Digital photography

Blimey, are 5Ds normally that cheap?

Very tempting, but for astrophotography, I'd not be using all that much of the full-sized sensor as my optics don't give a big enough flat field.

And the 600D seems to have the capacity to film at a high frame rate on a cropped section of its sensor, ideal for planets or the ISS. Perhaps my criteria are a bit specialised.

And another thing, I have and EF-S lens as well as EF lenses.

Would the 5d be no good at planets? Serious question I'm thinking of buying a telescope and already have a 5d.