Answering reader questions

What are the things that all types of microscopes have in common?
Microscopes can be very different (see Different types of microscopes. I therefore limit the answer to light microscopes. Things that optical microscopes have in common include:
Objectives, Oculars/eyepieces, stage (carries specimens), light source, focusing system.

Does glycerol mounting cure?
It will dry only up to a point, but will not (and should not) completely dry out. The glycerol will prevent the complete drying. This makes sure that a certain amount of water remains in the sample. A complete drying of the glycerol mounting medium could result in a shrinking and deforming of the specimen. Algae and other water organisms are especially sensitive to this. It is possible to protect the permanent slide by sealing the edges of the cover slip with nail polish.

Why do electron microscopes produce black and white images?
They produce B/W images because electrons do not have a color. Different wavelengths of light, in contrast, do possess colors that we can perceive. It is possible to artificially color electron microscopic images, however. But this does not reflect the “true” colors of the object.

Is pollen a microbe?
No, pollen are not considered microorganisms (microbes), because they are not capable of reproduction. Pollen do not divide to form more pollen. They form sperm cells for fertilizing the plant’s egg cell.

Why does the smell of hay infusions decrease over time?
As a hay infusion ages, different microorganisms start to grow (and others start to die out). Different microorganisms produce different substances which are responsible for the smell.

Is a bacterium too small to be seen under a compound microscope?
No, most bacterial can be seen with compound light microscopes from magnification of 400x up. If the resolution of the microscope optics is not very good, then it will be difficult to see them. You need phase contrast optics to be able to see bacterial well. They may be difficult to see using regular bright-field optics, because bacteria are transparent. Alternatively one may need to stain them. Beginners may have problems distinguishing bacteria from small specks of dirt and dust.

Which type of microscope would be best to use if you wanted a 3-Dimensional view of a virus?
Compound light microscope: It is not possible to see viruses with these microscopes. Resolution and magnification are not large enough.
Transmission electron microscope (TEM): It is possible to see viruses with TEMs, but they provide 2D views.
Scanning electron microscope (SEM): These are the ones that are able to visualize viruses in 3D

Why is it important to apply a cover slip at a 45 degree angle when making a wet mount?
Applying the cover slip at an angle (instead of dropping it down flat on the specimen) pushes the air to the side and therefore minimizes the risk of air bubbles.

2 thoughts on “Answering reader questions”

  1. I want to buy an Olympus darkfield condenser compatible with the CH-30 RF200 model.Can you help me please,any information on this would be gratefully received.Thank you.

    1. Hello, for simple darkfield work, a dedicated condenser is not needed. There are 3 ways to obtain darkfield:

      a dedicated condenser: expensive, best performance for a wider range of different magnifications.
      a home made patch stop: cheapest
      a bought patch stop: reasonably cheap, saves work but has same performance as home made version

      This patch stop can be placed into the regular filter holder of the bright-field condenser. Read this post for more information on how to make a patch stop. Try black cardboard etc. If you are already certain that you need a dedicated condenser, then I would look for one in Ebay or I’d contact a local Olympus dealer. Be careful, there are different standards. Olympus (like many other manufacturers) started to move away from the traditional “finite” optics to the more modern “infinity” systems. Be careful that the condenser that you buy is one that is for the 160mm finite system. Check the objectives of your microscope. If they have “160” printed on them, then then condenser must be for the finite system. These ones are becoming rare and also expensive, unfortunately. The item designation for a finite system darkfield condenser is: BH-DCD. I did a quick search and found out that these condensers cost more than $500. The item designation for a commercial patch stop for Olympus is CH2-DS (about $12 in Ebay). There are also other condensers around, ones that also allow for phase contrast work, besides darfkield and brightfield (CH2-PCD), but the built-in phase contrast filters are useless unless you have phase contrast objectives. Summary: if you are an amateur and like to experiment with darkfield, then a patch stop may offer the best price/performance ratio. It also offers the advantage that you can experiment with different patch stop shapes, and even colors.

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