Rule of thirds

20droger wrote in post #5984382
I just double checked, and my drawing is correct (see page 17 of the 5D manual).

I would guess that the focusing system is exactly the same as that used on the 20D, but since the sensor is larger....

But hey, the 5D is a great camera. Those who own them seem to love them.

20droger wrote in post #5973147
This depends upon what you mean by a level horizon.

If you mean that the picture should really be level and the horizon falls where it may, then use a level. They make them for your hot shoe. This is, in fact, lveling an artificial horizon, something done with many scientific instruments.

If you mean the horizon should appear level in the picture, whether or not it is level in reality, then make it "level" in your viewfinder.

And, the EF-D focus screen for the EOS-40D does not divide the image into thirds, so it is of limited use for Rule of Thirds framing. There is a picture of it on page 162 of the manual.

Katz-Eye Optics makes a split-prism focusing screen with Rule of Third grid lines for the 40D. Look here and here. This screen has the advantage of the split prism as well, which really helps with manual focusing.