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Compound microscope basics

The greatest confusion is between binocular compound and binocular stereo microscopes. The first uses two eyepices, but they converge into a single optical path using prisms in the eyepiece head. A binocular stereo system retains seperate optical paths all the way to the subject, or final objective (depending on type). This will hopefully help in explaining why a stereo microscope gives that 3D perception, because in effect each eye is veiwing the subject from two slightly different angles.

The compound views only vertcally from above the sample. The compound / upright / routine light microscope, can have one or two eyepieces, monocular and binocular, when a tinocular head is stated this means it has a third optical port, which allows a camera to be fitted, without first removing an eyepiece. A stereo microscope can never have less than two eyepieces!! The term compound comes from the way the optical system works. Magnification is achived using at least two lenses. For example if you have 10x eyepieces and a 10x final objective lens, the magnication will be 100x, this is compound magnification.

The following list explains the main parts of your compound microscope and the function of each:Condenser: The light rays from the illuminator are condensed and focused through this lens in the center of the stage, providing better image resolution. Our 1000x models have a built-in, movable 1.25 Abbe condenser underneath the stage.Disc Diaphragm or Iris Diaphragm: The disc diaphragm is used on most microscopes without 1000x. It's a rotating disc fixed under the stage, designed to provide optimum resolution for the objective lens. Turn the disc to the smaller holes for low magnification (40x and 100x) and to the larger holes for high magnification (400x). Most 1000x models have a fully-adjustable iris diaphragm with an easy, sliding control lever rather than a rotating disc. This type of diaphragm provides greater control of contrast and helps achieve high image resolution.Eyepiece: The part of the microscope that you look through. Eyepieces in most compound microscopes have a lens with a 10x magnification level. Our Advanced microscope has a pointer built in, which appears as a black line across half of the field of view. To move the pointer, just turn the top of the eyepiece.Field of view: This is the area visible when you look through the eyepiece. The greater the power used, the smaller the field of view (i.e., FOV at 40x is much greater than at 1000x. This is why you should locate a specimen at lowest power and then gradually narrow your focus as you are increasing magnification).Filter holder and filters: Some microscopes (like our Home 1000x) come with a swing-out filter holder at the bottom of the condenser. Blue and yellow filters can be used to enhance the image in some situations.Focusing: This moves the microscope stage up and down to bring the slide sharply into view. Most of our microscopes have both fine and coarse focusing, either as two separate knobs or else coaxial (for easy reach).Head: The standard head type is monocular - just one eyepiece. Some microscopes will have a dual head for simultaneous teacher and student viewing of a slide or for video/digital photography. The most deluxe models have binocular heads for extra-comfortable viewing.Illumination: Tungsten is the least expensive illumination. Although it tends to be hotter and less bright than the other kinds. Fluorescent illumination provides cooler and brighter light than tungsten. This is beneficial when viewing slides for long periods of time or observing live specimens, such as protozoa. Halogen provides the very brightest illumination. Our best microscopes have halogen lighting and our stereo microscopes with top lighting also use halogen lighting.Lenses: Standard achromatic lenses help prevent color distortion. Semi-plan or plan lenses improve image quality through superior clarity and flatness. Super High Contrast lenses offer extra image contrast so that the image appears much sharper.Magnification: Multiply the magnification of the eyepiece by the magnification the objective lens for the total magnification at that power. 400x or 1000x is necessary for studying cells and cell structure.Mechanical stage: This fits onto the stage (in some microscopes it is built-in) and provides the best slide control, making viewing easier. Clip the slide into place and use the X and Y-axis knobs to move the slide back and forth under the objective lens.Objective: The second lens of the microscope. Compound microscopes have a "nosepiece" with a rotating objective turret, which allows you to change the magnification level for different specimens. The standard objectives are 4x, 10x, and 40x for total magnification of 40x, 100x, and 400x. DIN is an international standard of lens quality. Oil-immersionObjective: Some microscopes have a fourth objective, a 100x oil-immersion lens for 1000x magnification. This allows you to see greater cell detail and cell structure. To use this lens, you need to put 1-2 drops of immersion oil on the slide coverslip. Immersion oil prevents light distortion, so that you can see a sharp image.Parcentered: This term means that if you centered your slide while using one objective, it should still be centered even when you switch to another objective.Parfocal: This term means that once you have focused on an object using one objective, the microscope will still be coarsely focused when you switch to a different objectiveStage: The platform that holds the slide up beneath the objective lens. The stage clips hold the slide in place. (In some microscopes, these are replaced by a mechanical stage).Stage stop: This is the small bar and screw between the stage and the arm of the microscope. It prevents the stage from coming too far up, so that the stage can't grind against the objective lens. This is also known as a "safety rack stop," and is pre-adjusted by the manufacturer.

Generally speaking, in conclution, if you require magnifaction above 100x and your sample is either fairly flat, or you have prepared it and light can pass through it (unless you have incident EPI illumination), then a compound optical system may be the way to go. Most optical measuring systems also use a single optical path, in order to remove parrallax. When viewing down deep holes, a single vertical optical path is also usually better. However if you require magnifcation under 100x, require depth of focus, field of view and 3D perception, wish to manipulate, dissect or re work it - use a stereo. If in doubt, call us for a chat!


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