35mm cameras are still stuck in the 3:2 aspect ratio, even after the SLR mirror box and film limitations are gone. 3:2 has not been the most pleasing aspect ratio for art, which is traditionally 4:3 and even squarer. And 4:3 uses the lens circle area more efficiently. How did 3:2 become the 35mm camera standard?

What should have happened, now that film and the SLR mirror box is gone: oversized sensors. I’ve long argued that digital cameras should have oversized sensors, so what the lens sees can be captured by the camera in other aspect ratios like 4:3 and 16:9.

Panasonic’s multi-aspect ratio sensor never made it to full frame, sadly, and has almost been completely abandoned. I mention the medium format GFX solution below the article.

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What historic reasons are there for common aspect ratios?

Thomas Edison’s lab chose a 4:3 ratio for silent film, and it became the standard. … there’s precedent in visual arts — analysis of several different datasets generally shows that the most common aspect ratio for paintings is something close to 4:3, with 5:4 also popular. …

Oskar Barnack of Leitz invented a small camera using cinema film rolls, and chose to use a double frame — and a double-4:3 frame is 4:6 — which is to say, 3:2 when you turn it 90°.

(Beware when searching for more on this; there’s an oft-repeated article out there full of unwarranted golden-ratio mysticism. Not only is 3:2 not even close to the golden ratio, but, as noted under 1:1 below, historically artists have shown a preference for more-square formats which are even further from the golden ratio.) Japanese camera makers Nikon and Minolta used a 4:3 format in their first 35mm film cameras, but then switched to 3:2 along with everyone else — possibly for political reasons, but possibly just for convenience. …

16:9 is the standard for HDTV, of course, and it was simply selected as a compromise format by the committee… it’s not ideal for either the classic ratio [4:3] or common widescreen formats [more than 2:1], but sits in the middle….

Entire Article

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3:2 sits in the middle for cameras

Another reason manufacturers may have used to keep full frame stuck in 3:2:

Since still cameras are often used to shoot video now, with 16:9 being the standard ratio, it’s better to crop 16:9 from the wider 3:2 aspect ratio than 4:3.

Nikon, Canon and Sony are no longer prioritizing still photo shooters with their gear.

Exceptions: micro four thirds are smaller sensor cameras in the 4:3 ratio, and Fuji’s medium format GFX cameras are 4:3, and can use most full frame SLR lenses with an adapter in various aspect ratios; though, cropping has to be done in post, and the viewfinders aren’t optimized for shooting full frame lenses, except in 3:2.