Bardou telescope

The telescope, produced by Denis Albert Bardou, “fournisseur du Ministère de la Guerre, du Ministère de la Marine et des Gouvernements étrangers”, was adopted by the French Army and used by the Bulgarian fortress-siege artillery between the end of the 19th and the beginning of the 20th century. There are two different model of military telescope (lunettes militaires): N° 1 with a magnifying power of 15 times, a lens diameter of 29mm, a length of 17cm close and 33cm developed; N° 2 with a magnifying power of 30 times, a lens diameter of 34mm, a length of 19cm close and 45cm developed. The Bulgarian Army adopted the first model.
The Bardou telescope was an ordinary telescope, with a vertical scale of divisions engraved on one of the lenses of the eyepiece tube. These divisions were numbered from bottom to top from 4 to 0 and from 0 to 12. A thin and long horizontal line passed through the divisions 0 and 4. To the right and left above the horizontal zero line there was a scale of divisions, arranged in a column and numbered on the right side with the numbers 0.6, 1, 3, 4 and 5 and marked with the letter C (for cavalry), and on the left with the numbers 0.8, 1, 2, 3, 4 and 5 and marked with the letter F (for infantry). The width of the divisions of the vertical column of the scale is such that the angular unit of a division corresponds to 4’. The telescope was placed on a tripod stand, which allows it to be rotated horizontally and vertically.
Use of the Bardou telescope The Moller device could be used to determinate : a) the height of the shrapnel bursts; b) the lateral deflection of the projectiles; c) the distance to the target if its width was known or the width of the target if its distance was known. When using the vertical scale of the telescope the observer proceeds as with the Moller device. The F and C scales were used to determine the distance to the target whether it was infantry or cavalry. For this purpose, the zero line of the scale was directed to the base (feet) of the infantryman or of the horse and the observer looked at which division lined up with the top of his head: this division multiplied by 1000 gave the distance to the target.
SOURCES : - Ръководство за занятията въкреспостата артилерия. Част IV. Подготовка и служба на наблюдателите, Sofia 1902, pp. 32-34; - MAISON BARDOU – VIAL. J. : Instrument d’optique. Catalogue 1899, La Rochelle 1899, p. 15.