Converted from roc to curvature

lib/Petzval/Optics/RTM.hs

@@ -40,10 +40,10 @@ systemRTM els = foldl1 (flip (!*!)) . map elementRTM $ els
 
 -- | Compute the refractive part of the RTM for an element
 refractionRTM :: (Fractional a, Mode a, Scalar a ~ Double) => Element BakedIOR a -> M22 a
-refractionRTM  (Surface{_thickness, _outsideRadius, _roc, _material=BakedIOR n1 n2}) =
+refractionRTM  (Surface{_thickness, _outsideRadius, _curvature, _material=BakedIOR n1 n2}) =
   let ior' = auto (n1 / n2)
   in V2 (V2 1 0)
-     (V2 ((ior' - fromIntegral 1) / _roc) ior')
+     (V2 ((ior' - fromIntegral 1) * _curvature) ior')
 refractionRTM Stop{} = V2 (V2 1 0) (V2 0 1)
 
 -- | Compute the part of the RTM that represents the thickness of the element