Thanks for all the great advice. That e-book might be very useful.
I was checking focussing screens .
Am I correct there are no Canon focusing screens for the 5D Mark III.
Is it even necessary / helpful?
As far as I know, changing the focusing screen is recommended for wide aperture lenses (f < 2.8 ), so I don't think it will help with the TS-E 24mm.
Replacing the screen on the MK III is not as easy as with the II - it is not intended to be user-changeable.
Best option for focusing is live view, zoomed in, and scrolling across the image to see if the focus plane is in the right position