Voigtlaender & Sohn. Braunschweig. 141 



No. 2798. 



Voigtlaender & Sohn, Braunschweig. 



Optical Works. 



(Photographic Objectives, Binoculars and Terrestrial Telescopes.) 



The Optical Works of Voigtlaender & Sohn were founded by 

 Christoph Voigtlaender in Vienna in 1 756. In the days of the founder 

 and his son, Frederick, the principal business consisted in the manufacture 

 of spectacles, reading glasses, simple microscopes and hand-telescopes, in 

 particular those of the Galileo type. This, according to present views, 

 simple department of optical industry received a considerable impetus 

 when Frederick Voigtlaender in the beginning of this century began 

 to grind periscopical spectacle lenses and in 1811 constructed the first 

 Binocular on the principle of Galileo's telescope. At that time, however, 

 public requirements were too modest to encourage manufacture on a large 

 scale; at the same time the unsatisfactory quality and the optical unifor- 

 mity of the glasses which were then available and also the absence of 

 satisfactory mechanical means greatly impeded the development of optical 

 instruments. 



Not until Fraunhofer, in the first quarter of this century, taught 

 how to produce homogeneous gUsses capable of variation with respect 

 to their optical properties and suitable for optical combinations and how 

 to determine their optical constants with scientific precision, did it become 

 possible to make decided progress in the development of optical instruments. 



The third representative of the firm, Frederick Voigtlaender, 

 soon mastered and adopted Fraunhofer's methods and with a spectro- 

 meter, which he made himself, determined the refractive and dispersive 

 powers of all available glasses. This enabled him to compile optical data 

 for the computation of optical instruments; he utilised this knowledge 

 with the greatest success and supplied the mathematician Prof. Petzval 

 of Vienna with the data respecting the available glasses for the calculation 

 of a photographic doublet. According to the calculation of Prof. Petzval, 

 Frederick Voigtlaender, in 139, made the first photographic doublet 

 and thus inaugurated the era of photography, which within 50 years has 

 made greater strides in its development, in the improvements of the 

 methods and means which it envolves, and in the extension of its appli- 

 cation to the purposes of art and trade than perhaps any other branch, 

 of industry. 



The portrait lens, owing to its rapidity, furnished the first means 

 for the photography of living objects. It differed so much in its con- 

 structive elements and in its optical powers from any optical system 

 that had been produced previously, that it formed the basis of an entirely 

 new class of optical instruments. 



