I've yet to try my 5D MkII out as a tool for astrophotography largely because I've been without a notebook PC for the last year. But my attention was drawn to this
article on the excellent Christian Buil site (software
) comparing the Canon 40D, 50D, 5D, 5D Mark II cameras and, incidentally, a dedicated CCD chip, the Kodak KAF-3200ME. The Kodak chip wins hands down (no surprise there) but obviously that's very specialised kit compared to the general purpose DSLRs.
But a couple of images drew my attention as they illustrate how badly Live View can affect sensor performance when you are struggling to make best use of every photon.
Part of a RAW image taken in the dark with the 5D Mark II just after power on.................The same part after 10 minutes of LiveView display.
..............The exposure time is 300 seconds for the two situations. The dark signal increase by a factor 5 after a long LiveView session.
I think the moral here is to wait as long as you can after using Live View as a focussing aid before starting a sequence of exposures. My own previous experience with a 40D taught me that it also pays to give the sensor a chance to cool down between exposures. Pretty obvious stuff, I suppose, but it's easily forgotten in the heat
of the moment, especially when you see those clouds oiling in.