diff --git a/unfish_gopro_8-7_wide_hypersmooth-off.glsl b/unfish_gopro_8-7_wide_hypersmooth-off.glsl
index a89ddb0..66fcf61 100644
--- a/unfish_gopro_8-7_wide_hypersmooth-off.glsl
+++ b/unfish_gopro_8-7_wide_hypersmooth-off.glsl
@@ -1,5 +1,6 @@
-// Adapted from https://github.com/duducosmos/defisheye
-// (then resize to 1568x1080)
+// RozK
+// Adapted from https://github.com/duducosmos/defisheye,
+// itself based on http://www.fmwconcepts.com/imagemagick/defisheye/index.php
 
 #extension GL_ARB_texture_rectangle: enable
 
@@ -12,15 +13,17 @@ uniform float pts;
 const vec2 half_pixel = vec2(0.5, 0.5);
 const float pi = 3.1415927;
 
-const float input_fov = 150.0 * pi / 720.0;
-const float output_fov = 116.0 * pi / 360.0;
+const float input_fov = 156.0;
+const float output_fov = 120.0;
 
 vec2 unfish(vec2 coord) {
-    vec2 center = myResolution * 0.5;
-    vec2 pos = coord - center;
-    float rd = length(pos);
     float diameter = sqrt(dot(myResolution, myResolution));
-    return center + pos * ((diameter / (2.0 * sin(input_fov))) * sin(atan(rd / (diameter / (2.0 * tan(output_fov)))) * 0.5) / rd);
+    vec2 center = myResolution * 0.5;
+    vec2 position = coord - center;
+    float input_distance = length(position);
+    float input_foc = diameter * 180.0 / (input_fov * pi);
+    float output_foc = diameter / (2.0 * tan(output_fov * pi / 360.0));
+    return center + position * (input_foc * atan(input_distance / output_foc) / input_distance);
 }
 
 void main() {