Well, it is confusing.
Originally Posted by SMBooth
From going back and looking at what you have posted, it appears that you have been looking for a lens with the largest possible image circle for a given focal length. For a camera that does not have movements, that is not necessary. Any lens in a given focal length that has adequate coverage, a large enough image circle to cover the diagonal dimension of the film, will be usable in your camera. The larger image circle of a lens with greater coverage is not usable beyond what can be captured on your film, if you do not have or need movements.
Also, I think there is a tendency, when a lens is chosen for a panoramic format, to not be aware of how much the added width of the format, by itself, will effect the increase in subject width desired without the need to go to a shorter lens. In fact, how the use of a lens that, in a non-panoramic format, was needed to increase subject width results in overkill, so to speak, with the greater aspect ratio of a panoramic format. Isnít that the advantage of the panoramic format, that you get the increased horizontal field of view at the same or larger image size without an increase in the vertical field of view that just using a shorter lens would give you? In other words, more of the width of the subject at the same level of detail and without the added sky and foreground in an image of a city skyline or a range of mountains in a landscape, for example? That was the reason for my comment about considering the use of a lens with a focal length longer than 90mm. However, if you have tried it and like the 90mm, then that is what you ought to use. In any event, with no movements, any image circle of about 180mm will suffice, no matter what focal length you choose.
And, by the way, larger maximum aperture size aggravates the problem of exposure fall off with a given lens. In fact, using a smaller aperture will reduce or, even, eliminate most of the problem and the manufacturer will generally state that getting the maximum benefit from the use of a centerfilter will require stopping down to some smaller than maximum aperture for the lens for which it is intended.