diff --git a/backend/camera.py b/backend/camera.py
index 2e9f1c6..94f1917 100644
--- a/backend/camera.py
+++ b/backend/camera.py
@@ -330,6 +330,18 @@ class Camera:
         except Exception as e:
             log.warning(f"Viewfinder non supporté : {e}")
 
+    def keepalive(self) -> bool:
+        """Envoie une commande legere au Canon pour empecher l'auto power off.
+        Utilise get_config qui declenche internement ptp_canon_eos_keepdeviceon."""
+        if self.mode != "gphoto2" or not self.connectee or not self.camera:
+            return False
+        try:
+            with self._gp_lock:
+                self.camera.get_config()
+            return True
+        except Exception:
+            return False
+
     def _preview_gphoto2(self) -> bytes | None:
         try:
             with self._gp_lock:
diff --git a/backend/main.py b/backend/main.py
index 10a8a12..725393f 100644
--- a/backend/main.py
+++ b/backend/main.py
@@ -61,10 +61,13 @@ _preview_none_count = 0
 _PREVIEW_GRACE_FRAMES = 40  # 40 x 50ms = 2s avant de declarer une erreur (Canon LiveView peut être lent à démarrer)
 
 
+_derniere_keepalive = 0.0
+
 def _thread_preview():
     """Thread de fond : capture les frames DSLR en continu.
-    Tourne TOUJOURS quand le DSLR est connecte pour maintenir le miroir leve."""
-    global _derniere_frame_preview
+    Tourne TOUJOURS quand le DSLR est connecte pour maintenir le miroir leve.
+    Envoie un keepalive PTP toutes les 30s meme quand le preview n'est pas actif."""
+    global _derniere_frame_preview, _derniere_keepalive
     while True:
         try:
             if capture_en_cours or camera.mode != "gphoto2" or not camera.connectee:
@@ -74,9 +77,14 @@ def _thread_preview():
                 donnees = camera.preview()
                 with _preview_lock:
                     _derniere_frame_preview = donnees
+                _derniere_keepalive = time.time()
             except Exception:
                 with _preview_lock:
                     _derniere_frame_preview = None
+                # Preview echoue → keepalive de secours via get_config
+                if time.time() - _derniere_keepalive > 10:
+                    camera.keepalive()
+                    _derniere_keepalive = time.time()
             time.sleep(0.033)  # ~30 fps max
         except Exception as e:
             log.error(f"_thread_preview crash: {e}")