diff --git a/src/consts.cu b/src/consts.cu
index 72733f6..fc9d1b9 100644
--- a/src/consts.cu
+++ b/src/consts.cu
@@ -52,3 +52,4 @@ __device__ float d_opacityK;
 __device__ float d_sigmoidShift;
 __device__ float d_sigmoidExp;
 __device__ int d_tfComboSelected;
+__device__ float d_opacityConst;
diff --git a/src/consts.h b/src/consts.h
index 239d58e..dcfa599 100644
--- a/src/consts.h
+++ b/src/consts.h
@@ -62,13 +62,15 @@ struct ColorStop {
     Color3 color;
 };
 
-// factor for the opacity function
+// factor for the gradient opacity function
 extern __device__ float d_opacityK;
 // sigmoid function variables
 extern __device__ float d_sigmoidShift;
 extern __device__ float d_sigmoidExp;
 // combo box index
 extern __device__ int d_tfComboSelected;
+// constant opacity option
+extern __device__ float d_opacityConst;
 
 const int lenStopsPythonLike = 5;
 const int lenStopsGrayscale = 2;
diff --git a/src/gui/input/Widget.cpp b/src/gui/input/Widget.cpp
index 8b9b2de..03f3a04 100644
--- a/src/gui/input/Widget.cpp
+++ b/src/gui/input/Widget.cpp
@@ -30,6 +30,7 @@ Widget::Widget(GLFWwindow* window) {
   this->sigmoidShift = 0.5f;
   this->sigmoidExp = -250.0f;
   this->tfComboSelected = 0;
+  this->opacityConst = 100;
 };
 
 // REFACTOR: should probably not have all the logic in one function; something like a list of ImplementedWidgets with each a Render() function (a la interface) would be better.
@@ -52,6 +53,7 @@ void Widget::tick(double fps) {
   ImGui::DragInt("Gradient exp. (log [1e-10, 1])", &this->opacityK, 1, 0, 100, "%d%%", ImGuiSliderFlags_AlwaysClamp);
   ImGui::DragFloat("sigmoidShift", &this->sigmoidShift, 0.01f, 0.0f, 1.0f, "%.2f");
   ImGui::InputFloat("sigmoidExp", &this->sigmoidExp, 10.0f, 100.0f, "%.0f");
+  ImGui::DragInt("Opacity constant (log [1e-5, 1])", &this->opacityConst, 1, 0, 100, "%d%%", ImGuiSliderFlags_AlwaysClamp);
   
   // the items[] contains the entries for the combobox. The selected index is stored as an int on this->tfComboSelected
   // the default entry is set in the constructor, so if you want that to be a specific entry just change it
@@ -118,6 +120,9 @@ void Widget::copyToDevice() {
   cudaMemcpyToSymbol(&d_sigmoidShift, &this->sigmoidShift, sizeof(float));
   cudaMemcpyToSymbol(&d_sigmoidExp, &this->sigmoidExp, sizeof(float));
   cudaMemcpyToSymbol(&d_tfComboSelected, &this->tfComboSelected, sizeof(float));
+
+  this->opacityConstReal = std::pow(10.0f, (-5 + 0.05 * this->opacityConst));
+  cudaMemcpyToSymbol(&d_opacityConst, &this->opacityConstReal, sizeof(float));
 }
 
 Widget::~Widget() {
diff --git a/src/gui/input/Widget.h b/src/gui/input/Widget.h
index 52727b3..c2fe991 100644
--- a/src/gui/input/Widget.h
+++ b/src/gui/input/Widget.h
@@ -23,6 +23,8 @@ public:
   float opacityKReal;
   float sigmoidShift;
   float sigmoidExp;
+  int opacityConst;
+  float opacityConstReal;
 
   ImGuiIO io;
 
diff --git a/src/illumination/transferFunction.cu b/src/illumination/transferFunction.cu
index a360602..0cb3271 100644
--- a/src/illumination/transferFunction.cu
+++ b/src/illumination/transferFunction.cu
@@ -62,7 +62,7 @@ __device__ float4 transferFunction(float density, const Vec3& grad, const Point3
     break;
 
   case 2:
-    alpha = 0.1f;
+    alpha = d_opacityConst;
     break;
   
   default: