Eye piece of a microscope/cosmetic dentistry courses

INDIAN DENTAL
ACADEMY
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♣ MICROSCOPE Basics and Beyond
by
Mortimer Abramowitz Fellow, New York
Microscopical Society For Olympus
America Inc.
Vol. I
♣ OPTICAL MICROSCOPY
by
Michael W. Davidson
(National High Magnetic Field Laboratory,
The
Florida State University)
and
Mortimer Abramowitz
(Olympus America, Inc.,2 Corporate Centre
Dr., Melville, New York-11747,)
♣ Theory and Practice of Histological
techniques – John D Bancroft & Marilyn

At the end of the seminar the learner should be able to understand
•Eye piece
•Components of eye piece
•Types of eye piece
•Terms related to eye piece

Eye piece:
øAlso known as ocular lens.
øIt is a type of lens that is attached to a each and every variety
of optical devices such as telescopes and microscopes.
øIt is so named because it is the lens closest to the eye.
øThe objective lens collects light and brings it to focus
creating an image.

ø The eyepiece is placed near the focal point of the
objective to magnify this image.
øThe amount of magnification depends on the focal
length of the eyepiece.
ø The compound microscope achieves a two-stage
magnification.
ø The objective projects a magnified image into the
body tube of the microscope and the eyepiece further
magnifies the image projected by the objective

ø For example,
the total visual magnification using a 10X objective
and a 15X eyepiece is 150X.

Components of Eye piece

øUW, which is an abbreviation for the Ultra Wide viewfield.
øH designation, to indicate a high-eyepoint focal point,
that allows microscopists to wear glasses while viewing
samples.
øWF for Wide-Field;
øUWF for Ultra Wide-Field;
øSW and SWF for Super Wide-Field;
Inscriptions on Eye piece

øCF for eyepieces intended for use with CF (chrome free )
corrected objectives .
øCompensating eyepieces are often inscribed with K, C,
or Comp ,as well as the magnification.
ø Eyepieces used with flat-field objectives are sometimes
labeled Plan-Comp.

ø The eyepiece magnification of the
eyepieces =10x (indicated on the
housing),
And
ø A/24 indicates the field number is
24,(in mm)
which refers to the diameter
apperture of the fixed diaphragm in
the eyepiece.

ø These eyepieces also have a focus adjustment and a
thumbscrew that allows their position to be fixed.
ø Manufactures now often produce eyepieces having
rubber eye-cups that serve both
ø to position the eyes the proper distance from the
front lens,
øand
ø to block room light from reflecting off the lens
surface and interfering with the view.

Types on Eye piece
ø There are two major types of eyepieces that are grouped
according to lens and diaphragm arrangement.
øThe Negative eyepieces with an internal diaphragm
And
øThe Positive eyepieces that have a diaphragm below
the lenses of the eyepiece.

ø Negative eye piece
øNegative eyepieces have two lenses:
øthe upper lens, which is closest to the observer's eye,
is also called the eye-lens
and
øthe lower lens (beneath the diaphragm) is often termed
the field lens.

In its simplest form
Negative eye piece
also known as
Huygenian eye
piece

ø In their simplest form of this type of eye pieces, both
lenses are plano-convex, with convex sides "facing“
the specimen.
ø Approximately mid-way between these lenses there
is a fixed circular opening or internal diaphragm
which, by its size, defines the circular field of view
that is observed in looking into the microscope.

ø It is found in most of the teaching microscopes
øAlthough the Huygenian eye and field lenses are
not well corrected, their aberrations tend to
cancel each other out.
øMore highly corrected negative eyepieces have
two or three lens elements cemented and
combined together to make the eye lens.

ø If an unknown eyepiece carries only the
magnification inscribed on the housing, it is most
likely to be a Huygenian eyepiece,
ø Best suited for use with achromatic objectives of
5x-40x magnification.

øPositive eye piece
ø The other main kind of eyepiece is the positive
eyepiece with a diaphragm below its lenses,
øcommonly known as the Ramsden eyepiece

ø This eyepiece has an eye lens and field lens that are
also plano-convex.
ø But the field lens is mounted with the curved surface
facing towards the eye lens.

ø The front focal plane of this eyepiece lies just below
the field lens.
ø i.e at the level of the eyepiece
diaphragm.
øAnd thus making this eyepiece
readily adaptable for mounting
reticles.
øTo provide better correction, the two lenses of the
Ramsden eyepiece may be cemented together

øKellner eyepiece
ø A modified version of the Ramsden eyepiece is
known as the Kellner eyepiece
øThese are the improved eyepieces contains
ø A doublet of eye-lens elements cemented
together
and
øFeature a higher eyepoint more than either the
Ramsden or Huygenian eyepiece (eyepieces in
their simplest form)
ø A much larger field of view.www.indiandentalacademy.com

øCompensating eyepieces
ø Simple eyepieces (Huygenian and Ramsden) will not
correct for residual chromatic difference of
magnification in the intermediate image. (formed by
the objective)
øTo remedy this, manufacturers produce compensating
eyepieces that introduce an equal, but opposite,
chromatic error in the lens elements.
ø It may be either of the positive or negative type.
ø And used at all magnifications with fluorite,
apochromatic and all variations of plan objectives

øCompensating eyepieces play a crucial role in helping to
eliminate residual chromatic aberrations inherent in the design
of highly corrected objectives.
øHence, it is preferable that the microscopist uses the
compensating eyepieces designed by a particular
manufacturer to accompany that manufacturer's higher-
corrected objectives.

ø In recent years, modern microscope objectives have their
correction for chromatic difference of magnification either
ø Built into the objectives themselves
(Olympus and Nikon)
or
ø Corrected in the tube lens
(Leica andZeiss).

ø Periplan eyepieces
øMost advanced eyepiece
øThis eyepiece contains seven lens elements that are
cemented into a
ø Single doublet,
ø A single triplet,
and
ø Two individual lenses

Advantage:
øBetter correction for residual
Lateral chromatic aberration,
øIncreased flatness of field,
And
ø A general overall better
Performance when used with
Higher power objectives
Disadvantage:
øProduces internal reflection
(minimized by internal silver coating)

ø In addition, most microscopes now feature much
wider body tubes that have greatly increased the
size of intermediate images
ø To address these new features, manufacturers
now produce wide-eyefield eyepieces that increase
the viewable area of the specimen by as much as 40
percent.

øHow to select the best one...??
ø When choosing eyepieces, it is relatively easy to differentiate
between simple and more highly compensated eyepieces..
ø When
viewed through the microscope
Or
held up to a light source
øRamsden and Huygenian (and their more highly corrected
counterparts) will appear to have a blue ring around the
edge of the eyepiece diaphragm.
øIn contrast, more highly corrected compensating eyepieces
with have a yellow-red-orange ring around the diaphragm
under the same circumstances.

øProperties of an eyepiece
EYEPIECE TYPE FINDER EYEPIECES
SUPER
WIDEFIELD
EYEPIECE
WIDE FIELD EYEPIECES
DESCRIPTIVE
ABBREVIATION
SWH
10x
WH
10x
SWH
10x
SWH
10x H
WH
10x H
WH
15x H
WH
10x H
FIELD NUMBER 26.5 22 26.5 26.5 22 14 22
The properties of several common commercially available
eyepieces (manufactured by Olympus America, Inc.) are listed
according to type in given table

øHigh eye point eye piece :
øLight rays radiate from the eyepiece intersect at the exit
pupil or eyepoint , often referred to as the Ramsden
disc
øPoint where the pupil of the microscopists eye should be
placed in order to see the entire field of view
(8-10 mm from the eye lens)
ø By increasing the magnification of the eyepiece, the
eyepoint is drawn closer to the upper surface of the eye
lens.
ø Which making it much more difficult for the microscopist
to use, especially if they are wearing eyeglasses.

ø To compensate for this, specially designed high
eyepoint eyepieces have been manufactured
ø Eyepoint distances approaching 20-25 mm above the
surface of the eye lens.
øThese improved eyepieces have
ø larger diameter eye lenses
ø With more optical elements
øFeatures of improved flatness of field
øHave inscription "H" somewhere on the eyepiece housing

1 Real image ; 2 - Field diaphragm ; 3 - Eye relief ; 4 - Exit pupil/ Ramsden fisc

øView field diameter of eye piece :
ø The diameter of the viewfield in an eyepiece is expressed as a
"field-of-view number"
Or
Field number (FN
øField number of an eyepiece can give us the real diameter of
the object viewfield using the formula:
øViewfield Diameter = (FN) / (M(O) × M(T))
øwhere FN is the field number in millimeters,
øM(O) is the objective magnification,
øM(T) is the tube lens magnification factor (if any)

Magnification Viewfield Diameter (mm)
1/2x 42.4
1x 21.2
2x 10.6
4x 5.3
10x 2.12
20x 1.06
40x 0.53
50x 0.42
60x 0.35
100x 0.21
150x 0.14
250x 0.085

øReticles of eye piece :
ø Eyepieces can be adapted for measurement
purposes by adding a small circular disk-shaped
glass reticle.
øAt the plane of the field diaphragm of the eyepiece.
øReticles usually have markings, such as a measuring
rule or grid, etched onto the surface.
øBecause the reticle lies in the same plane as the field
diaphragm, it appears in sharp focus superimposed
over the image of the specimen.

øReticles of eye piece :
ø Eyepieces using reticles must contain a focusing
mechanism (usually a helical screw or slider)
øThat allows the image of the reticle to be brought
into focus.
øSeveral typical reticles are...

Rectangular
micrometer
Used in
Photomicrography
Linear
micrometer
measure image
distances
Crossed
micrometer
is used with
polarizing
microscopes.
To locate the
alignment of
samples with
respect to
the polarizer
and analyzer
Used to
partition a
section of the
viewfield for
counting.

øFilar Micrometer :
ø For highly accurate measurements
øThis micrometer replaces the conventional
eyepiece and contains several improvements over
conventional reticles.
ø In the filar micrometer, a reticle with a measuring
scale and a very fine wire is brought into focus
with the specimen.

øFilar Micrometer :

ø Some eyepieces have a movable "pointer" located within
the eyepiece.
ø used in teaching microscopy.

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