CONDENSER – This is the lens assembly that sits underneath the stage and focuses light through the specimen to the lens objective. Abbe condenser (named after Ernst Abbe who worked for Carl Zeiss in the late 1800’s) is the standard brightfield condenser which focuses light for 4x to 100x objectives. For objectives less than 4x power, an additional “swing out” condenser is typically required to get a full field of view at the lower magnification.


Dark field is the method whereby the sample being viewed is actually in front of a dark background and light is being angled onto the sample from the sides.

Under phase contrast conditions, the light coming through the specimen is shifted into two beams, one slightly out of phase with the other. This gets a little complicated to explain easily, but as far as equipment concerns, you need two matched items in order to get phase contrast. You need a phase annulus, and the matching lens objective. For instance, if you want 40x magnification phase contrast microscopy, you need a 40x phase lens, and a matched 40x phase annulus. If you want 100x phase, you need the 100x lens and the matched 100x phase annulus.

Both the techniques of darkfield and phase contrast allow nearly invisible microorganisms within the blood to be "lit up" and seen. It also clearly delineates the blood cells. This method is in contrast to the standard microscope "brightfield" conditions where light shines directly through the viewed sample, and invisible particles remain invisible.

DARKFIELD STOP – Typically this is a round disk that fits up into an Abbe condenser, or rotates into place with a turret condenser. The disk is solid/opaque in the middle (no light can pass through, while not being so large as to block light completely from passing around the perimeter. When viewing through the microscope, this gives a darkfield image. Because it was not designed with exacting criteria for optimum darkfield imaging, it is a low cost way to get a darkfield representation.

DIC – Differential Interference Contrast (In Dry Layer blood work it means Disseminated Intravascular Coagulation – but that’s another topic.) DIC is a method of altering light through a specimen to render a 3 dimensional perspective.

FILTER HOLDERS – Exactly as the name implies. This is a piece that typically will snap into or rotate under a brightfield condenser.

A typical use would be a blue filter when using low levels of light in a brightfield application. (Like dry layer blood analysis.) When low levels of light are used, you usually get a yellowing effect because the lamp is turned low. The blue filter brings the light back to a more natural white light.

Another application would be using a green filter for phase contrast. Because of the wavelength of light, using a green filter will give higher resolution for phase contrast. In live blood applications, the higher resolution is not discernable through video viewing, and most find that it is not as appealing to view as without the filter.

INFINITY CORRECTED OPTICS – Most specimen lens objectives will have a fixed optimum point of focus, such as 160mm from the rear aperture of the lens. In this case, photo tubes and eyepieces that are put onto the microscope will have a focus point 160mm in distance from the objective. This is called a finite corrected optic. An infinity corrected lens projects an image that is collimated to infinity, and the image is brought into focus at the point of the eyepiece (head assembly), or the photo tube through the use of a convergence lens. Infinity correction becomes a consideration if you’re going to be swapping multiple apparatus between the body of the scope and the head assembly. Today infinity correction is almost always found on high level clinical and laboratory microscopes. Biomedx uses infinity corrected optics on all its scopes.

KOEHLER ILLUMINATION – Gives a stronger collimated  light from the lamp through the specimen objective. Only pertains to brightfield applications – it is inapplicable to phase contrast and is only used for darkfield when using some turret condensers to eliminate incident light and increase contrast.

LAMP – As in light bulb. The illumination system. In many scopes this is a tungsten or halogen light bulb. Usually ranging from 20 to 30 watts. This is sufficient for all brightfield and most phase contrast work. However, it is insufficient for high quality darkfield or when using high magnification optical zooms systems. This is where a separate lamp house (special enclosure housing a high wattage bulb) needs to be used. This unit usually sits behind the scope and the light gets focused through to a mirror assembly which directs it up through the condenser and specimen being viewed.

N.A. / NUMERICAL APERTURE – In theory, microscope magnification could be increased to almost infinite levels, but magnification in itself is meaningless unless the image is sharp. The decisive factor in determining the distinctness of the image is the resolving power of the objective. The resolving power, in turn, is determined by the numerical aperture of the objective. The N.A. value actually represents the brightness and the resolving power of an objective, and corresponds to the relative aperture (the F-number) of a camera lens. The higher the N.A., the more resolving power of the lens.

NOSEPIECE / OBJECTIVE TURRET – This is actually the rotating turret that holds the objectives, and it sits right under your nose when your looking through the microscope.

OBJECTIVES – These are one of the most important elements to the microscope - the optical lens which screw into the revolving nosepiece and magnifies your specimen. Objectives can be divided into two basic types according to their degree of axial chromatic compensation. (Axial chromatic aberration occurs when light composed of a number of wavelengths is not focused at one point on the optical axis, but instead, is focused at a number of different points according to differences in wavelengths. The performance of an objective depends greatly on the degree to which it compensates for axial chromatic aberration.) Here we find achromat and apochromat objectives. Ach lenses compensate for red and blue color aberrations, and apo lenses go further and also compensate for blue-violet. Achromat have seen wide use because of their low cost, and apochromat typically are in the domain of research, as some single apo lenses can range in cost from $1200 to $8000.

PHASE ANNULUS – The optical light guide for phase contrast microscopy which sits just below the condenser lens, usually by rotating into place with a phase turret condenser, or snapping into place as with an Abbe type condenser. Zernicki phase contrast refers to the person that developed it, and it means that the x-y axis of the phase annuli can be maneuvered for optimum imaging. This is in contrast to what is called slider phase, whereby the phase annuli is actually slid into place under the condenser and is fixed once slid in. No fine tuning is possible.

PARFOCAL – Relates to the ability of an image to stay in focus in two places at the same time. For instance, if you looked at a specimen in the microscope that was in perfect focus, and your video system was parfocal, you could look at your video picture and it would be in perfect focus along with the image viewed through the eyepiece.

STAGE – This is the platform where the glass specimen slide is positioned. Most clinical scopes will have a left or right handed stage adjustment mechanism which positions the specimen slide along the x-y axis.

TRINOCULAR HEAD (BINOCULAR/MONOCULAR) - This is the assembly that the eyepiece objectives fit into and allows you to peer at your specimen. Tri – means there is a space (or tube) for two eyepieces and a third tube, usually on top, that can hold another eyepiece, or more typically a photo camera, video assembly, etc.

TURRET CONDENSER – A condenser that is multipurpose in design for convenience, in that it can be a standard brightfield condenser, and with the rotation of a turret assembly under the lens, different phase annuli, filters, or darkfield stops can be easily rotated into place.

X Y Z AXIS - In front of the microscope with a specimen on the stage, the X axis is the left/right movement, the Y axis is the forward and back direction, the Z axis is the vertical or up and down direction of the stage.

The axis control arm on the right or left side of the stage controls the slide speciment on the X/Y axis, the stage focus knobs controls movement on the Z axis.

Scope Terminology

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Terminology of parts and more on microscopes for live blood cell analysis and dry layer analysis, including dental gingival screening.

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