Selecting the Correct Eyepiece Reticle

There are two things that need to be defined when selecting your reticle:
1. The pattern that is suitable for your application
2. The diameter required to fit your eyepiece

The Pattern

The application or method that you are working to will normally determine the reticle pattern that will be required. For instance, if you are doing straight forward length measurements you may require a simple horizontal scale, if you are performing asbestos analysis you are most likely to need a Walton & Beckett reticle.

One very common mistake that is made when selecting the reticle is with the size of the pattern. If you have a 10mm length scale (such as our NE1) in the eyepiece this does not mean that it will measure 10mm at the specimen stage. You have to take into account the objective magnification.

Here is a formula that should help you select the right pattern:

Actual Size on Reticle / Objective Magnification = Size at the Stage

Table showing an example with one micron measurement at stage and relating size at image plane/reticle depending on objective magnification used:

Measurement at Stage Objective Magnification Size at Image Plane/Graticule
Measurement at Stage Objective Magnification Size at Image Plane/Graticule
0.001mm (1um) 1.25X 0.00125mm (1.25um)
0.001mm (1um) 2X 0.002mm (2um)
0.001mm (1um) 5X 0.005mm (5um)
0.001mm (1um) 10X 0.010mm (10um)
0.001mm (1um) 20X 0.020mm (20um)
0.001mm (1um) 40X 0.040mm (40um)
0.1mm (100um) 4x 0.4mm (400um)
0.1mm (100um) 10x 1mm
0.1mm (100um) 20x 2mm
0.1mm (100um) 40x 4mm
0.1mm (100um) 100x 10mm
1mm 4x 4mm
1mm 10x 10mm
1mm 20x 20mm


The Diameter

The diameter of the reticle is important to ensure it fits the eyepiece you have. We have compiled a database of various manufacturers, eyepieces and the size of reticle required to fit them. Click on this link for this database. 

If your eyepiece reference is not in this database, we have created a guide and video to help you measure and define the right reticle diameter for your eyepiece. Click here to download our guide or here to view our video.



All About Eyepiece Reticles

Technical Guide – Eyepiece Reticles


  • Reticle, Reticule and Graticule are all words used to represent the same thing in light microscopy. It is a circular glass disc which has a pattern or scale marked onto its surface and is fitted in the eyepiece (ocular) of a microscope. When you look down the eyepiece the image on the reticle is superimposed over the specimen image so that measurements, comparisons, or counts can be made. 


  • The selection of the Reticle type (pattern) will depend on the application or analysis being done. Many analysis methods will specify the type of reticle required. For instance, the measurement and counting of asbestos fibres will inevitably require a Walton and Beckett pattern. Likewise, many ASTM or ISO tests will suggest the reticle to use.
  • For general applications such as measurements and cell counting there are numerous types that could be used so the deciding criteria is likely to be the size of the specimens and/or the magnification being used.
  • The fundamental thing to remember is that the size of the reticle pattern will make measurements at the stage that are determined by the objective magnification. For instance, if you want to measure 1mm at the specimen stage and you are using a 10x objective lens, then the size at the reticle plane in the eyepiece will be 10mm (simply 1mm x 10). This will be true for all sizes/magnifications, you just multiply the size you want to measure by the objective magnification to see the size that it will appear in the eyepiece, you can then select the reticle that has a pattern of that magnified size.