I just saw this post as I recently got an SP and needed eyepiece correction. Here’s an update to the very helpful advice above, referencing the PDF instructions on how to modify the Nikon DK-20C currently-available eyepiece corrector. I did not file off the little “ears” as recommended in the modification instructions. I did thin the back of the DK-20C, which worked brilliantly. The little ears flex and actually help hold the corrector in place. This is a great solution, and thank you to the poster for having posted it long ago - it’s still helping people like me!