Reticles and Eyepiece Micrometers

straight line reticle for microscope

Reticles are clear circular glass inserts with a scale inscribed on them.  They sit right at the focal plane inside the eyepiece lens of the microscope and allow the investigator to make accurate measurements of specimens.  In a stereo or binocular microscope, there will only be one reticle in one of the lenses.  The lens that holds the reticle must have a reticle retainer and the reticle must be of the proper diameter for the particular eyepiece lens.  Most of our microscopes are capable of accepting a reticle (23mm diameter for the stereos and 19mm diameter for the compound microscopes).  They are generally mounted in a 10x eyepiece lens.

If you purchase a microscope with a reticle installed in one of the eyepiece lenses, you might also wish to purchase a separate lens without the reticle.   You can then switch lenses whenever you want a clear field of view.

Straight Line Reticle
microscope reticle ring

Mounting the reticle is a somewhat critical operation.  Reticles are relatively simple to install but since they sit right on the focal plane, any dust on the reticle will be quite apparent when looking into the microscope.  To install a reticle, you simply spin out the retainer ring with a small screwdriver, install the reticle then re-install the retainer ring.  We recommend cleaning the reticle with lens tissue and using compressed air to blow out any dust after installing it.  Extra care should be taken with the eyepiece lens whenever it is removed from the microscope and make sure you undo the reticle ring and not the ring that holds in the lenses!

Reticle Retainer Ring
microscope lens

Reticles can be found on our website by typing "reticle" into the search bar, or simply calling us and letting us know what you need - we are happy to help you find the right reticle. We also can help you get a custom-made reticle if necessary. There are a wide variety of reticles available including reticles with circles, squares and various grid patterns. 

The "actual" distance between any two marks on the reticle is a function of the objective lens only.  The best way to calibrate your reticle is to use a stage micrometer.  A stage micrometer is a microscope slide that has tiny marks of a known dimension inscribed on it.  By making a comparison of the marks on the stage micrometer to the marks on the reticle, one can establish the actual value for each mark on the reticle. This is known as calibrating the microscope.  We also carry stage micrometers for both stereo and compound microscopes.   

Looking inside at retainer ring.
microscope reticle view
In microscopy, a measurement called the micrometer is used.  There are 1000 micrometers (abbreviated um) in one millimeter.  In the picture at the left, you see a typical reticle.  It is called a "straight line" reticle and is 10mm long with 100 divisions.  Each division therefore is one tenth of a mm.  This is represented as 0.1mm or 100 micrometers (um).  For a 1x objective, these measurements should be true and each division would represent 0.1mm.  As we change to higher objectives, the value of the distance between each line becomes less.   You can get a rough idea what each line represents at various powers by looking at the chart below. These are just approximate.  A stage micrometer should be used for accurate calibration of the reticle.

View through the eyepiece using a reticle.

The magnifying power of your eyepiece lenses do not enter into the equation. To learn how to properly calibrate your reticle with a stage micrometer, visit this page.

1x objective 100um
4x objective 25um
10x objective 10um
40x objective 2.5um
100x objective 1um