diff --git a/export/config.py b/export/config.py
index 798e0c9f..56680044 100644
--- a/export/config.py
+++ b/export/config.py
@@ -121,13 +121,15 @@ def _convert_opencl_settings(scene, definitions, is_final_render):
 def _convert_viewport_engine(scene, definitions, config):
     _convert_path(config, definitions)
 
-    use_cpu = scene.luxcore.viewport.device == "CPU"
+    viewport = scene.luxcore.viewport
+
+    use_cpu = viewport.device == "CPU"
     if not use_cpu and not utils.is_opencl_build():
         msg = "Config: LuxCore was built without OpenCL support, can't use OpenCL engine in viewport"
         scene.luxcore.errorlog.add_warning(msg)
         use_cpu = True
 
-    resolutionreduction = 4 if scene.luxcore.viewport.reduce_resolution_on_edit else 1
+    resolutionreduction = viewport.resolution_reduction if viewport.reduce_resolution_on_edit else 1
 
     if use_cpu:
         luxcore_engine = "RTPATHCPU"
diff --git a/properties/viewport.py b/properties/viewport.py
index a8253c22..8c922568 100644
--- a/properties/viewport.py
+++ b/properties/viewport.py
@@ -38,6 +38,9 @@ class LuxCoreViewportSettings(bpy.types.PropertyGroup):
     reduce_resolution_on_edit = BoolProperty(name="Reduce first sample resolution", default=True,
                                              description="Render the first sample after editing the scene "
                                                          "with reduced resolution to provide a quicker response")
+    resolution_reduction = IntProperty(name="Block Size", default=4, min=2,
+                                       description="Size of the startup blocks in pixels. A size of 4 means that "
+                                                   "one sample is spread over 4x4 pixels on startup")
 
     use_bidir = BoolProperty(name="Use Bidir in Viewport", default=True,
                              description="Enable if your scene requires Bidir for complex light paths and "
diff --git a/ui/viewport.py b/ui/viewport.py
index 1bae8f19..6cbcf25e 100644
--- a/ui/viewport.py
+++ b/ui/viewport.py
@@ -18,7 +18,12 @@ def draw(self, context):
         viewport = context.scene.luxcore.viewport
 
         layout.prop(viewport, "halt_time")
-        layout.prop(viewport, "reduce_resolution_on_edit")
+
+        split = layout.split(percentage=0.6)
+        split.prop(viewport, "reduce_resolution_on_edit")
+        sub = split.row()
+        sub.active = viewport.reduce_resolution_on_edit
+        sub.prop(viewport, "resolution_reduction")
 
         col = layout.column()
         col.prop(viewport, "pixel_size")