The Canon S90 point & shoot digital camera appears to be an adequate choice for digiscoping, but it's not without a minor problem. Unfortunately, Canon doesn't make an accessory adapter to bring it out to a convenient filter thread to support Swarovski's DCA or Kowa's DA1. There is a third-party adapter (37mm) made by LensMate, but it attaches to the S90 via an adhesive of some type that seems a little risky and inconvenient to me. However, the camera will mount to bracket adapters like the Swarovski UCA or Kowa DA4. Kevin Bolton has been getting stellar digiscoping results with the S90 and his Kowa 88 scope!
