Why are 50mm Lens considered the standard?

Started Dec 27, 2011 | Discussions thread
sacundim Senior Member • Posts: 1,111
Because that's what Oskar Barnack had at hand

The 35mm still image format was invented by Oskar Barnack—the guy who designed the first Leica. How did he do it? Well, he took the already-existing 35mm motion picture film, doubled the frame (so that one 35mm stills frame = two adjacent 35mm motion frames), and stuck a 50mm lens in front of it because, well, that was the closest he could get to the frame diagonal (43mm) using lenses that were already being made.

A 45mm lens is closer to a true "normal" lens than 50mm. However, the 50mm focal length has stuck around since them for a variety of reasons:

  • Inertia. Camera companies aren't adventurous; they tend to keep building what has sold in the past.

  • Compatibility with older equipment. Nearly all rangefinder cameras have framelines for 50mm; nearly all rangefinder normal lenses made are also 50mm. If you make a rangefinder camera or lens that departs from this, it will not be a great match to people's older equipment.

  • SLR lenses need to leave clearance for the mirror, which means that 35mm SLR systems had flange focal distances from around 42mm to 48mm. This makes it easier to build large-aperture 50mm lenses than 45mm lenses. (The fastest 45mm SLR lenses I'm aware of are about f/2; the fastest 50mm SLR lenses are f/1.0.)

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