Focusing

Presentation made to the Société Française de Photographie during the session of December 7, 1894

When, during an excursion, one has used up all the plates in their camera, one might want to continue the photographic series.

In the cameras I supply equipped with Hanau-F.-M. Richard mobile magazines, it is enough to replace the depleted magazine with a new one. However, in some other cameras, such as the Carpentier Photo-Jumelle, whose plate reservoir is fixed to the instrument, another method is necessary.

The oldest recommended method involves using a sleeve made of inactinic fabrics, inside which one replaces the exposed plates with new ones by feel, a relatively easy task.

A new, very ingenious method has been created by Lieutenant Rimailho. It involves using wooden boxes preloaded with gelatino-bromide plates in small metal frames.

The photo-jumelles, having received on the side in our workshops a small, barely noticeable ebonite piece with a sliding trap door, are loaded and used as usual. When all the plates are exposed, proceed to unload as follows:

Take an empty loader (a small wooden box with a sliding trap door on one side and two hooks, one of which is spring-loaded), attach it to the jumelle as shown in the accompanying figure, with the trap door at the bottom, the two trap doors against each other (the spring hook should make a clear snap).

Then open: 1° the trap door of the jumelle, 2° the trap door of the loader.



Holding the camera as shown in the figure, preferably more inclined rather than less, pull the plate change rod and push it back twelve times. Each time, a frame with its plate passes from the photo-jumelle into the loader.



When all the frames are in the loader, close the loader's trap door and detach it.

To reload the now-empty photo-jumelle, take a loader pre-filled with frames and plates, attach it in the same way to the photo-jumelle and proceed as follows:
Straighten the photo-jumelle as shown in the figure below, pull the plate change rod and push it back fully.



Open the loader's trap door (the photo-jumelle’s trap door remains open), then, with a swinging motion, straighten the loader upwards. In this movement, the frame at the bottom of the loader passes, by its own weight, from the loader into the photo-jumelle. Return everything to horizontal so the frames descend inside the loader, then straighten and a second frame passes into the photo-jumelle. Continue this oscillation up to the eleventh plate.

At this point, pull the drawer rod of the photo-jumelle fully, as for a plate change, and make the twelfth plate pass from the loader into the photo-jumelle with one last oscillation. Push back the drawer, close both trap doors and detach the loader.

The photo-jumelle is reloaded.

The description of these operations takes longer to read than to do, as it only takes about a minute.

**Note:** To ensure the frames transferred from a loader to the photo-jumelle are correctly ordered by their numbers, the loader should be filled as follows in the laboratory:

Place the loader flat on the table, in front of you, with the hooks facing the right side. Open the trap door, now at the top, with the operating tab below, on the table.

Take frame No. 12, insert the sensitive plate, slide it into the loader with the heel back, the number on top, readable correctly, the plate below, then place frame No. 1, then No. 2, and so on up to No. 11, which is the last one. Then close the trap door.

The operation is as simple as possible.