FAQ

General

How do I determine the field of view on my microscope?

To calculate the field of view (measured in mm), divide the Field Number on your eyepiece by the magnification number of your objective. For example, a 10X objective used with an eyepiece with a Field Number of 22 gives a 2.2mm diameter field of view. When using a magnification changer, multiply that magnification factor by the objective magnification, and then divide, as before, into the Field Number.

How do I find out about prices or get a quotation?

Pricing is available through your local Olympus direct sales representative or authorized Olympus microscope dealer. To contact your local microscope dealer, click here

Does Olympus have a GSA contract?

Yes. Please call your authorized Olympus dealer for details

What is the adjustment, or parfocalizing, distance of a microscope?

These terms refer to the chosen distance from the opening of the nosepiece to the focused specimen (in most modern microscopes the distance measures 45mm). A standard distance for all objectives makes it easy to rotate a sequence of objectives into the light path while reducing the need to refocus. A set of objectives is considered parfocal if a focused feature remains in focus when objective lens is changed. A set of objectives is considered parcentric if the image remains centered in the field of view as you change objectives.

How do I distinguish the resolving power of an objective from resolution?

Resolving power refers to the clarity with which an objective can clearly separate points or lines lying close together in the specimen. The shorter the distance between points or lines, the greater the resolving power. Also, the higher the NA of the objective, the greater its resolving power.

Resolution refers to the actual separation between points or lines that the microscope achieves.

Sometimes you need to compromise between resolving power and resolution to achieve the best visibility.

How do NA and magnification relate to the brightness of an image?

A higher NA, for a given magnification, yields a brighter image. A higher magnification reduces the brightness of an image.

What is Koehler Illumination?

All Olympus microscopes provide for Koehler Illumination, which uses a filament light source to evenly illuminate a specimen.

Focusing and centering the bulb filament in both the objective back focal plane and the condenser front focal plane maximizes the defocused image of the filament in the image specimen plane, evenly illuminating the entire field of view.

How does a stereo microscope differ from a standard, compound microscope?

A compound microscope has one optical path split at the observation tube to give identical left and right images. A stereo microscope has two optical paths, or axes, offset from one another to mimic the natural offset of two eyes. It is this offset that allows for depth perception in ordinary life and for the three-dimensional view in stereo microscopes.

Objectives

What is numerical aperture, or NA?

Numerical aperture measures the ability of a lens to gather light. The higher the NA, the better the resolution and intensity of the image and the shallower the depth of field. A higher NA objective also usually costs more.

What's the difference between depth of field and depth of focus?

Depth of field describes that region of the specimen, along the optical axis, in sharp focus. As NA increases, depth of field decreases. Depth of focus describes that region in the magnified image in focus at the film plane. As magnification increases, depth of focus decreases.

What is working distance?

Working distance measures the vertical distance in millimeters or microns (not including cover glass space) from the front of an objective lens to the focused specimen.

What are the differences among achromat, fluorite and apochromat objectives?

Achromat, or planachromat, objectives provide correction for 3 wavelengths chromatically and one or two wavelengths spherically in the middle of the visible spectrum. They give their best images in green light, and in white light will yield satisfactory (but not the best obtainable) images for color photomicrography.

Fluorite, or planfluorite, objectives provide correction for four wavelengths chromatically and spherically over a correspondingly wider spectrum than achromat objectives serve. Fluorite objectives yield good and relatively economical images for color photomicrography.

Apochromat, or planapochromat, objectives, for their respective magnifications, have a higher NA than objectives of lesser correction and deliver the highest degree of correction for four wavelengths chromatically and spherically. These are the best objectives for critical resolution and color photomicrography, and they usually have shallower depth of field than the other objectives. They are also more expensive than other objectives.

Why do some objectives have correction caps?

Correction caps, available for "C" series achromat and fluorite objectives, correct for spherical aberrations introduced by glass and plastic. Objectives with correction caps can thus focus through a petri dish or a thick slide without image deterioration.

Why do some objectives require immersion oil or water?

The resolving power of an objective lens depends largely on its numerical aperture (its NA), which in turn depends on the refractive index of the medium between the specimen and the lens. A higher refractive index means the lens can gather more light and deliver images of better resolution and intensity. When air, with a relatively low refractive index, is the medium between specimen and lens, lower NA objectives perform to their capabilities. Higher NA objectives, however, need a higher refractive index to fulfill their capabilities, and oil provides that higher index.
Immersion objectives carry the inscription oil. Some objectives, particularly those used in the observation of living biological specimens, require water as the immersion contact medium. These objectives carry the inscription "WI."

Why do some objectives have an iris?

In order to preserve the darkness of the background during darkfield microscopy, the objective cannot have an NA higher than the lowest NA inscribed on the darkfield condenser. An iris that can reduce an objective's NA, allows you to use high NA objectives for darkfield work. Objectives with an NA above 1.2 absolutely require an iris for darkfield. For ordinary brightfield observation, the iris can simply stay open.

Do I need special objectives for darkfield microscopy?

For reflected light darkfield observation, you need brightfield/darkfield objectives to do darkfield work. These objectives (labeled BD or BF/DF) function with the illuminator optics to keep the illuminating light separate from the image light of the specimen.

In most cases, for transmitted light observation, you will only need a darkfield stop in the condenser. At higher magnifications, however, you will need an objective with an iris as well as a special darkfield condenser.

What does the inscription "0.17" on the objective mean?

The "0.17" refers to the thickness, in millimeters, of the cover glass that was assumed by the lens designer in computing the corrections for the objective. For objectives with a numerical aperture higher than 0.45, a departure in this assumed thickness (or no cover glass at all) may result in deterioration of the image.

What does the objective inscription "160" mean?

This identifies a finite tube-length objective, with a distance of 160mm from the nosepiece (where the objective screws in) to the top of the observation tube (where the eyepiece inserts). If you lengthen this distance by inserting accessories in the light path above the nosepiece, spherical aberration will result unless the accessories include optical correction lenses.

What is an infinity-corrected objective?

With an infinity-corrected objective, light rays emerge in parallel bundles projected toward infinity. Such an objective, which provides many benefits, requires a tube lens in the light path to converge the parallel rays so that they come to focus at the plane of the eyepiece diaphragm.

Why do some objectives have the inscription "Plan"?

A plan objective projects a flat image in the entire field of view. Many objectives will give a flat image with eyepieces of up to Field Number 22. The new planapochromats and planfluorites will give a flat image even with eyepieces of up to Field Number 26.5.

What do the inscriptions "LWD" or "ULWD" mean on an objective?

These letters identify long or ultra-long working distance objectives where the working distance from the front of the objective to the focused specimen is much longer than it is on standard objectives of similar magnification. Long and ultra-long working distance objectives become invaluable when you want to: look up through a culture vessel or petri dish in inverted biological microscopy, look at a thick metallurgical mount in upright incident light microscopy, examine IC wafers to prevent incident contact, or inspect solder connections of mounted chips.

Some objectives carry the inscriptions "NIC" or "DIC." Why?

These letters designate an objective designed especially for use in Nomarski or differential interference microscopy.

Why might I need UV objectives?

UV objectives contain glass elements and coatings designed to transmit the low wavelengths of near ultraviolet light that ordinary glass will not transmit. These objectives come in handy for near ultraviolet excitation in reflected light fluorescence work. The new Olympus infinity-corrected U-planapochromats and U-planfluorites provide this improved transmission in the near ultraviolet.

Why do some objectives of 20X or higher have a spring-loaded or retractable front lens assembly?

These objectives usually have a very short free working distance-which means the front of the objective can inadvertently crash into the cover glass or specimen. A spring-loaded front lens assembly will retract upon gentle contact with the specimen. Such an assembly will not, however, protect against rough and continuous contact.

What is the maximum NA a "dry" objective (an objective requiring air between front lens and specimen) can have?

A dry objective can have an NA as high as 0.95, but to look through a cover glass it will need a correction collar.

Can I use an infinity-corrected objective from another microscope manufacturer on an Olympus infinity-corrected system?

We don't advise it. The Olympus tube lens has a different focal length than that of other manufacturers, so you would get inaccurate magnification. You would also get aberrations because other companies correct for lateral chromatic aberration in the tube lens, and Olympus, in the new B-Max series, achieves this correction in the objectives themselves. Finally, another company's objective probably won't be parfocal with Olympus objectives.

Can I use a planachromat objective in reflected light fluorescence?

Planachromats may serve satisfactorily for blue or green excitation wavelengths, but the planachromat's glass elements may themselves fluoresce in excitation in the near ultraviolet. Also, planachromats, for their respective magnifications, have a lower NA than do planfluorites or planapochromats, so you could get a dimmer image.

Why might I get a worse image with a 50X than with a 20X objective?

The specimen may have a thicker cover glass than the standard 0.17mm, or it may have a thick mounting medium under the cover glass. To improve the image, you might use a dry objective with a correction collar, or you could substitute a 50X oil immersion objective for the 50X dry lens, since the immersion objective has less sensitivity to variations in cover glass thickness.

How can I minimize the likelihood of getting immersion oil on the 50X dry objective?

To reduce the chance of inadvertently dipping the 50X dry objective into immersion oil as you rotate the nosepiece between that objective and the 100X oil immersion objective, laboratories often mount the two objectives on opposite sides of the nosepiece from one another.

How can I avoid the oiling hazard with the 50X dry objective?

If you use the100X oil immersion objective frequently, you might want to substitute a 50X oil immersion objective for the 50 X dry objective. The 50X (NA 0.90) oil planachromat will yield much brighter images, with better resolution, than the standard 50X (NA 0.80) dry planachromat or achromat

Should I buy the highest correction objectives I can afford?

Usually, but not always. If you mostly want to observe specimens thicker than several microns, planachromats or planfluorites may serve quite well because they have greater depth of field than planapochromats of comparable magnification. For color photomicrography, planfluorites render better images than planachromats. Planapochromats deliver the finest color photomicrography, as well as the finest observation, of minute details, but planapochromats also cost several times what planfluorites cost.

Should I choose the highest available NA objectives for video microscopy of minute specimen details?

Yes. While glare may appear to obscure details of the image when you look through the eyepiece, the necessary information is probably there, and video enhancement techniques can process the information and render an excellent video image.

Components

What does "C" or "K" or "WF" or "H" mean when inscribed on the eyepiece?

Some microscope objectives do not include correction for lateral chromatic aberration and require a compensating eyepiece (labeled "C" or "K") to provide this correction.
"WF" signifies "widefield," meaning you can see more of the specimen at a given time. "H" signifies "high eyepoint," which means you don't have to put your eyes very close to the eyepiece during observation-a great advantage if you wear glasses.

Why do some observation tubes have notches cut into them?

The notch guides placement of the locator pin on eyepieces that have a reticle. You focus such an eyepiece by rotating the diopter adjusted upper lens, while the locator pin keeps the reticle crosshairs or micrometer scale properly oriented.

What is the external diameter of the most common observation tubes?

They're usually 25mm-but 30mm on the latest Olympus B-max microscopes and all Olympus super-wide observation tubes.

What is a photo-eyepiece?

Used for photomicrography rather than observation, a photo-eyepiece picks up the image delivered by the objective and projects it onto the film plane inside the camera. Photo-eyepieces usually come with low magnification power to lessen the chance of empty magnification when the images they project onto film are subsequently enlarged.

With an objective of a given magnification, why can't I use eyepieces of increasingly higher magnification to achieve higher total magnification?

To maintain useful magnification yielding satisfactory clarity and resolution, you must avoid empty magnification or making the specimen appear larger but not clearer. As a general rule, total magnification should not exceed 750X-1000X the NA of the objective. For example, with a 40X, NA 0.65 objective, the total magnification (the multiple of eyepiece and objective magnifications) should lie between 480X and 650X.

How does a sub-stage condenser function?

You determine the working NA of a microscope by adding the NA of the objective to the NA of the condenser and then dividing by 2. In order to retain the best balance of contrast and resolution, you want to keep the iris aperture diaphragm of the condenser open to about 3/4 of the NA of the objective. Condensers vary in their color and spherical correction-from the modest correction of an Abbe condenser to the highest correction aplanat-achromat condenser (which, with its high NA, is the best choice for color photomicrography). Some condensers have an upper element that can swing out of the light path, allowing the condenser to fill, without vignetting, the field of view of a 4X or 2X objective.

Filters

What does a neutral density filter do?

Very useful in photomicrography and video microscopy, the neutral density filter absorbs light evenly throughout the visible spectrum, thus lowering the intensity of light without changing its color.

What is a daylight blue filter, and do I need one?

A "daylight blue" filter absorbs some of the yellow to red light from the microscope lamp, resulting in a coloration much closer to daylight, benefiting more comfortable viewing.

Many users also prefer the daylight color temperature the filter provides for comfortable viewing. This option is unnecessary with new LED lighting.

How is the daylight blue filter used and misused?

Intended only for observation purposes, the daylight blue filter provides a pleasant background to the field of view. Do not use this filter for photomicrography with daylight color film. Such film requires a blue "conversion filter" (such as the Olympus LBD or Kodak 80A) to boost the color temperature of the light source to the film's requirements.

Why place a green filter in the light path?

Green light delivers the best spherical correction for achromats and planachromats. And, since monochromatic light eliminates chromatic aberration, a green filter markedly improves the performance of achromats. Also, phase contrast objectives give their best images in green light.