I have a 500mm Vivitar f6.3 (72mm aperture) that I have used "piggyback" on my scope for shots of M31, M42, M45 and other large scale, wide field shots. It works just fine but I must say that focusing it can be a bear. If it wasn't for the FWHM function in the Frame and Focus module of Backyard EOS I'm not sure I could get it focused properly with any regularity. As for planets, just not enough magnification. You are better off using prime focus or eyepiece projection with your telescope. Better yet use one of the relatively inexpensive webcam style video cameras like the Celestron NexImage V or the Orion Star Shoot Solar System Color Imager IV. Importing their .AVI videos into Registax or Autostakkert is simple and easy with a very high success ratio for really good images.
Denham Springs, Louisiana USA
"Second star to the right - Then straight on until morning!" - Peter Pan
Celestron CPC1100GPS (XLT) - 279mm aperature, 2800mm Focal length. (f10) Celestron Ultima LX (70deg AFOV) Eyepieces 32mm thru 5mm, Canon EOS Rebel T2i DSLR, Backyard EOS imaging software, Orion Star Shoot Planetary Imager IV, Celestron Skymaster 15x70 binoculars