I have never tried it with a smaller scope, and am not sure about adapters for refractors, but focusing with the C-90 was difficult, but in good light, was very sharp. The bokoh on mirror catropic lenses is a bit strange, because of the center mirror. My tripod head back then was not very good, and no IS, so mirror lock up is essential. Vibration at 1000mm is quite pronounced, and any technique for stopping vibration would be advised. I used to use the lean into the lens/tripod trick, but adding a hanging wieght the tripod would seem like a good idea. BTW, the T-mount/adapter was not expensive, and the C-90 is apears to be no longer made, but the C5 would be an excellent choice, but not cheap. However, any of these scopes are a LOT cheaper than a Canon 600mm (or the 1200mm).