Atoche

unless she get's lots of practice before the trip with the 6D - the results she get's with the more familiar 5D and 7D (I am sure she will take both) are likely to be better than with a new ...

For me: 1.  I remember ISO, just as much as I remember shutter speed and f/stop. 2.  I set ISO for a session, then leave the same for all shots that session, to make post processing easier. Frankly ...

Since this is the crop forum... On my 7D, if I were to "walk about", I would have the 24mmL II 1.4 mounted.

I agree with everything Don has added, and I enjoy the color cast modifications that he made... although I think the shot it still off, let me explain. To my eye, the problem with the photograph ...

To my eyes, the bottom photo has more contrast, but is not "darker" or "underexposed"... what does the histogram show for each?

what type of metering are you using? (spot, center, ect)...

canon refurbished site has 6D body for $1350.  This occasionally dips to $1050 (as it did a couple months ago). I have no quam regarding canon refurbished.  To me they are like new and operate as such.

you seem to be describing effects of diffraction, but odd for me that it would occur at such a wide aperature and such a short distance. I am curious to hear and learn, hopefully an experienced ...