Focusing tests with the Paracorr and my 200mm / F6 Newtonian.
The Televue recommended spacing between the Paracorr and the imaging chip is 55+/-4mm, however
this does not appear to ensure that good focus is achieved.
Image A2 shows elongation of the stars in the corner of an STL-11000M when focused on a star in the centre (using FocusMax) with a Paracorr / chip distance of 54.9mm (0.375" + 0.25" spacers + STL adapter).
Images B1/B2 have the focus adjusted to make the corner field stars rounder, but this has resulted in the centre field stars becoming softer.
Images C1/C2 have been taken with a Paracorr / chip distance of 58.1mm (0.375" + 0.50" spacers + STL adapter) using FocusMax on a centre star. This is a vast improvement, with excellent focus in the corners.