Just take note though that with a +4 filter, your focusing distance is ard 25cm. And if mounted on any lens, be sure to adjust your focus distance to the minimum. This will allow you to get max magnification at any focal length.
I have a friend who uses two Hoya +4 filters stacked to take flower macros on his 18-55 kit lens. So I'm not sure if the +4 filter will be useful on your 50f1.8 lens since I believe the 50f1.8 focusing distance is pretty near.