It should be pointed out that many of these terms have a much broader meaning than what is described here. For the purposes of this document I will define these terms as they apply to amateur light microsopy.

Achromatic
This means that different colors focus at the same distance. When lenses are not achromatic different colors focus at slightly dfferent distances. This makes it impossible to get a precise focus. This also causes the colored fringes charactheristic of a "toy" microscope and other low quality optical instuments. All lab quality optics are achromatic, and may have other characteristics as well, such as Plan or SHC.

B.F. Bright Field
This is the the normal mode of Substage lighting in which the field, or empty area, around the subject is bright, ideally bright white. See Dark field.

Binocular Microscope
This describes a microscope with two eye pieces arranged so that you can look into it with both eyes. Stereo microscopes will be binocular but binocular microscopes are not necessarily stereo. Note that if the second eye piece is not arranged so that you can look into both at the same time (off at an odd angle) it is usually called a "multiview" or "teaching" microscope.

Coaxial Fine Focus
A coxial fine focus is located on the same axle as the coarse focus and is capable of adjusting over the entire range of focus. The main advantage to coaxial fine focus is that it can reach the focal point no matter where the coarse focus is set. If the fine focus knob is on a separte axle it will usually have a limited amount of movement and if it can't reach the focal point you will have to re-center the fine focus, re-adjust the coarse focus, then re-adjust the fine focus. That can be a real pain! It isn't surprising , then, that coaxial fine focus is a coveted feature.

Color filters
Often used in a special filer holder attached to the condensor, filters can bue used to correct the color bias of the light source. The yellowish color of a halogen light, for example, can be corrected with a blue filter.

Compound Microscope
Literally this means a system with 2 or more lenses or sets of lenses. This usually refers to a biological or high power microscope, as opposed to a stereo other low power microscope. This term is not entirely accurate, since most stereo and other low power microscopes also have both ocular and objective lenses.

Condensor
This is a device that "condenses" or focuses the light. Special types of condensors are used for Dark Field and Phase Contrast work. Most condensors have a filter holder for color filters or perhaps a polarizer.

C.S. Cross Section
This describes a thin slice that is cut across an object thus giving a flat section that is fairly translucent, and thus ideal for microscopic examination. The shape will be a 2 dimensional version of the orginal shape. Thus a solid cube would become a solid square, a hollow cube would be a hollow sqauare, a rod would be a solid cirle and a tube wold be a hollow circle. If you look at the top of a stump from a tree cut straight across, you'll see what a cross section of a tree would look like.

D.F. Dark Field
This describes a technique used with substage lighting where a spcecial condensor is used that prevents light from entering the lens directly, thus the field is dark. The subject seems to glow. This gives unique contrast characteristics to certian translucent subjects, but , like Bright field, works only with translucent subjects. For opaque objects, Super Stage lighting is used.

Epi Fluorescence
This is a specialized form of super stage lighting which uses a special lighting fixure mounted on the head of the microscope along with special filters and special objectives. The filters are "color exicting" and give the subject a unique dazzling glow. The images produced with this technique are very impressive! This is an advanced and very expensive technique rarely used by amateur microscopists.

Eye Piece
Also known as "ocular", the eye piece is the part of the microscopoe that you look into. The power of the eye piece is multiplied by the power of the objective to give the total magnification. Most Lab quality binocular microscopes have interchangeable 10X and 16X lenses. Thus, a 40X objective can give either 400 or 640 power depending on which eye piece is used.

L.S. Longitudinal Section
This is a thin slice taken vertically. This is good for showing the long structural cells in a plant stem.

Mechanical Stage
This is a special stage, built in or added on, that moves a specimen around and is controlled by knobs. It replaces the slide clips used on a standard stage. Mechanical stages give much smoother and more precise control than what could be achieved by moving a slide by hand. Graduated mechanical stages can be used to make fairly accurate measurements.

Metalurgical Microscope
This is a miroscopoe fitted with a lighting fixture on the head and special objectives featuring openings that allow light to shine through the outer rim and onto the object. These special "scopes" are called this because they are often used with metal specimens though they work well with other opaque objects such as mineral specimens and whole, sometimes live, insects. They are usually limited to 400 power. These are specialized microscopes that are often quite expensive but some models sell for less than $1000.

Monocular Microscope
This describes a a microscope with a single eyepiece. Most "toy" microscopes are monocular, but, though quality microscopes are more often binocular, monocular microscopes are not necessarily toys.

N.A. Numerical Aperture
The technical definition involves angles and refraction and is kind of hard to grasp if you're not a physicist. What it amounts to, from the view of the amateur microscopist, is that a given objective lens can deliver a clear image at a magnification at about 1000 times the numerical aperature.

So a 40X lens with a numerical aperture of .64 could deliver a clear image at 640X. That's why eye pieces ae usually limited to 16X (there are orther reasons as well) A 100X objective lens may have an N.A. of 1.3. Air has a numerical aperture that is slightly less than 1, so for magnificatons of 1000X or more you must not have any air between the subject and the lens, that's why you need a good mountant and an oil immersion lens and you have to use immersion oil to get a good image at 1000X+.

Objective lens
This is the lens that is closest to the object being examined. Changing powers usually means changing the objective lens, most often through use of a rotating turret.

Ocular - see "eye piece"

P.C. Phase Contrast
This technique gives better contrast on unstained specimens and can show as much detail on unstained specimens as on stained specimens and sometimes even more. It gives live protozoans a really "cool" look. Phase contrast can be done with a PC kit or with a dedicated PC microscope. It requires special objectives and a special condensor. A seperate condensor is needed for each power so switching powers requires changing condensors or using special revolving turret condensor. This is considered an advanced and somewhat expensive technique.

Parfocal
This means being in focus on the same setting. The objective lenses of a properly adjusted lab quality micoroscope will be parfocal. A photo tube in a trinocular micoroscope can be adjusted to be parfocal with the eye pieces, but often at only one level of magnification.

Plan
With Most lenses the focus varies across the width of the lens, so if an obeject is in focus when it is centered, it may go out of focus if moved toward the edge. Likewise, a perfectly flat object may be in focus in the center of the field and out of focus toward the edges. A plan objective lens give a flat field across the width of the lens. Plan objecives are considered premium objectives and a set of plan objectives may cost several hundred dollars.

SHC Super High Contrast
This is a type of objective lens that is not as common as standard achromatics or Plan objectives. These objectives give higher contrast images, bringing out more detail, especially on unstained specimens.

Stain
Stains are dyes used to darken or "stain" a specimen to improve conrast and bring out details that might not otherwise be visible. Exessive staining can actually have the opposite effect, hiding details rather than enhancing them, esecially when used with digital cameras.

Stereo Microscope
A microscope with dual objectives and dual eyepieces thus rendering both a right and left eye veiw, allowing objects to be seen STEREOscopically (in "3D"). These are often called "dissecting" microscopes because of their wide use in specimen and slide preparation. They are also used called "inspecton" microscopes and are often used in a variety of other fields such as electronics and medicine, and are even used by mothers to aid in the removal of splinters! Note that though stereo microscopes are usually low power, not all low power microscopes are stereo.

Sub Stage lighting
This the normal lighting method used with high power aka "compound" or "Biolocical" microscopes, in which light from below the stage shines through the subject. This is also known as "light transmission microscopy". This is used in conjunction with various techniques such as Bright Field , Dark Field, cross polarization, Phase contrast, etc.

Super Stage lighting
This is the normal lighting method used with Stereo and other low power microscopes. It is used with opaque objects, and when it is used with opaque objects on a slide the field is dark, similar to when Dark Field is used with translucent objects. With high power microscopes the light comes down at an angle and while it works well at lower powers it is difficult or impossible to use at high powers unless a special microscope is used that has a lighting fixture mounted on the head and special objectives that allow light to shine through special openings, such as a metalurgical or Epi Fluorescence microscope.

Trinocular
This describes a microscope with a speial third optical port which usually points straight up. The third port is used for an optical device, usually a still or video camera. This is often called a "photo tube" and, depending on the configuration, may be used with a film or digital camera, a dedicated microscope camera, or perhaps a video security camera.

W.D. Working Distance
One of the specs of an objective lens, along with power and numerical aperture. The Working Distance describes the distance between the subject and the lens at which the lens is focused. Lower power lenses have a longer working distance, higher power lenses have a shorter working distance. In a lab quality microscope the lenses are designed so that, when the instrument is properly adjusted, all objectives will be in foocus at the same settng of the focus knob. Note, however, that higher power objectives have a more critical focus than lower powers, so slight adjustment of the fine focus know will often be necessary.

W.F. Wide Field
This refers to the viewable part of the eyepice or Ocular, a Wide Field eye peice allows you to back off from the eye piece a bit more and so it is possible to wear eyeglasses while using a microscope. This comes in handy when people with varying degrees of nearsightedness, farsightedness, etc. are alternately looking into the same microscope without using some kind of video or projecton attachment.

W.M. Whole Mount
This term is a little misleading. It means that it is not sliced or sectioned and thus retains the original thickness of the object. A whole mount of a butterfly wing, for example, would not necessarily be an entire butterfly wing, but usually a small piece that is as thick as the orginal rather than a thin slice of it.