diff --git a/src/openflexure_microscope_server/things/camera/__init__.py b/src/openflexure_microscope_server/things/camera/__init__.py
index 14088f21..6b9bc323 100644
--- a/src/openflexure_microscope_server/things/camera/__init__.py
+++ b/src/openflexure_microscope_server/things/camera/__init__.py
@@ -274,7 +274,7 @@ class BaseCamera(lt.Thing):
             "CameraThings must define their own capture_array method"
         )
 
-    downsampled_array_factor: int = lt.property(default=2)
+    downsampled_array_factor: int = lt.property(default=2, ge=1)
     """The downsampling factor when calling capture_downsampled_array."""
 
     @lt.action
diff --git a/src/openflexure_microscope_server/things/camera/simulation.py b/src/openflexure_microscope_server/things/camera/simulation.py
index 31e3979e..5db72b8b 100644
--- a/src/openflexure_microscope_server/things/camera/simulation.py
+++ b/src/openflexure_microscope_server/things/camera/simulation.py
@@ -172,6 +172,8 @@ class SimulatedCamera(BaseCamera):
 
     @blob_density.setter
     def _set_blob_density(self, value: int) -> None:
+        if value < 0:
+            self.logger.warning("Sample density must be >= 0")
         self._blob_density = value
         if self._capture_enabled:
             self.generate_canvas()
@@ -457,7 +459,7 @@ class SimulatedCamera(BaseCamera):
             return self._capture_thread.is_alive()
         return False
 
-    noise_level: float = lt.property(default=2.0)
+    noise_level: float = lt.property(default=2.0, ge=0)
 
     def _capture_frames(self) -> None:
         last_frame_t = time.time()