How Does Brightfield/Darkfield Light Microscopy Works?
The principles behind brightfield/darkfield light microscopy are relatively complex. In essence, they are the concepts that allows the users to have a better view of the specimens that they are observing.
A bright field microscope is a microscope that gets light source from below. What it uses for this purpose is a halogen bulb. A simple bright field microscope is equipped with a mechanism that directs the light into the condenser. Higher quality bright field microscopes have enhancements in aid of this feature such as condensers that are connected on rack and pinion gears. There are also other models that are equipped with diaphragms so that users can properly focus of the light on the sample that is being examined.
When a microscope is said to be a brightfield microscope, it would mean that it is equipped with an illumination system that is a notch better than that of a standard microscope. But these days, brightfield microscopes generally indicates the normal mode of viewing specimens. This is all due to the advancement of microscopy. To be on the safer side when buying microscopes though, it is best to check out the microscope’s specifications and determine whether it is particularly indicated in there that the device is indeed a brightfield microscope.
A dark field microscope works a little differently. It manipulates the microscope’s light source by placing a diaphragm that looks like a disc right inside the path of light. Thus, the specimen becomes illuminated through a series of scattered light. In dark field microscopy, the condenser is used to form a hollow cone of light and the objective lens is made to sit in the darker part of the hollow cone produced. Therefore, the entire viewing field looks dark if there is no specimen placed on the microscope’s stage. The concepts behind dark field microscopy is the one most commonly used for transparent specimens.
Now brightfield/darkfield light microscopy combines the two technologies in one device. These are the microscopes that support the two lighting systems together. As result, users can switch from one mode to the other with a mere flick of a button. Bright field light microscopy is best used for regular specimens. Plant leaf samples, small insects, and similar objects are best viewed under it.
Dark field microscopy, on the other hand, is best used for viewing uni-cellular organisms that are transparent in nature. Using dark field microscopy spares its users the job of staining the specimen prior to viewing them. With a microscope working in dark field mode, all a users have to do is to mount transparent living cells on the slide and view it. No need to apply a drop of dye, which is yet another skill to master.
This makes a brightfield/darkfield light microscopy the best option for students and novices. Professionals, because of their substantial experience, can readily determine if the sample they are going to view is transparent. But not all students can do that just yet. With a brightfield/darkfield light microscope though, they can easily toggle to the right lighting system without much of a hassle. They can accurately view their specimen even if they don’t know its nature.
To do its job, a brightfield/darkfield light microscope is equipped with three mirrors. Two of them are axicon mirrors and one is a plane mirror. One open shutter directed on to the light beam as provided by one of the mirrors will produce brightfield illumination. The same principle applies for dark field.
The only notable disadvantage of a brightfield/darkfield light microscope is that it cannot be used with computer controlled systems. Switching between the modes of operation requires human intervention. It is not yet possible to remotely control brightfield/darkfield light microscopes. There isn’t a system developed to do just that as of this time.
And because the microscope support two types of illumination system, it was observed that it has limited performance when it comes to using its own lighting sources. A dark field mode requires more light than the bright field mode, therefore the performance of the microscope, in terms of magnification abilities, vary when users change from one mode to another.
Basically, this is how brightfield/darkfield light microscopy works. A dual mode microscope poses to be a good option, but always consider how you intend to use the microscope. If you are not going to view transparent specimens at all, or if you are fine using a dye for that process, you might want to settle for a brightfield microscope and save the difference.