Much to the surprise of many Canon fans, Canon released a new version of the Canon 20D today, the 20Da. The camera models are identical except that the ‘a’ version has the hot-mirror removed. So far the unit is a Japan only release, but I’d expect it to be available world wide soon.
Why remove the hot mirror? Well, the hot mirror is a infra-red filter glass covering the camera’s sensor. Once removed it enables astrophotography enthusiasts to capture vibrant star field pictures at extremely long exposures. The ‘a’ model is also a great feature for Infrared photography. In addition, the 20Da has a Tran missive mirror which enables live focusing on the LCD monitor.
If you are not concerned with astrophotography I’d recommend staying with the 20D normal version unless you want to go out and purchase filters for all of your lenses.