Posts of the Category: Theory
These posts have a more theoretical approach to the subject matter. It provides a basic overview of microscope optics.
Microscopic observation of EHEC?
Is it possible to use microscopes to identify pathogens, such as the EHEC bacterium, which currently (May-June 2011) causes problems in some parts of Europe? The answer is, unfortunately, no.
How many cells are there in the human body?
“How many cells are there in a 9-year old tree, in a flower and in an elephant?” – I was asked this question recently by an elementary school teacher, and I, as a biologist, should naturally know this answer. The students found out, by research, that the adult human body contains an estimated 10 trillion [...]
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 [...]
Answering Reader Questions
Why is refractive index of mounting media important? The refractive index is important for several reasons. First, it influences the resolution of the image. Second, if the refractive index of the specimen is too similar to the refractive index of the mounting medium, then it may be difficult to see the specimen if it is [...]
Life in the Flower Pot Water (or: Comparing the Size of Prokaryotes and Eukaryotes)
Over the past few years, I’ve met several students who wanted to see bacteria through the microscopes that we have at school. Unfortunately, these devices are not equipped with phase contrast optics. The transparent bacteria are therefore difficult (but not impossible) to see. The biggest draw-back, however, comes from a different source: some of the [...]
Euparal Mounting Medium
Euparal is a semi-synthetic mounting medium used in microscopy. It is slightly yellowish in color, flows well and cures after a few days. After curing, it becomes very hard but not brittle, keeping elasticity. Euparal also adheres strongly to glass. It has a refractive index of 1.5174. Compared to other mounting media, Euparal has 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.
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 [...]
