I will be making the very expensive leap from 4x5 to digital for my architectural work, and I have a newbie question. The sensor on the Aptus Leaf ii is 40.3mm x 53.7mm, or a diagonal of about 6.7cm, which is 41% of the diagonal of 4x5 film (10.2cm x 12.7cm). So to get the same width of image that I now get with a 65mm Grandagon, I would need to find a 26mm digital lens (=41% x 65mm). The widest digital lens for this format seems to be the 35mm digitar, which I reckon to be equivalent to 85mm in a 4x5 format. Yet people seem to be taking ultrawide pictures in digital. My calculations are evidently very wrong, but I can't figure out how. What's wrong with this picture?