A few of you have asked me for more details. I currently use the 5D (original) with a 17-40 lens, my intention was to have a serious attempt at astrophotography and therefore I was certain I was going to get the 24 L II. I also thought I could sell the 17-40 and just use the 24 L II for landscapes and astro. However, I also intend to upgrade the 5D to either the 6D or the 5D3 next year. These cameras seem to have a much better high ISO capability than my 5D and therefore the 24 L II might not be necessary for the astro work and I could 'get away with' the 24 IS (being lighter is a big plus for me). Hope you can understand my ramblings!!