Hi Darrin - welcome to IIS!
Telescopes are not, as many may think, entirely fixed in the focal ratio. The "native" focal ratio of your SN8 may be f/4, and that is a function of its focal length divided by its aperture - not mirror. If you stop-down your f/4 scope with an aperture mask you'll turn it into a "Herschelian" telescope, with a slower f/ratio. Typically, planetary refractors all have high f/ratios, such as f/13 and up.
This will give you a scope that doesn't pull as much light, and therefore doesn't capture as much atmospheric turbulence. It will be more forgiving in the focus stakes (less critical) and is generally a better planetary scope for it. Depth of field will also subsequently increase. I used to do the same with my old f/5 8" newtonian - using the supplied 2" aperture mask. If you hit a lousy spot on the primary with the small light cone (doubtful, but possible) just rotate the mask and try another spot.
Give it a go!
