Schneider field gun sight

The Schneider field gun was equipped with collimateur with aiming circle and a spirit level mounted on a special support that could be easily mounted on the gun. The sighting apparatus was not placed on top of the arc sight, as in the German guns, but on a separate pedestal, mounted on a bar actuated by the laying wheel, independently of the elevating wheel.

The collimateur C consisted of a block of clear glass about 70 mm long by 10 mm square, and could be moved around an axle parallel with the axis of the trunnions. The front face was blackened, except for a cross of clear glass while the rear face was ground like a lens. When the eye was placed about 30 cm behind the sight, and in the optical axis of the lens, the layer could see before him a white cross on a black ground. The apparent distance of the cross was 1 m, so that the collimateur gave a sighting radius equivalent to that of a rocking-bar one metre long. This was known as an optical, in contradistinction to a real, line of sigh. To use the collimateur, the layer kept his eye about 30 cm behind the eye-piece, looked alternately at the object and at the cross, and worked the elevating handwheel G and traversing crank m till he brought first the horizontal line and then the vertical line to coincide with the object.

The spirit level N was used to obtain the angle of sight. It was put in the correct position shown on the sector ∑¹ by means of the milled head B¹. When the level difference was too great and ∑¹ the scale was insufficient, the layer moved slightly the collimateur by means of the milled head B², and read the additional correction on the scale ∑². To correct the little errors due to the breaking down of the gun, the air bubble should be constantly brought back between its marks. The spirit level could also be used to calculate the slope of the trunnions, turning 90° the movable wheel where it was placed.

The sighted ruler was pivoted on the aiming circle (goniometer) P, a circulated graduated base-plate, with every quadrant divided in 100 parts. A drum T, by means of an additional shifting of the pillar, permitted to obtain an azimuthal direction expressed in millièmes.

SOURCE :

- BETHELL. Henry Arthur : Modern Guns and Gunnery, 1910. A Practical Manual for Officers of the Horse, Field and Mountain Artillery. Woolwich : F.J. Cattermole 1910, pp. 88;

- CUREY. Charles Marie : “L’artillerie Schneider-Canet à l’Esposition universelle de 1900”. Revue d’artillerie : LIX (Octobre 1900 – Mars 1901), pp. 147-148.

The collimateur C