I usually run my camera in A mode. That means its in aperture priority - I set the aperture, the camera sets the shutter speed. The only other two options I use are S for shutter priority - I set the shutter speed, such as for sports, and the camera adjusts aperture and ISO accordingly(*) - and M for full manual; then I usually disable Auto ISO, too. So in this situation I would have used f/5.6 at most. Nothing is in close focus, I dont want shallow DoF, and there is plenty of light - so I would have just stopped down to f/5.6 to get maximum sharpness out of my lens. Now you're using a cheap kitlens, so the maximum sharpness would probably be rather at f/8 or f/11. Anyway, with f5.6, ISO 100 and 1/800 sec it would have been the exact same overall exposure, and I would have gotten the best possible data to work with. Thats really how easy it is to set the optimal settings for your camera in practice. Set it to aperture priority to control depth of field, which is usually what you want, set it to shutter priority if you need to control time instead, and set it to full manual if you have the time for it or the light situation is especially complex. (*) Actually Auto-ISO, not aperture or shutter priority, fixes the ISO if there isnt enough light to work with. One can also disable that and set the ISO explicitly. He was joking. Of course Canon has no noise issue at ISO 400. Not even if you use really old crop sensor cameras. Thats not refering to a 600D.