Choosing The Correct Reticle Glass Diameter For Your Eyepiece

Choosing The Correct Reticle Scale Value For Your Objective

Calibrating Your Reticle With a Stage Micrometer

Important Note on Reticle Diameters & Patterns

Custom Reticle and Stage Micrometer Designs and Patterns

Choosing The Correct Reticle Glass Diameter For Your Eyepiece (top of page)

Most 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.

In 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" 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. The shelf is very important as it positions the reticle at the optical focal point of the eyepiece's 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. Be very careful you do not over-tighten this ring on the reticle as it may break or chip the reticle glass. Often you will need a spanner wrench of some kind 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 to 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 more likely it is not able to use 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.

If you have determined your eyepiece has the proper shelf inside the bottom of the eyepiece, 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 they may be in there.  This measurement must be reasonably accurate. It will typically be a fraction of a millimeter over a whole number. For example it may measure 19.6 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 / -0.005 in. so as long as the inside diameter of the eyepiece is between 0.1mm and 0.9mm larger than the reticle diameter it should fit.

Please note that a typical eyepiece will have numbers written on the outside such as WF10X/23MM. These numbers are not specifying the diameter of a reticle for that eyepiece. They are specifying the magnification of the eyepiece and its aperture size. 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 (top of page)

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.

Example 1: 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.

Therefore:
If you want 100 divisions: .003" x 100 divisions = .300"/100 div. (Part # S-14278)
If you want 200 divisions: .003" x 200 divisions = .600"/200 div. (Part # S-14299)

Below are examples of the different values attained from this reticle when used with various objective settings:

Part # S-14278: .300"/100 divisions, each division equals .003" actual value.
.003" @ 1x objective setting = .003" at target specimen.
.003" @ 2x objecting setting = .0015" at target specimen.
.003" @ 3x objective setting = .001 " at target specimen.

If you already have a reticle, use the following to determine its measurement resolution.

Example 2: You have a S-14340 reticle which has a 2mm scale divided into 200 divisions. Therefore each division is 0.01mm (10 micron). If you use the 40X objective lens on your compound microscope, you want to know the corresponding dimension of your target specimen.

Formula: Reticle Value / Objective = Value at Target Specimen.

0.01mm / 40 = 0.00025mm (0.25 micron or 0.25µ)

Below are examples of different values attained from this reticle used with various objective settings.

Part # S-14340: 2mm/200 divisions, each division equals 0.010mm actual value
0.01mm / 4 = 0.0025 (2.5µ) at target specimen.
0.01mm / 10 = 0.001 (1µ) at target specimen.
0.01mm / 100 = 0.0001 (0.1µ) at target specimen.

Calibrating Your Reticle With a Stage Micrometer (top of page)

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 on which a scale has been etched. The eyepiece reticle is inserted into one eyepiece and held in place in the correct focal plane of the eyepiece. 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 simply a microscope slide with a pattern of known dimensions etched upon 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). The eyepiece reticle is divided into 100 units. First determine how many divisions of the eyepiece reticle correspond to a certain distance on the stage micrometer and calculate the length which corresponds to one division of the eyepiece reticle. In this example 30 divisions of the eyepiece reticle corresponds to 20 divisions of the stage micrometer. Each division of the stage micrometer equals 10µ so 20 divisions of the stage micrometer would equal 200u. To calculate the value of one division of the eyepiece reticle we would divide 200µ by 30 and the result would be 6.67µ per 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 (top of page)

All geometric patterns available will not fit on all available reticle diameters! Please keep this in mind when choosing a reticle/geometry combination.

For example: The S-14368 Scale Reticle is a 20mm scale. If you order it on a 17mm diameter Reticle, you can see that it will not completely fit.  We understand that sometimes this is intentional because you may want the geometry to go right to the edge. So, if you order this, we will make it! How will we orient the pattern on the glass? Unless you tell us otherwise we would do it just as if it was being printed on a larger diameter piece of glass. The center of the geometry will be in the center of the glass. Therefore in the above example, both ends of the pattern will fall off the edge. We can orient it differently (left justified for example), but you would need to contact us before ordering to make sure we know what you want. Please make sure you completely understand what you will be getting since these types of reticles are non-returnable! If you have any doubt at all, please call us.

Custom Reticle and Stage Micrometer Designs (top of page)

We are capable of making custom products if you need a reticle or stage micrometer with an artwork design, physical dimension or substrate material that we do not carry as standard.  Unless the design is very simple, we will need you to supply us with an artwork drawing and any other differing specifications. 

RETICLES: Reticles with custom artwork have a minimum cost of $715 for setup and $125/ea in small quantities.  These prices cover most designs we have been asked to do, 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 design. This 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.