Posts of the Category: Techniques
Here I explain the handling of the microscope and different methods to enhance contrast.
The hemocytometer (counting chamber)
The hemocytometer (or haemocytometer or counting chamber) is a specimen slide which is used to determine the concentration of cells in a liquid sample. It is frequently used to determine the concentration of blood cells (hence the name “hemo-”) but also the concentration of sperm cells in a sample.
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.
Cover glass thickness and resolution
The thickness of the cover glass can have a significant impact on the resolution. The effect is highest with high-numeric aperture aperture (high magnification) objectives, and barely noticeable when using objectives of a low numeric aperture. Types of cover glasses Cover glasses come in all sorts of different sizes. I already wrote a post about [...]
The effect of the mounting medium on specimen and image quality
The mounting medium can have a significant effect both on the image quality and on the specimen itself. I tried a little experiment by observing pollen from a plant (in this case the buttercup, Ranunculus), mounted in five different ways: Air-mounted, with no cover glass Air-mounted, with a cover glass Mounted in water (temporary mount) [...]
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 [...]
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 out [...]
Bacteria 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 the differences in optical density (i.e. the refractive index) of the bacterial [...]
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 to look at them. Evidently the [...]