diff --git a/src/App.jsx b/src/App.jsx
index 59e571e..8262826 100644
--- a/src/App.jsx
+++ b/src/App.jsx
@@ -174,17 +174,20 @@ const PreviewPanel = ({ lensCurves, previewDistanceMeters }) => {
     }
 
     const blurMm = stat?.blurMm ?? 0;
+    const blurPercent = stat?.blurPercentOfDiagonal ??
+      ((curve.sensor?.diagonal ?? 0) > 0 ? (blurMm / curve.sensor.diagonal) * 100 : 0);
 
     return {
       lens: curve.lens,
       blurMm,
+      blurPercent,
       sensorDiagonal: curve.sensor?.diagonal ?? 1,
       colorIndex: curve.colorIndex,
     };
   });
 
-  const maxBlurMm = previewItems.reduce((maxValue, item) => Math.max(maxValue, item.blurMm), 0);
-  const denominator = maxBlurMm > 0 ? maxBlurMm : 1;
+  const maxBlurPercent = previewItems.reduce((maxValue, item) => Math.max(maxValue, item.blurPercent), 0);
+  const denominator = maxBlurPercent > 0 ? maxBlurPercent : 1;
   const distanceLabel = Number.isFinite(previewDistanceMeters)
     ? `${formatNumber(previewDistanceMeters, previewDistanceMeters >= 10 ? 0 : 1)} m`
     : '∞';
@@ -200,7 +203,7 @@ const PreviewPanel = ({ lensCurves, previewDistanceMeters }) => {
       ) : (
         <div className="flex flex-wrap justify-center gap-4">
           {previewItems.map((item) => {
-            const normalized = Math.min(item.blurMm / denominator, 1);
+            const normalized = Math.min(item.blurPercent / denominator, 1);
             const diameter = Math.max(18, 30 + normalized * 70);
             const paletteColor = COLOR_PALETTE[item.colorIndex % COLOR_PALETTE.length];
 
@@ -221,7 +224,7 @@ const PreviewPanel = ({ lensCurves, previewDistanceMeters }) => {
                 <div className="text-xs text-slate-200">
                   <div className="font-medium text-slate-100">{item.lens.name}</div>
                   <div className="text-[10px] uppercase tracking-wide text-slate-500">
-                    Blur {formatNumber(item.blurMm, 2)} mm
+                    Blur {formatNumber(item.blurPercent, 2)}% diag
                   </div>
                 </div>
               </div>
diff --git a/src/utils/optics.js b/src/utils/optics.js
index daa087a..77667cd 100644
--- a/src/utils/optics.js
+++ b/src/utils/optics.js
@@ -83,13 +83,20 @@ export const calculateBlurCircle = ({ focalLengthMm, aperture, subjectDistanceM,
   const safeAperture = coercePositiveNumber(aperture, 1);
   const f = focalLengthMm;
   const u = metersToMillimeters(coercePositiveNumber(subjectDistanceM, 0.5));
-  const s = metersToMillimeters(coercePositiveNumber(sceneDistanceM, 0.51));
 
-  if (Math.abs(s - u) < 1e-6) {
+  if (Math.abs(u - f) < 1e-6) {
     return 0;
   }
 
-  if (Math.abs(u - f) < 1e-6) {
+  if (!Number.isFinite(sceneDistanceM)) {
+    const denominator = safeAperture * (u - f);
+    return Math.abs((f ** 2) / denominator);
+  }
+
+  const sceneMeters = Math.max(sceneDistanceM, 0.2);
+  const s = metersToMillimeters(sceneMeters);
+
+  if (Math.abs(s - u) < 1e-6) {
     return 0;
   }
 
@@ -197,7 +204,7 @@ export const buildStatsAtCheckpoints = ({
         sceneDistanceM: Infinity,
       });
     } else {
-      sceneDistance = safeSubjectDistance + separation;
+      sceneDistance = Math.max(safeSubjectDistance + separation, 0.2);
       blurMm = calculateBlurCircle({
         focalLengthMm: lens.focalLength,
         aperture,