Comparison Microscopy

Comparison of marks found at scenes of crime with test marks made by implements thought to be responsible for them is a well-established and valuable source of scientific evidence. If the marks are small or show fine detail they may be examined by optical microscopy using a comparison bridge to display the images of the unknown and test marks side by side.

Optical microscopy is simple, though the process of comparison requires a great deal of skill. The samples can be manipulated easily and since comparisons are mostly made at low magnification the resolution is more than adequate. Because of the limited depth of field however, examination of large areas of rough or curved surface is difficult and photographs do not show corresponding points clearly.
Those not familiar with comparison microscopy cannot interpret the pictures and this may be a serious shortcoming when they are presented in court.

The Scanning Electron Microscope has a great depth of field and can produce striking images over a wide range of magnifications on rough or curved surfaces.

In order to compare two samples simultaneously the reference image from one is held in a digital image store. The second sample is then scanned in real time whilst a segment of the stored image is overlaid and by a combination manipulating the positional controls and magnification the markings on each image can be accurately compared.

CamScan supply special sub-stages to give the operator the ability to rotate or tilt the sample in addition to the standard 5-axis stage controls on the fully eucentric specimen stage.