Posts that relate to the Keyword: contrast

Phase Contrast vs. Bright Field Microscopy

Air is completely transparent, I hope you agree. And water is transparent. If this is indeed the case, then why is it possible to see air bubbles in water? The answer is, that the bubbles have a different refractive index than the surrounding medium, the water. Phase contrast microscopy is now capable of converting a [...]

How to obtain the best resolution with your microscope

The resolution that a microscope is capable of achieving is probably the single most important factor that determines the quality of a microscopic image. Without a sufficiently high resolution, magnification is not possible without loss of quality. There are a variety of different factors that determine the achievable resolution. Some of these factors can not be actively influenced by the microscopist, others can. Some of the factors play a larger role, others a smaller one. In the following post, I want to summarize some of these factors.

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 and excessive heating of [...]

Digital methods for improving microscopic photographs

Digital photography gives the users many new possibilities in improving photographs taken through the microscope. This post gives an overview of the different image processing functions that can be applied to microscopic images. This post places a focus on what is possible, but does not explain the “how” part. This is something that I plan [...]

Increasing Contrast using Optical Methods

Many microscopic specimens are either very thin or transparent or lack color. They lack contrast and can not be easily seen in bright microscope light. In many cases it is not possible or desirable to chemically stain the specimens. In this case, optical techniques become necessary to enhance contrast.

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) and [...]

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.