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Comment by paulsmith

2 days ago

Another good rule of thumb to remember is that a 50mm lens on a 35mm sensor ("full-frame") is roughly the equivalent FOV of the human eye, i.e., what you see naturally.

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paulsmith

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weinzierl  2 days ago

I never understood that argument. By pure FOV the human eye is much wider. Of course it is not that simple, spacial resolution drops off to sides (while temporal resolution increases). This makes statements like "50 mm on 35 mm is FOV of human eye" not very meaningful.

  • fsckboy  2 days ago

    if you take a 35mm SLR with a 50mm lens and rotate it vertically (portrait) and hold the viewfinder up to one of your eyes, and leave the other eye open, your binocular vision will merge the two images with no problem/distortion, as if you were not holding a set of lenses up to one eye.

    since what you see through the viewvinder is what the taken picture will look like, it is neutral like/wrt your eyes, at the zero middle between wide angle and telephoto. (it's worth considering "who says eyes are neutral?" it's the system we are used to and our brain develops to understand)

    it's non obvious to a casual observer that the mm units chosen for the image size (the image gets focused on a 35mm rectangle (you need to know the aspect ratio)) and mm for the focal length are measuring different things, but that's why you just need to "know" that 35mm and 50mm "equal neutral". there are more things measured in mm as well, like the actual width of the primary lens which indicates how much light is gathered to be focused onto the same square.

    i'm not a photographer. i don't quite know the mm lingo for what happens when the image sensor/film is wider then 35mm, the large/full formats. the focal lengths "work" the same, but a larger image would need to be focused and that seems like it would require some larger distances within the lens system.

    • dghlsakjg  4 hours ago

      The phenomenon you describe is a function of viewfinder magnification. It so happens that many SLRs had their magnification such that it worked well at 50mm to shoot with both eyes open. There are SLRs that have different magnification so this trick doesn’t always work.

      You can get a rangefinder style camera with a viewfinder that lets you shoot with both eyes open but has a 35mm POV.

      People have a variety of theories as to why 50mm is considered the standard lens and why people say it mimics human vision. I have heard so many explanations that I am inclined to say that there’s not really much but opinion behind it. It might just be that it was the most common first lens and because it is cheap and relatively simple to make a good, fast 50mm lens.

    • namibj  1 day ago

      The large format ones get a higher FOV in degrees. IIRC if you keep absolute aperture the same and change focal length to keep FOV the same, the DOF won't perceptually change.

      Now, when you realize that there are geometric limitations to how wide an aperture can be relative to the focal length without having to stray from vaguely traditional _shapes_ of the objectives ("camera lens"), you can see that at the expense of fancier abberation corrections and of course larger/heavier glass lenses making up the larger objective, one could use a proportionally wider aperture with large format cameras.

      For example, the infamous Barry Lyndon objectives were actually "just" 0.7x teleconverted spinoffs from an originally 70mm f/1 design. https://web.archive.org/web/20090309005033/http://ogiroux.bl...

  • fvgvkujdfbllo  2 days ago

    The way I understand is that it is not FOV but zoom level. If you look through a camera with 50mm lens, the subject and background should appear same size as when viewed with naked eyes. Doesn’t matter if it is full frame or crop sensor.