In June 2, 1888,  Edouard Derogy filed the patent No. 190.172 for a « Chambre photographique portative » for 12 views on 9 x 12 cm plates.
This camera was called « Le Photo Secret », but the brand was not filed.
It is a camera in the form of a wooden box measuring 27 x 16 x 23 cm and comprising inside :
 

• A hyperfocal lens (but could be replaced by a more complex lens according to the author )
• a rotary shutter and its movement control ,
• a removable plate casing with two superimposed compartments , one above for blank plates , the bottom one receiving the exposed plates.

The plates are placed individually on light metal sheet holders , and then slid vertically one behind the other in the grooves of the upper tray . ( rep.8 , fig 2 of the patent ) .
When the picture is taken , the manipulation of the lever ( 13) on the right rear of the device opens a door (17) in the floor separating the two stores : the exposed plate falls into the lower compartment ( 9).
A knurled knob (10) placed below the lever moves with racks the plates casing until the next blank plate is placed at the focal plane of the lens . The indication of the plate number appears in a small opening.
These plates casings are closed by flaps provided with velvet strips to prevent from any light ingress in the casings.

The camera has two brilliant viewfinders and two tripod sockets and two nuts to allow horizontal or vertical views . In "normal" position , that of the photo, the camera takes horizontal pictures.
In front of the right side are placed from top to bottom :
 

• T or I selector,
• the shutter speed selector ,
• the shutter release.

They are surrounded by a polished brass plate engraved « Le Photo Secret, Derogy, BSGDG ».
The lens is fully inside the camera and the front opening can be closed by a sliding plate .
The shutter is actuated by a spring whose cocking key ( 20 ) is placed in the center of the front panel: The manufacturer said it allows at least 12 images.
The shutter is a large metal plate (6 ) with two openings : it  makes a ½ turn after each photo is taken.
For T exposure, the disc is stopped by a stop ( 36) hitting a rod moved before shooting . It is released by pulling back the rod.
The rotational speed of the shutter disk , so the time of exposure of the sensitive plate is adustable by a friction device ( fig. 4 ) on one of the pinions ( 27 ) of the mechanical movement , controlled by a lateral graduated selector .
The diaphragms are of blackened brass, valve type, placed inside the optical block, between the lens .