- 01: Introduction
- 02: History
- 03: Propellants, Firearms, and Ammunition Development
- 04: Modern Firearms Manufacture
- 05: Small Arms Ammunition
- 06: Evidence Handling Procedures
- 07: Equipment and Instrumentation
- Introduction
- Objectives
- AFTE Knowledge and Ability Factors
- Measurement, Standards, and Accuracy
- Weight, Force, and Their Measurement
- Dimensional Data and Measurement Tools
- Muzzle Velocity of Bullets
- Stereo and Comparison Microscopes
- Small Tools and Supplies
- Imaging Equipment
- Field Support Equipment
- Computer-Based Technologies
- Firing Facilities
- Selected Bibliography
- 08: Examination of Firearms
- 09: Cartridge and Shotshell Examination
- 10: Characterization and Evaluation of Fired Projectiles
- 11: Bullet Comparison and Identification
- 12: Gunshot Residue and Distance Determination
- 13: Toolmark Identification
- 14: Communicating Results
- Resources
Glass Measuring Reticules
Home > Equipment and Instrumentation > Dimensional Data and Measurement Tools > Glass Measuring Reticules
Measuring reticule accessories have been available for many decades. They are compatible with microscope eyepieces, or may be integral parts of an eyepiece micrometer. These glass reticules are easily put in place by insertion into a reticule holder on the underside of an adjustable stereomicroscope eyepiece. Reticules can be provided in a variety of standard measurement divisions (such as inches or millimeters), as needed. It is important to note that both eyepieces of a stereo microscope must be adjustable to use this technique. Calibration must be carried out using a stage micrometer, which is a glass slide with known divisions for use as a standard.
Filar Micrometer Eyepieces
A filar micrometer eyepiece is a specialized optical instrument for taking linear measurements directly through a microscope. (The word filar is derived from the Latin word filum, or thread.) The micrometer eyepiece is substituted for a standard eyepiece on stereo and comparison microscopes and is
used to measure the widths of land and groove impressions in fired bullets and small evidence items.
The filar micrometer eyepiece is an optical-mechanical system, which includes several components:
- A tube to replace a standard microscope eyepiece
- A focusable eyepiece
- A stationary optical scale inserted within the eyepiece to optically anchor on a point to be measured
- A movable optical hairline or thread within the field of view superimposed on the stationary standard
- A manual micrometer screw which moves the optical hairline from starting to end point of the item being measured, with an analog vernier scale for reading results
Digital filar eyepieces translate the mechanical movement of the optical hairline into a digital readout. A specialized processor is required and costs ten to fifteen times as much as manual calculation.
Electronic Reticules
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A microscope being used with
electronic reticle software
Electronic reticules for stereomicroscopes are a recent addition to the measuring equipment available to forensic examiners. They combine a stereomicroscope, a digital camera, and a computer. Live images are displayed on-screen with a choice of measuring grid (electronic reticule) overlays, providing a convenient method for taking and comparing measurements. The software saves and exports the image data for use in case documentation.
Striations on a bullet through
an eyepiece reticle
Eyepiece Measuring Reticules
Older comparison microscopes may be fitted with glass eyepiece reticules. It is difficult to find appropriate glass reticules for these microscopes because neither the microscopes nor the reticules are being manufactured.
