optical contrasting methods.

Drawing Microscopic Images

Drawing is still a useful method for documenting microscopic specimens, despite advances in (digital) imaging technologies. There are certain advantages in drawings that photographs do not possess.

Enhancing Photomicrographs

There are a range of different possibilities:

Enhancing contrast: Photo editing software (such as Adobe Photoshop or GIMP) contain functions that enhance the contrast of an image. Find the menu point “Auto Levels” or simply “Levels”. This tool will make the darkest part of the image black (even if it was not black before) [...]

Oblique Illumination

Oblique illumination is a contrast enhancing technique which can be realized with the use of home-made filters (patch stops) placed into the filter holder of the microscope condenser.

Darkfield Microscopy

Darkfield microscopy is one of the simplest and cheapest contrast enhancing techniques. It works well for specimens that have a refractive index which is different from its surrounding medium, but which are difficult to see because they lack color. Dark field microscopy shows the specimen bright on a dark background.

Working with the condenser aperture diaphragm

The condenser aperture diaphragm (or iris diaphragm) is used to control the contrast and resolution of an image. This article explains the usage of the diaphragm.