In my optical setup, I have a standard 4f setup with  plano-convex lenses with focal lenght of 300mm . After focusing it, I found out that i have a huge field curvature. To reduce this i designed a setup with two sets of planocovex lenses with focal lenght  of 600mm (to have almost the same propagation lenght of 1200mm) thereby reducing the petzval field curvature.  Eventhough the field curvature was reduced by a factor of 3, the field curvature is still signinfiact. The 3rd approach was to design custom lenses. I was working with 2 pair of lenses and was using REAR and FCUR to reduce the field curvature. When i look into the seidel graph there is no field curvature. But when i focus it using a paraxial lens, i can see there is noticable field curvature. Is there any was to reduce this further atleast lower than the half of the rayleigh length.