What is
the difference between a stereo microscope and a compound
microscope?
A compound microscope has one optical path that is split at
the observation tube that gives identical left and right
images. A stereo microscope is like two compound microscopes
side-by-side but with an offset from one another to mimic
the natural offset of two eyes. It is the offset that
provides depth perception in ordinary life and for the
three-dimensional view or “erect image” in stereo
microscopes.
What is the
difference between resolving power of an objective and
resolution?
Resolving power refers to the clarity with which an
objective can clearly separate two points or lines lying
close together. The shorter the distance between the points
or lines, the greater the resolving power. Also the higher
the N.A. (numerical aperture) number of the objective, the
greater it’s resolving power. Resolution is the ability to
distinguish two points as two points. One may need to
compromise between resolving power and resolution to achieve
the desired image.
How
do N.A. and magnification relate to the brightness of an
image?
The higher the N.A. value, for a given magnification, the
brighter the image. A higher magnification reduces the
brightness of an image.
What is “Depth of field”?
The height difference within features of an object that
appear acceptably sharp when viewed with an optical
instrument. Depth of field depends on the objectives,
eyepieces and tube factor. Depth of field decreases when
increasing magnification.
What is Dioptric correction or adjustment?
Dioptric correction is the compensation of long- or
short-sightedness by the adjustment of the eyepieces.
What is meant by eyepoint?
Light rays from all points in the field of view converge
together at this point. This is where the user’s eye must be
positioned
Explain what “Field Number” means.
The field number is the diameter of the eyepiece lens
usually expressed in millimeters.
What is “Field of view”?
Field of View, or FOV, is the amount of the object that can
be seen with a particular optics combination. It is the
circular area which can be seen when looking into a
microscope. It is a combination of objective and eyepiece
characteristics and field of view decreases with increasing
magnification. In most cases, the field number of the
eyepiece can be used to determine the FOV or field size
using the following formula:
Field Size = Field Number ÷ Objective Magnification
What is
Interpupillary Distance?
Interpupillary Distance is the distance between the centers
of the pupils of your two eyes.
What is meant by parfocal?
A stereo microscope can be said to be “parfocal” when an
object can be observed from the lowest magnification to the
highest without having to re-focus.
What does working distance mean?
The working distance is the distance from the object plane
to the front of the objective.
Working distance decreases each time a higher-power
objective is used.
How is Total Magnification calculated?
The total magnification a microscope configuration is
calculated from the magnifying power of the objective
multiplied by the magnification of the eyepiece and, if
installed, multiplied by the auxiliary lens.
What
is meant by the term “Useful Magnification”?
Useful magnification is obtained when the magnification is
between 500 and 1000 times the numerical aperture of the
objective. Since the human eye has limited resolving power,
the magnification should be selected so that the image
details can still be distinguished by the eye. If the
magnification falls below this range, details can no longer
be recognized by the eye. If the magnification is above this
range, this is simply referred to as “empty magnification”
as the objective is no longer able to resolve structures.
The image therefore appears out of focus.
Why
do some objectives require immersion oil or water?
The resolving power of an objective lens depends on its
numerical aperture, which in turn depends on the refractive
index of the medium between the specimen and the objective
lens. A higher refractive index means the lens can gather
more light and deliver a better image intensity. Air has a
relatively low refractive index, and when it is the medium
between specimen and the lens, lower N.A. objectives perform
at their best capacity. Higher N.A. objectives need a higher
refractive index to operate and immersion oil provides that
higher index. For optimum performance, you will also need to
oil the top lens of the condenser to the bottom of the
specimen slide. Immersion objectives are marked "oil" or
"oel". Objectives marked "wi", require water as the
immersion contact medium.
Why do some
objectives have an iris?
In order to preserve darkness of the background for
darkfield microscopy, the objective cannot have an N.A.
higher than the lowest N.A. marked on the darkfield
condenser. An iris that can reduce an objective's N.A., can
allow you to use higher N.A. objectives for darkfield work.
Objectives with an N.A. above 1.2 require an iris for
darkfield. For ordinary brightfield observation, the iris
can simply stay wide open.
Do I
need special objectives for darkfield microscopy?
In most cases, from a transmitted light observation, you
will only need a darkfield stop in the condenser. At higher
magnifications, you will need an objective with an iris as
well as a 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, departing from
this thickness (or using no cover glass at all) may result
in a less than satisfactory image.
What does
the objective inscription "160" mean?
The 160 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). When you lengthen this distance by
inserting accessories in the light path above the nosepiece,
spherical aberrations will occur unless the accessories
include the proper optical corrections.
What is an
infinity-corrected objective?
With an infinity-corrected objective, light rays emerge in
parallel projected toward infinity. Such an objective
requires a tube lens in the light path to converge the
parallel rays so that they come into focus at the eyepiece
diaphragm.
Why
do some objectives have the inscription "Plan?"
A plan objective projects a flat image of the entire field
of view.
Why do objectives usually have a color ring on them?
With standard colors for most manufacturers, these rings
make it easy to identify the magnification of the objective:
A red
ring means 4X or 5X. A yellow ring means 10X. A green ring means 20X. A blue ring means 40X, 50X or 60X. A white ring means 100X.
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 is much longer than
standard objectives of similar magnification.
What
do objectives with the inscriptions "NIC" or "DIC" mean?
These letters designate an objective designed especially for
use in Nomarski or differential interference
microscopy. Meiji does not currently offer either
method.
Why
do some objectives have a spring-loaded front lens?
These objectives will have a very short working distance. To
protect your microscope objective and your specimen, a
spring-loaded front lens assembly retracts upon gentle
contact with the stage or specimen. The retractable lens
will not, however, protect against rough and continuous
contact also known as “crashing” the objective.
Why
am I getting a worse image with a 40X than with a 20X
objective?
The specimen may have a thicker cover glass than the
standard 0.17mm, or you may have a thicker than normal glass
slide. To improve the image, you might try using a dry
objective with a correction collar, or you can try using 40X or 50X
"oil immersion" objectives, since the immersion objective has
less sensitivity to variations in cover glass thickness.
Can I
use phase contrast objectives for other types of
observation?
Yes. Just move the phase condenser to the brightfield or
“empty” position and employ the standard Koehler
illumination procedure.
Can I
use an infinity-corrected objective on a finite tube length
microscope?
No, because the finite system does not include a tube lens
to focus parallel rays.
What
does "C" or "K" or "WF" or "H" mean when printed on the
eyepieces?
Microscope objectives do not include correction for lateral
chromatic aberration and require a compensating eyepiece
(labeled "C" or "K") to provide 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 so close to the eyepiece during
observation. These are typically meant for users who wear
eyeglasses but anyone can use them.
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 magnified.
Why
can't I use eyepieces of increasingly higher magnification
to achieve higher total magnification?
To maintain useful magnification with satisfactory clarity
and resolution, you must avoid empty magnification or making
the specimen appear bigger but not clearer. In general,
total magnification should not exceed 750X-1000X the N.A. of
the objective. For example, with a 40X, N.A. 0.65 objective,
the total magnification should be between 480X and 650X.
What
does a neutral density filter do?
Neutral density filters absorb light evenly across the
visible spectrum, thus lowering the intensity of light
without changing its color temperature.
What
is a daylight blue filter, and why do I need one?
A "daylight blue" filter absorbs some of the yellow to red
light from the microscope lamp, resulting in coloration much
closer to natural daylight which is beneficial comfortable
viewing.
How
is a daylight blue filter used?
Use of a daylight blue filter is intended for observation
purposes only, providing a pleasant background to the field
of view. Do not use this filter for photomicrography or with
daylight color film.
Why
place a green filter in the light path?
Human eyes see the color green the best. And, since
monochromatic light eliminates chromatic aberration, a green
filter markedly improves the performance of achromats. In
addition, phase contrast objectives give their best images
with green light.
What is the difference between
achromat & plan achromat objectives?
Objectives are corrected for field curvature and color
aberration. The difference between Achromats and Plan
Achromats is the degree of the flatness of field. When the
image is in focus from the center towards its edges; the
field is said to be "flat". In general, the flatter the
field of an objective, the more lenses it contains and the
more expensive the cost.
What does "DIN" standard mean?
"DIN" is an abbreviation of "Deutsche Industrial Normen."
This is a German standard that has been adopted
internationally as an optical standard used in most quality
microscopes. The focal tube length of a DIN objective is
160mm. The former standard was RMS ("Royal Microscope
Society"), which had a longer tube length (170mm). Most DIN
optics can be interchangeable. However, DIN and RMS
objectives are not interchangeable.
What does "FN" stand for?
A number usually engraved on an eyepiece, which refers to
the diameter of a baffle or raised ring inside the
eyepiece. The "FN" of “field number” determines the viewing
field for the eyepiece.
What kind of illumination options do you have?
Proper
illumination is critical to obtain a good image through any
microscope so this topic deserves some time to research.
Meiji Techno offers several options from which to choose.
Whatever your specimen may be, Meiji has the
appropriate
illumination source to help to produce the best image
possible.
What is the difference in types of illumination?
Incandescent - Standard bulb filament,
usually 6 -120V, 20 - 60W. Color temperature is "warm" and
tends to look yellow.
Halogen
- Usually low voltage, cooler, more intense illumination.
Temperature is ideal for color photography.
Fluorescent
- A "cool" system which produces more light and has longer
bulb life than incandescent bulbs. Fluorescent illumination
offers a more desirable color temperature (4100º Kelvin)
with a "whiter" field of view and is more comfortable to the
eyes.
What does coaxial mean?
Coaxial refers to the movement of coincident axes or gears
that share one common axis. On the coaxial controls of a
graduated mechanical stage, one knob controls the "X axis"
movement and the other controls the "Y axis" movement. On a
coaxial focusing system the fine focus control is inside of
the coarse focus control.
What is darkfield microscopy?
Darkfield Microscopy is a method by which the specimen
(transparent or semi-transparent) is seen as a bright object
against a dark, usually black, background.
What is brightfield microscopy?
Brightfield
is perhaps the most common type of microscopy
found in schools, industry and medical fields. In
brightfield microscopy, a transparent or translucent
specimen either naturally colored or stained appears dark
against a bright background or field.
What is phase contrast?
A technique for revealing the structural features of
microscopic transparent objects that cannot otherwise be
accomplished with brightfield microscopy. Phase appears to
achieve the same effect as staining a specimen (which would
kill a live specimen).
What is oil immersion?
Oil immersion is used with high power objective lens
(usually 100X) as a medium between the lens and the cover
slip. Because oil has the same light transmitting properties
as glass, it cuts down the refraction of light rays. Other
requirements include the use of a 1.25 Abbe condenser to be
used.
Can I add a mechanical stage to my microscope?
A mechanical stage can be added to most Meiji Microscope
models.
Can I attach a video camera to my microscope?
Yes. Video cameras, as long as they are the common "C-mount"
type, can be used with most Meiji Microscope models.
Can I add a 35mm camera to my microscope?
Yes, with a universal adapter and “T-Mount” matched to your
camera brand and model.
Can I attach a digital camera to my microscope?
We do not carry digital cameras at this time. We do however
manufacture digital camera adapters for many commercially
available camera makers which can be found online
HERE.
Can I clean my microscope myself?
Blurred images are usually the result of a dirty, scratched
or broken objective. "Black spots" are dirt particles in the
eyepiece or dirt particles on head prism or mirrors. The
following method works on them all:
The front lens of the objectives (particularly the 40X)
should be cleaned after use by first brushing with a soft
camel-hair brush to remove particles of dust, then by wiping
gently with soft lens tissue, moistened with Xylene or clean
distilled water and drying with clean lens paper immediately
following. The objective should never be taken apart except
by a qualified repair person. If dust is seen on the back
lens of the objective, an all-rubber ear syringe or enema
tube may be utilized to blow the dust out.
The eyepiece may be cleaned in the same manner as the
objectives, except in most cases Xylene will not be
required. In most instances breathing on the lens to
moisten it, then wiping dry with clean lens tissue will be
sufficient to clean the surface.
The finish of Meiji microscopes is hard epoxy and is resistant
to acids and reagents. Clean this surface with a damp cloth
and mild detergent.
Note:
Use alcohol for difficult cleaning and as a last resort
Xylene or Acetone. Be forewarned that use of these chemical
cleaners will destroy lens coatings!
If the problem requires more than a simple cleaning, your
Meiji Techno Representative can refer you to an experienced
microscope service dealer in your area.
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