Hey,
Im thinking about changing my trusty old 1ds3 for 5d3. Im not a pro, so I shoot mostly for my fun, but I do love photography and printing large. I mostly shoot landscape, portraits, events and other stuff as well.
I would like to upgrade, as I miss the iso in the 1ds3 and it does get quite heavy carrying around all day 
Also the technology on the 1ds3 is already a bit dated ...(hate the low res screen) ...
If someone has both cameras, can you please compare the image quality and any pros and cons for the cameras.
Maybe for IQ, weather sealing(used the 1 this weekend in pouring rain), print quality, high iso, af,...
Thanks.
T
I had both. I'll do some simple comparisons. The 1Ds3 is a monster of a camera. To shoot shots at that high of an IQ and high of resolution beginning back then, is amazing. I think it is Canon's last real improvement in an "IQ camera." With that said, overall, I was happier with the 5D3 so I sold my 1Ds3.
The 5D3 will shoot at comparable IQ's, even at low ISO. Probably though, the IQ of the 1Ds3 is slightly better at low ISO, say 100 to 400. Beyond that the 5D3 takes over, because of it's better higher ISO performance. At ISO 1000, the 1Ds3's images began to look "pixely" and just gets worse from there.
The 1Ds3's most stunning quality was how accurate it got the skin tones, in low ISO settings of course. That is the one thing I miss. I never had to mess with skin tones in post. I don't really miss anything else about it, because now I can take the 5D3 anywhere and if I don't have a flash, I can still shoot at ISO 5000 if I had to with no worry. Again, IQ's to non-pixel peepers are probably comparable at low ISO, but increases in the 5D3 as ISO increases. I would say though, if I had to pick a winner at low ISO, the 1Ds3 would win.
There are other features, such as the AF system of the 5D3. The thing the 5D3 does not have that the 1Ds3 has is active AF point spot metering. The actual metering seemed a bit more accurate in the 1Ds3.