I just purchased an adapter from www.omextech.com. It's called the Digi-Mic Adapter (DMA-2 for my camera) and replaces the eyepiece of the microscope.
So, far, I've been very pleased. I bought the adapter, which fits microscopes with 23mm eyepieces and the 30mm sleeve to use with my stereo microscopes. Very nicely machined. Fit's perfectly in the scopes I've tested so far and has worked well with both the low-end Casio and the Canon 400D.
It's around $200; but, well worth it to me having used the lower end adapters. A LOT less hassle. LOL
I'll be trying it with a Canon S2 to replace the Casio and will post some images.