REF make this clearer

ngmix/prepsfmom.py

@@ -402,7 +402,7 @@ def _compute_cen_phase_shift(cen_row, cen_col, dim, msk=None):
     If you feed the centroid of a profile, then this factor times the raw FFT
     of that profile will result in an FFT centered at the profile.
     """
-    f = fft.fftfreq(dim) * (2.0 * np.pi)
+    f = fft.fftfreq(dim)
     pxy = _compute_cen_phase_shift_numba(f, cen_row, cen_col)
 
     if msk is not None:
@@ -416,8 +416,8 @@ def _compute_cen_phase_shift_numba(f, cen_row, cen_col):
     # this reshaping makes sure the arrays broadcast nicely into a grid
     fx = f.reshape(1, -1)
     fy = f.reshape(-1, 1)
-    kcen_x = fx*cen_col
-    kcen_y = fy*cen_row
+    kcen_x = fx * (2.0 * np.pi * cen_col)
+    kcen_y = fy * (2.0 * np.pi * cen_row)
     px = np.cos(kcen_x) + 1j*np.sin(kcen_x)
     py = np.cos(kcen_y) + 1j*np.sin(kcen_y)
     pxy = px * py