EF focal reducer?

I recently did some astrophotography with a friends 10" SCT telescope, and he had an f/6.3 focal reducer for his 2000mm f/10 scope, which increased the field of view by almost 40%, flattened the field and increased the light by a factor of 3. I was wondering if such a thing exists for Canon EF lenses, or if it is even possible, like the reverse of a 1.4x extender that could help reduce the x-factor.