Choosing The Correct Reticle Glass Diameter For Your Eyepiece
microscope eyepieces (oculars) are designed to accept a reticle
on the inside of the bottom of the eyepiece. This is the end of
the eyepiece that normally sets in the microscope's eyetube,
which is the tube that is attached to the microscope.
order for the eyepiece to properly use a reticle it will need
two things. You can check for these by removing the eyepiece
from the eyetube, turning it over and looking down inside the
bottom of the eyepiece. 1) There must be a "shelf"
(a.k.a. field stop) of some kind
down inside the eyepiece for the reticle to rest on, and 2)
there must be a retaining mechanism of some kind to hold the
reticle in place. This shelf is very important as it positions
the reticle at the focal plane of the eyepiece lens.
This means the reticle is spaced correctly to be in focus when
you view it through the top of the eyepiece. The retaining
mechanism is typically a threaded ring that you unscrew from the
inside of the eyepiece. You then set the reticle down inside on
the shelf, and screw the retaining ring back in to hold the
reticle in place. You will probably need a spanner wrench or very small flat screwdriver
to remove and re-install this threaded ring. If there is no retaining
device but there is
a shelf for the reticle, then you can
buy a properly sized C-Ring Retainer
hold the reticle in place. Choose the C-Ring size that matches
the reticle diameter (as determined in the next paragraph).
If there is no shelf for the reticle to rest on in the bottom of
the eyepiece, then either your eyepiece uses a different method
of holding its reticle, or it is not able to accept
one. Some eyepieces are designed so the reticle is installed
in-between two lenses instead of at the bottom, or possibly by
some other method. In this case you would need to refer to the
owner's manual or contact the manufacturer/dealer. Ask them if
the eyepiece can accept a reticle and how to determine the
proper glass diameter.
you have determined your eyepiece has the necessary shelf for
the reticle you would then measure the inside
diameter of the bottom of the eyepiece. Be sure you are
measuring against the inside wall of the eyepiece and not the
inside of any retaining ring that may be in there. This
measurement must be reasonably accurate. It will typically be a
fraction of a millimeter over a whole, integer number. For example it may
measure 19.3 mm. You would then round down to the nearest
millimeter, in this case 19mm, and that would be the proper
diameter for the reticle. Another example is you measured
23.1 mm. You would then select a 23 mm reticle diameter. The
tolerance on the reticle's diameter is +0.000" / -0.005" so as
long as the inside diameter of the eyepiece is slightly larger
than the reticle diameter it should fit.
are a few exceptions to this integer method of selecting a
diameter. For example, Olympus has a few eyepieces designed for
20.4mm diameter reticles, Leica has some for a 24.5mm
diameter, and Accu-Scope has some for a 26.5mm diameter, so we carry those,
plus 1 in. (25.4mm), as standard
products. But the majority of eyepieces are designed to
accept an integer number diameter. Of course we can make custom
diameters upon request.
Please note that a typical eyepiece will have numbers written on
the outside such as WF10X/20MM. These numbers are not
specifying the diameter of a reticle for that eyepiece. They are
specifying the magnification of the eyepiece and its aperture
(optical field diameter). Unless you have the reticle diameter as specified by the
owner's manual or other manufacturer's specification, you must
measure per the instructions above.
Choosing The Correct Reticle Scale Value For Your Objective
If you need to order a reticle for your application, use the
following to determine the correct scale value.
When ordering reticles, take into consideration only your total objective magnification (don't add
in the eyepiece). On a typical zoom stereo microscope it would be between
1X and 5X. If you installed a 1.5X auxiliary objective lens on
that same stereo microscope, it would then be between 1.5X and
7.5X. On a compound microscope it would typically be between
4X and 100X.
Using the 3X objective lens on your stereo microscope, you
want to be able to measure .001" of your target specimen
for each division of your reticle. Therefore, use the following formula:
Formula: Desired value of Target x Objective = Value of Reticle
.001" x 3X = .003" per division
You can see you need a reticle that has
.003" per division.
If you want 100 divisions: .003" x 100 divisions = .300"/100
div. (Part #
If you want 200 divisions:
.003" x 200 divisions = .600"/200 div. (Part #
Below are examples of the different values
attained from this reticle when used with various objective
Part # S-14278
divisions, each division equals .003" actual value.
.003" @ 1x objective setting = .003" at target
.003" @ 2x objecting setting = .0015" at target
.003" @ 3x objective setting = .001 " at target
If you already have a reticle, use the following to determine
its measurement resolution.
You have a S-14314
which has a 10mm scale divided into 100 divisions. Therefore each division is 0.100 mm (100
micron). If you use the 40X objective lens on your compound
microscope, you want to know the corresponding dimension of your
Formula: Reticle Value / Objective = Value at Target Specimen.
0.1mm / 40 = 0.0025mm (2.5 micron or 2.5µ)
Below are examples of different values attained from this reticle
used with various objective settings.
Part # S-14314
: 10mm scale with 100 divisions, each division equals 0.10mm actual
0.10mm / 4x obj. = 0.025 (25µ) at target specimen.
0.10mm / 10x obj. = 0.010 (10µ) at target specimen.
0.10mm / 40x obj. = 0.0025 (2.5µ) at target specimen.
0.10mm / 100x obj. = 0.001 (1µ) at target specimen.
Calibrating Your Reticle With a Stage Micrometer
For precise measurements, each reticle must be calibrated to each objective using a Stage Micrometer.
Procedure for Calibrating Each Objective:
Accurate measurement of microscopic objects requires
the use of an eyepiece reticle (a.k.a. eyepiece micrometer) and a stage
micrometer. The eyepiece reticle is a round glass disk with a
precision scale on its surface. The eyepiece reticle is
inserted into one eyepiece and must be in focus. The
eyepiece and eyepiece reticle can be rotated 360 degrees in
the eyetube so the measuring scale can be aligned with or
superimposed over the image of your specimen. A typical eyepiece
reticle would be a 5mm or 10mm linear scale featuring 50 or
100 divisions. Before using the eyepiece reticle for accurate
measurements it is
necessary to calibrate the eyepiece reticle using a stage
micrometer. A stage micrometer is typically a 1" x 3" slide with
a pattern of known dimensions on its surface. The stage micrometer
is placed directly on the stage of the microscope and brought
into focus. By rotating the eyepiece both scales can be
positioned parallel to each other. To calibrate the eyepiece
reticle you must first find out how many intervals of the
eyepiece reticle correspond to a certain distance on the
stage micrometer. You can then calculate the value of one
interval of the eyepiece reticle. Each microscope objective
must be calibrated independently.
Example: Let's say each division of the metric stage
micrometer above is 0.01mm or 10µ (10 micron). First determine how many divisions of the
eyepiece reticle correspond to a certain distance on the
stage micrometer and calculate the length of
one division of the eyepiece reticle. In this example 90
divisions of the eyepiece reticle corresponds to 60 divisions
of the stage micrometer. (Note: Even though it appears that more
than one set of lines are aligned, i.e. 30/20, 60/40 and 90/60,
it is typically most accurate to use the largest dimension pair
for your calculation.) Each division of the stage micrometer
equals 10µ, so 60 divisions of the stage micrometer would equal
600u. To calculate the value of one division of the eyepiece reticle
we would divide 600µ by 90 resulting in
6.67µ per reticle division. The reticle value, in this case 6.67µ,
would apply only to the objective for which the calibration was
made. Each microscope objective must be calibrated independently.
Important Note on Reticle Diameters & Patterns
All geometric patterns available will not fit on all available
reticle diameters! Please keep this in mind when choosing a
For example: The S-14368 Scale
Reticle is a 20mm scale. If you order it on a 19mm diameter
reticle you can see it will not completely fit. We
will assume this is done intentionally because you want
the pattern to go right to the edge. So, if you order this, we
will make it! Please be sure you completely
understand since these reticles are non-returnable!
If you have any doubt or questions at all, please contact us before ordering.
Custom Reticle and Stage Micrometer Designs
We are experts in making custom reticles and stage micrometers (or other similar products). If you need a reticle
or stage micrometer with an artwork design, physical dimension
or substrate material we don't normally consider standard we can usually still help. If you have your specifications ready just send them to us for a quotation, or we can assist you in developing the specifications that will satisfy your application.
RETICLES: Reticles with custom artwork have a minimum
one-time setup cost of $855 and $179.95/ea in small quantities.
These costs cover most designs we have seen, but
may increase depending on the complexity and size of the artwork, product dimensions
and requested substrate material. An exception is if we
can use a standard artwork pattern but simply remove some of the
can typically be done less expensively. Also, reticles using one of our standard
artwork patterns, but with a non-standard physical dimension or substrate
type, can usually be made less expensively as well since they
would not require new artwork. Please
contact us for a firm quote.
STAGE MICROMETERS: Prices for custom stage
micrometers vary significantly depending on your requirements
so you will need to contact us with
your details for a
quote. However, like the reticles above, any new artwork
requirement will have a minimum $855 setup charge. Please note: it is less expensive to put one of our
standard reticle patterns on a stage micrometer than to create