The people at CKCPower will be releasing the CrystalVue LX shortly (X8). Initial test shots I have seen suggest that it may work well with many large lens cameras including the C2100 and E-100RS.
However the camera zoom range without vignetting was not clearly stated.
If it does work well, a 10X camera with 8xLX (effective 80x) may be a good alternative to a 3x camera with 20-30x spotting scope.
Not sure about quality of optics though.
When available, I'll probably purchase and I'll post a review.