New to me 5Dii, have few questions

Got my new (used) 5Dii today and have a few questions about operation.

I love the fact that there is a separate focus button on the rear of the camera. How does one disable the focus operation from the shutter button? I keep reading the manual but I tink the terms I am reading aren't registering with me in terms of "off" or "disable".

Second, I am placing the ISO in auto for now, but whatever i seem to focus on, the ISO setting automatically goes to 400. Doesn't matter if I'm looking at something sunny outside or in a lit room. This doesn't change regardless of my shutter speed selection or aperature setting.

I must say, I LOVE the heft and size of the camera. I originally chose Canon over Nikon because the D3100 I held seemed small in my hands. This camera fits like a glove. Wish I could enter copyright info from the camera controls like I could wih my T3i. Oh well.

Thanks.

<edit> I think I found the shutter disable. Metering start metering/af start selection

In the custom functions section, you want the shutter button to be listed as "Start meter" or something to that effect.

custom function 4, menu 1, option 2.

Thanks guys. Did find that one.

I'm not used to the camera going to 400 ISO like that in auto ISO. I'm using my 70-200 at 2.8 and it's not only sunny outside but also snow covered, so tons of light. My old T3i would instantly go to ISO 100 in this case. Perhaps this is a function of the full frame vs the crop sensor I had? differing ages of camera?

<edit> think something is wrong because no matter the light level, auto ISO go to and stays at 400 no matter the light level.

Ok foolish me to not have done a search. Found in manual mode, the camera defaults to ISO 400 and there is no "auto" function. Amazing that a camera that sold for 30% the cost has this function standard. Go figure.

Anyway, does anyone know if Auto ISO will work if you set up your camera to use one of the custom functions (C1, C2, or C3?) Still going through the manual but its nice to find an expedited way.

For me, when I set my 5D2 to Manual - I don't expect anything to be 'auto'. In fact, I never knew until now, you could even set ISO to auto on Manual - never tried it myself.

Enjoy the 5D2 - it's a great camera.

Congrats on the 5Dii