Ray Gralak <rgr@...>
If you want to reduce periodic error just for the fun of it,I've experimented with various levels of periodic error in my 1200GTO mount
(not only did I reduce PE but I made it artificially higher for testing by
loading an appropriate PE curve). Using a 5-second autoguider cycle just by
turning on PEM reduced FWHM by 0.15 arc-seconds when going from 3.0 arc-sec
PE to 0.5 arc-sec . The stars looked just as round in each case, but the
FWHM of the stars with PEC on were tighter.
Also, for those autoguiding through a narrowband filter with an SBIG camera,
good PEC is critical. It will allow you to increase the autoguider exposure
time to get a guide star through the narrowband filter.