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 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:
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 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 to help you measure and define the right reticle diameter for your eyepiece. Click here to download our guide.