Bright field compound microscopes have been taking their place in the field of microscopy. This type of microscope has the feature of having a bright light. It uses this light in a direct manner without any manipulation needed. Some examples include low power stereoscopic microscope and microscopes used for dissection.

In the subject of bright field microscopy, light is obtained from underneath. A typical kind of light used in this case is the halogen microscope bulb. This bulb focuses the light in a condenser, which is called a bright field light condenser. These condensers can be expected from those bright field compound microscopes with better quality.  Usually, condensers are placed on a rack and pin down gears, also with the use of a Koehler field diaphragm, to help in proper focusing of the specimen.

Another essential factor on the use of a bright field compound microscope is its suitable illumination of the examined specimen. This is basic in attaining a Koehler illumination. In this case, the light path is inserted with regular colored filters. Basically, its light source is from the bulb. It collects light from the base and focuses with Koehler illumination using a bright field condenser. Then, the light is transmitted to the specimen, which is located on the microscope slide.

Below is a detailed illustration and typical procedure on how a bright field compound microscope works.

•    With the bright field microscope, a 4x objective is used in scanning. The light is turned on and the specimen is taken and inserted at the center. An iris diaphragm is used to pin down when you opt to start focusing on your specimen. When using this objective, it must always be remembered that, optically speaking, it is different from other objectives. It has a different resolution compared to the other ones. Its basic purpose is only to have a view of the specimen. When viewing the entire field, set the light condenser lens at low so that the beam of light is widened. Although the light source can be used in any level of intensity, it is advised that a low magnification is utilized when using this type of microscope. If the specimen is properly centered, you can notice some glow from the light given by the condenser. Now if the specimen is already focused properly, selecting other objectives can then be started to get a clearer view of the specimen. In doing this, the fine focus is always used.

•    In selecting another objective, it is wise to start with 10x. You may choose a higher one, too to give more focus of the specimen as most microscopes allow you to set a particular objective and focus the specimen at a certain point. Still, what is needed is only the fine focus when shifting from one objective to the other. If you choose to set up the microscope for Koehler illumination, you can do so by using the same range.

•    A limit in the field aperture should be set. Most apertures or openings are built into the microscope’s base. This allows reducing the light from coming into the optical pathway. Also, this enables the user to put the condenser at the level where there is the highest illumination. This is the point where Koehler illumination becomes very important as the light condenser is able to provide vertical beams of light.

•    The field edges have to be directed using the condenser lens. At this point, it has to be certain that the aperture and the specimen are focused at the same time. In this instance of Koehler illumination, the light condenser should be set to a particular point. This can be done when the specimen is focused using 10x objective or even greater.

•    Using the condenser knobs, illumination has to be centered. The knobs are then used to adjust the illumination in either directions or into the middle of the field. The aperture has to be opened just ahead of the field edges so that the condenser illumination can be precisely re-centered again.

•    The iris diaphragm has to be set to the greatest resolution. Light levels are adjusted using the intensity knobs. It is all up to you on how you would like to determine the level of contrast that you need in viewing the specimen. Practically, a diaphragm has to be set to the greatest level of resolution and light intensity has to be within comfortable degree. This is required for all objectives to be used.

•    An adjustment on the eyepiece has to be considered in relation to the distance. There is much variation on the distance in every human eye. It is important to adjust the eyepieces for the images to blend together.

•    When a high power objective of 40x is chosen, it is vital to use the diopter correction, which is located underneath the eyepieces. Bright field compound microscope has to be adjusted explicitly for every person using it. This is the sole purpose of the diopter correction. It has to be certain that the scope is set at the firmest depth of field or greatest resolution. High power is typically used at this point and when the user needs to set the depth of filed and contrast, the iris diaphragm has to be used.