The focuser might be struggling to stay straight and the vignetting seems excessive, but looking around the 'net it seems the TRF-2008 is not particularly well matched to the f/7.5 ED80. It does seem to work very well with some small scopes.
http://www.pbase.com/snowlep/reducer
https://astro.ecuadors.net/refractor...equinox-80-ed/