Development telemetric

The developped at the telemetric point is based on an instrument being in the camera: the rangefinder. The name “rangefinder” comes from “tele” distance and “meter” measures, for “remote measurement” but also “measurement of distance”. This apparatus makes it possible to measure the distance between its position and a point concerned without it being necessary to move towards the measured point.

Telemeter with coincidence of image

The rangefinder is made of two windows of aiming whose distance forms the “base”. The images of these two windows are brought on the same eyepiece by a set of mirrors. When an object is aimed at, one sees by the eyepiece two shifted images of the object. One operates an order which makes it possible to superimpose these two images. The distance is then read on a graduation of the order. In fact one measures the angle centered on the point concerned and thus the sides pass by the windows of aiming.

This apparatus is as well used out of artillery as in photography.

On the cameras with development telemetric, this rangefinder is coupled with the adjustment of the development of the objective .

This mode of development is appreciated for its precision, in particular when it is used with optics great angle, luminous or used in weak luminosity. On the other hand, it is appropriate badly for the long focal distances, when the relationship between the distance from development and the base becomes too weak.

This mode of development was almost completely replaced by the aiming reflex camera and the autofocus.

The most known manufacturer of telemetric apparatuses is Leica and its series “M”, whose numerical version, the Leica M8, was marketed in 2006.

Telemeter with coincidence of line (system Dodin)

The image of the point concerned is shifted towards the right-hand side and the left by two prisms fixed on glass of aiming. The shift is null when the image is developed (clear) in the plan of the prisms.

This system, which almost equipped all the cameras reflex camera before the invention with the development automatic, is very precise when the light is sufficient, but functions badly in low light and requires luminous objectives.

It is easily recognizable with the clearly barred circle of a visible diameter in the sight.

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