Early Achromatic Chest Microscope, ~1805


Analyses of the optical system

© Microscope History all rights reserved

The early achromatic chest microscope came with an assemblage of objectives and other components of optical parts. Two objectives (A, B, seen above with their inner parts dismantled) were achromatic, another three (C, D, E) were non-achromatic. The role of the other brass components is unclear. The two achromatic objectives contain each a small cylindrical tube, each one of which contains one doublet (see below). In objective A the cylinder slides freely into the tube while in objective B it screws into the end of it. Four discoidal lenses fitting the internal diameters of the tubes were found, two were still inserted into objective A. It was unclear whether each two of the lenses were originally inserted into each objective, or whether all four of them originally came from one of them. All four lenses bear a film of some sticky matter on one side, now blackened with dirt. Therefore, they may have been glued to each other in the past in pairs by some optical resin and inserted into the objectives.

The two composite objectives were dismantled and their internal brass cylinders containing the assumed doublets, as well as the four free lenses, were taken out. The internal lenses within the brass cylinders were held in place by brass circlips (photo below), and it was decided to open only the one from objective B. It contains two lenses, dry-set together, one is double convex and the other is a double-concave cylinder. No glue or balsam was holding these lenses together.

The results of the chemical analysis of the lenses are provided in the table below. The "Balance" is the concentration of the light elements of atomic number 1-11, which the portable XRF is incapable of identifying. The ± sign refers to the limits of detection for each element.

Physical and chemical analyses of the lenses

The optical components were subjected to scientific analyses in the Laboratory for Microarchaeology at the Ben Gurion University of the Negev, Israel. Non-intrusive elemental analysis of the lenses was carried-out using a Niton™ XL3t GOLDD+ XRF Analyzer set to the "Mining" calibration, providing a list of elements from Mg to U. Screening was made for 30 seconds per "filter", summing up in 120 seconds for each analysis. The data was set to be displayed in weight percent. These tests were aimed at providing some preliminary information about the optical system, first and foremost to clarify if it is indeed made of achromatic doublets and if so, try to reconstruct its general setting.

The lenses were photographed under a Zeiss Stemi-2000 stereomicroscope equipped with upper LED ring illumination. 

Lens 4





© Microscope History all rights reserved

© Microscope History all rights reserved

© Microscope History all rights reserved

© Microscope History all rights reserved

The elemental concentrations of the lenses indicate that while the double-convex lens of the doublet in objective B is made of high silica-lime "crown glass", the double concave cylindrical "negative" lens attached to it was made high lead-alkaline + silica "flint glass". This clearly testifies to an achromatic doublet of an early and very simple type. The four free lenses bearing the resin/balsam remains were all found to be of a more or less similar composition, all being made of crown glass but with somewhat lower contents of calcium (Ca) as compared with the "positive" lens from the doublet.

Molecular study of the coating on the lenses

The resin remains were attempted to be analyzed using a Rikagu™ Progeny ResQ 1064nm handheld Raman spectrometer. The aim of this study was to reveal the composition of the matter remains coating lenses 1-4.

The Raman indicated that the four lenses were coated by "gum Sandarac", namely turpentine made from tree resin. It indicates that the lenses were glued (presumably in couples) by an optical-quality mounting resin. 

© Microscope History all rights reserved

Copyright © 2015-2020 microscopehistory.com . All Rights Reserved.