[rplst8]

> With modern materials and good technique, 8x-11x is feasible, but starting to push it at the edges; I have printed 13x17s off 35mm but I would not want to push it much larger.

Many pros push 35mm to billboard sizes. The size of the print doesn't matter. It's the viewing distance.

[HankB99]

Not a pro here, but the greater the distance, the better my pictures look. ;) Back to the subject at hand, it is a little surprising to me that a format closer to square didn't catch on at some point. I suppose that the image quality of the image deteriorates more toward the edge of a circle around the center point. The format that gets the most out of a circle of acceptable quality is a square. As the shape becomes more oblong, more of that 'acceptable quality area' falls outside the image. Perhaps this is one reason that larger formats are closer to square than 35mm.

[sjwright]

Well to be pedantic, the format that gets the most out of a circle of acceptable quality is a circle, not a square.

[HankB99]

Point taken. That makes me curious if any cameras were ever produced in that format. I would suspect that circular format photography might be used in astronomy where every last bit of the image is valuable.

[sjwright]

Yo’re right though, a square is certainly the rectangle of largest area from a circular lens.

If there was a need to maximize the capture for technical reasons I imagine it would be easier to just oversize the film or sensor and trim the corners.

[gchpaco]

There's a number of fisheyes that produce circular images on rectangular film (obviously, not using the entirety of the film surface).