there are a few apertures down that train that could be limiting the illumination at the corners with an f4 light cone. However, I think that 30% reduction should still be quite manageable with flat fielding - after doing this, the main effect will be a slight drop in SNR in the corners and maybe a bit of extra diffraction around bright stars - but so what? All it means is that you have an 8.5 inch scope in the corners and a 10 inch one in the centre of the field. Even the super scope designers accept significant vignetting
http://planewave.com/wp-content/uplo...-spot-size.pdf
the RCC1 is the only CC I know of that will accommodate that length of image train.