diff --git a/rtengine/filmnegativeproc.cc b/rtengine/filmnegativeproc.cc
index f5a231c05..eed10fdc4 100644
--- a/rtengine/filmnegativeproc.cc
+++ b/rtengine/filmnegativeproc.cc
@@ -151,9 +151,9 @@ bool rtengine::RawImageSource::getFilmNegativeExponents(Coord2D spotA, Coord2D s
     // compared to the ratio in the reference channel (green)
     for (int ch = 0; ch < 3; ++ch) {
         if (ch == 1) {
-            newExps[ch] = 2.f;  // Green is the reference channel
+            newExps[ch] = 1.f;  // Green is the reference channel
         } else {
-            newExps[ch] = CLAMP(2.f * logBase(clearVals[ch] / denseVals[ch], denseGreenRatio), 0.3f, 6.f);
+            newExps[ch] = CLAMP(logBase(clearVals[ch] / denseVals[ch], denseGreenRatio), 0.3f, 6.f);
         }
     }
 
diff --git a/rtgui/filmnegative.cc b/rtgui/filmnegative.cc
index 36f2e7c34..d84c1bd0a 100644
--- a/rtgui/filmnegative.cc
+++ b/rtgui/filmnegative.cc
@@ -273,11 +273,12 @@ bool FilmNegative::button1Pressed(int modifierKey)
             std::array<float, 3> newExps;
             if (fnp->getFilmNegativeExponents(refSpotCoords[0], refSpotCoords[1], newExps)) {
                 disableListener();
-                redExp->setValue(newExps[0]);
-                greenExp->setValue(newExps[1]);
-                blueExp->setValue(newExps[2]);
-                redRatio = redExp->getValue() / greenExp->getValue();
-                blueRatio = blueExp->getValue() / greenExp->getValue();
+                // Leaving green exponent unchanged, setting red and blue exponents based on
+                // the ratios between newly calculated exponents.
+                redRatio = newExps[0] / newExps[1];
+                blueRatio = newExps[2] / newExps[1];
+                redExp->setValue(greenExp->getValue() * redRatio);
+                blueExp->setValue(greenExp->getValue() * blueRatio);
                 enableListener();
 
                 if (listener && getEnabled()) {