That's correct.
f ratio = focal length / aperture.
eg. C8 = 2000mm focal length, 200mm aperture, f ratio = 2000/200 = f10
This is considered 'slow' photographically.
Put a f6.3 focal reducer on the C8 and you get 200mm aperture and f = 1260mm, f ratio = f6.3.
(Note I've rounded the numbers for simplicity; C8 aperture is 8 inches which equates to 203.2mm and f.l. = 80 inches which = 2032mm)
A Newtonian of the same aperture, 200mm has typically a focal length of 1200mm, ie. f ratio = 1200/200 = f6.
A Barlow, Powermate or tele-extender increase focal length and therefore f ratio for a given aperture.
A focal reducer decreases focal length and therefore f ratio for a given aperture.
See also
http://www.televue.com/engine/page.asp?ID=237 for other methods of changing the effective focal length of a system particularly for imaging.