I noticed the same thing, the shutter speed indicator in my prism finder isn't in focus either. The cause of this must be that the indicator segments aren't in the plane of the camera ground glass but located nearer to the diopter.
Originally Posted by paul ron
I haven't tried yet, but it may help to not letting the lens go all the way up on the original diopter, leaving a narrow slit to view the segments through, or even using a piece of lens with a different strength in the segments part of the field of view.
I'll give it a shot as soon as time permits.
The segments are still readable in my finder despite being a bit out of focus, but this may be dependent on the lens strength used for the diy diopter.