Not every object is suitable for observation with a compound microscope. Many specimens are either too large, too thick or simply too dark. If you want to look at an object with a compound microscope, then you must make sure that the object is sufficiently thin, that it allows light to pass through and that it has sufficient color contrast. Let us have a look at these points in more detail.
- Thin: the specimen must be sufficiently thin to be placed on a slide with a cover glass on top. Specimens that are thick will not allow much light to go through and you will only see a dark blob without much detail.
- Translucent: The specimen must allow light to go through (it must be translucent). Specimens that are too dark can be bleached to make them brighter. There are several ways to do this, but this requires the use of chemicals and some laboratory work.
- Contrast: The specimens must show sufficient color contrast. Some objects, such as bacteria, are both sufficiently thin and do allow light to go through. Still, they can be quite difficult to see because they do not have enough color contrast to the background. They are as clear and colorless as the water that surrounds them. Specimens like these can be made visible by staining them. There are some more specialized microscopes (so-called phase contrast microscopes) which do allow the observation of these specimens, but they are more expensive.