Comparison Microscope

✔Since the invention of the microscope has been carried out it has undergone many changes in size shape and design. The most commonly used microscope is with a single eyepiece and is called the monocular microscope with a vertical body tube.

✔To avoid fatigue to the neck and the back the microscope was fitted with an angular or an inclined drawtube. Also, the inclined draw tubes were made fully rotatable to 360゚. To enable more than 1% to view the object without changing the seat just by rotating the drawtube neck.

✔Then come the inclined binocular microscope which enables the viewers to observe with both the eyes and hence reducing the tiredness of the observers.

✔The trinocular microscopes are now available with a binocular head with an extra vertical draw tube attached to it which helps in photomicrographic work.

🔬The forensic microscopy required a side-by-side comparison of the question and specimen sample. This kind of examination is best performed with the help of a comparison microscope.

🔬The device used to analyze side-by-side specimens.

🔬It is two microscopes connected by an optical bridge which enables two separate objects can be viewed side by side at the same time.

🔬 The comparison microscope offers a simultaneous examination of both the sample under observation. The basic construction is a combination of two compound microscopes joined together to form one single unit.

🔬The unique feature of its design is that it has a bridge incorporating a series of mirrors and prism to join two independent objective lenses into a simple unit.

🔬 The optical characteristics of both the objective lens must be as closely matching as possible to obtain the same magnification with minimum distortion of the image.

🔬The observer look through the eyepiece as in the case of a regular microscope except for the presence of a line in the middle that separates the circular field of view into the parts.

🔬The left side of the view is the image produced by the left microscope and the right side of the view is the image produced by the right microscope.

History

• The comparison microscope was first invented by Sir Calvin Goddard who was a US army colonel who was working with the bureau of forensic ballistics in New York.

• In the 1920s a Swedish criminalistic Harry sadder man improved the design of the comparison microscope by inventing the system of rotating bullets under the objective lens. Soderman gave the name hysteroscope to his invention.

• Philip O. Gravelle developed the comparison microscope for the identification of fire bullets and cartridge cases under the guidance of Calvin Goddard.

Comparison Microscope

Working Principle

• Two microscopes are placed next to each other and the optical path of each microscope is connected with an optical bridge.

• That optical bridge is having series of lenses and a mirror that brings two images back together at a single eyepiece.

• The observer simply looks to the microscope and a line separates two objects under examination.

• Advanced and modern comparison microscopes give the facility to superimpose the image.

Application

The comparison microscope can be used for the examination of physical evidence provided that it should have some unique morphological characteristics.

In general, the comparison microscope is used for the analysis of:

• In forensic ballistics for comparison of fired bullets and cartridge cases.

• It can be used for the study and comparison of tool marks.

• It is used for the comparison of various biological evidence like hair samples, pollen grains, diatoms, and fibers.

• It is used in questioned documents examination for the comparison of ink various marks present on the document.

• It is used for the split image comparison of currency notes or banknotes.

• It can also be used for comparing paint chips, fragments of glass, soil particles, etc.

• It is used for comparison of ejector or extractor marks.

Limitations

• This microscope is very costly.

• It requires very accurate handling.

• The person using the device must be an expert.