Someone mentioned a paraccor. Peter is going to fit a SIPS (Starlight Integrated Paracorr System for Coma Correction).
If you are not familiar with these, I quote from Starlight Instruments (and i have no affiliation to this company):
"Starlight Instruments in conjunction with TeleVue is proud to introduce the last word in coma correction for Dobsonian telescopes. We call it the Starlight Integrated Paracorr System or SIPS for short, referred hereafter as SIPS. SIPS is unique in that it integrates the first class optics of the TeleVue Paracorr - Type 2 Coma Corrector with our state of the art, finely crafted FTF2015BCR focuser."
http://starlightinstruments.com/stor...&product_id=50