Photographs are rectangular. Historically, this makes sense; when photography was first invented, it was the film (or rather, photographic plates) that cost the most money versus, say, the lens, and obviously one makes the best use of the raw material of plates by cutting it into rectangles, and later the lengthly rolls of plastic film were put to best use by partitioning it into rectangles. (Hexagons could potentially work for no wastage, but this would be far more awkward, especially when it came time to put them in a roll.)
Digital cameras don’t use plates or film any more, but reusable sensors. A single sensor is reused for many thousands of photos, and so there is no reason to efficiently partition a physical medium into many subparts as there is with film.
Lenses are circular, and correspondingly image degradation (whether vignetting or other distortion) increases roughly as the distance from some center on the photographic plane. If we suppose there’s some maximum distance beyond which one cannot get a good image, the “useful” area of a photographic plane is circular. To accomodate rectangular film without wasting any of this film, whatever portion of the circle we use is a rectangle inscribed in this useful circle, meaning we are wasting at least (1-2/π) ≈ 36% of the useful circle, and that’s only if the rectangle is a square. With my own camera’s 2:3 aspect ratio, that’s about 41% wastage. (As a practical matter, it is more like 63% or so for an EF lens, I think, since it’s a crop sensor; that’s astonishing waste.) As megapixel sensor density continues to increase, we shall feel the cost of the corresponding lens wastage keenly, since the amount of meaningful detail sensors can gather begins to exceed the capabilities of all but very expensive lenses.
So, now we come to my point: digital cameras have obviated film wastage, but the rectangular shape inherited from film cameras continues to waste lens resolution. Clearly this is wrong. It is time to revisit the concept of the “rectangular” photo, to literally think outside the box. Rather than having rectangular digital sensors, let us have circular ones, and spread out that sensor resolution to cover all of the useful circle of the photographic plane.
Obviously for many applications one will still want rectangular photos, but if you wish to subset and crop your photos to be rectangular, that will be your choice. In the present rectangular paradigm, one has no choice at all.
This “radial” mode of photography would have many advantages.
The primary advantage is that when you buy a lens, you get to use all of it, not just about half of it. We pay good money for the glass only to ignore a sizable chunk of it.
There are some practical cost reasons why one could not make a photographic plane cover the entire useful field. In such a case, even if your image sensor remains the same size but has been reformed into a circle, you have given up the lower quality corners for real estate much closer to the lens center, which presumably suffers from less distortion.
Second, a photograph is more or less identical no matter the orientation of the camera. There’s no need to think about whether to photograph a subject landscape or portrait, nor even to be sure you’re keeping the horizon level. These would be details left to post processing, and totally irrelevant considerations at the time the photo is actually taken. This frees up one’s attention for other matters.
Third, lots of subjects benefit stylistically from being photographed in a circle, right up to the edge of vignetting and distortion – typical shots of faces, flowers, birds not in flight, and lengthy roads winding into the distance come to mind right off the bat – which is currently an effect one has to do with filters or post processing.