Marco, no there isn't, unless the grain focuser projects the image onto a piece of ground glass. Even then you still have to adjust the eyepiece so you see a clear image.

As you get older, the eye loses it's ability to switch focus points quickly, then you will find the grain focuser becoming more accurate. or depending on your point of view. Years ago, Zeiss made a special focusing telescope so their (mostly younger) technicians could accurately align microscope camera focusing units that used an aerial image in the same way a grain focuser does.