Why is the 50mm camera lens considered closest to human vision when the average human eye image focal length is actually much smaller at 22mm?
In: 221
Because when you look at a photo you don’t hold it directly up to your eye, and it doesn’t fill your field of view.
Think of a long lens image as just being a wide angle image cropped in and blown up. So a 50mm image (on a full size sensor) looks good when it fills the same amount of your vision as the same part of a wide angle image that would fill your vision.
Because the standard film diagonal size is 50 mm. The retina is much smaller than that so a smaller focal length gives a similar field of view.
Actually the eye has a much wider field of view than a standard lens but much of that is peripheral vision. To some extent the standard lens length is an arbitrary choice that has a simple formula (equal to film diagonal) and looks to us to be in between what we see as wide angle and telephoto lenses.
It’s about the optics proportions.
Its the ratio between lens distance and sensor width.
A 50mm on a full frame sensor/film
A 35mm for a Aps-c size sensor
A 25mm for a half frame (Olympus uses them a lot)
And the human eye.
They all have the same distance/size ratio.
What it gives:
If you move the lens more distant from sensor, you zoom in more giving the picture a “flat-ish” feeling
Shorter lens distances gives the picture a fish eye / curved feeling to the picture.
The 50mm on a full frame gives the exact same curvature our eyes do, so that feels natural and perfect.
Edited for clarity.
It’s about image distortion and getting to the focal length to sensor size ratio which eliminated the slight fisheye curve you get at wider focal lengths.
The focal length “most like the human eye” is a difficult thing to arrive at objectively because there are some trade-offs involved, and you could debate the weight each factor should be given.
“Most likely to let our customers bring home good shots of the scenes they want to shoot” settles the debate by letting the customer say “this is most like the human eye *for me*.
It’s not like all that stuff about field of view doesn’t matter; that’s what consumers were subconsciously assessing when they were taking photos. But ultimately, 50mm became the standard because the camera companies wanted to maximise sales, and people could use it to take a photo of a friend, or of their family standing in front of Disneyland.
Its only estimated that a 50mm is close to a human eye on a 35mm sensor. If using a smaller sensor, say a APS-C sized one, you’d need about a 35mm lens to get the same focal length. If you use a large format camera, you’d need something like an 80mm lens for the same results.
Its not about the specifics of the lens in comparison to the eye. Its about what the internal optics of the lens, and the end results once the light hits the sensor. All of the optics on a particular focal length gives some sort of compression to whatever its seeing. Telephoto lenses, like anything over 100mm will compress things so objects in the distance will appear closer to you, and flattened out, conversely a wider angle lens like a 25mm will make things appear further away and you also start to get distortion due to the angle of the lens.
A 50mm equivalent lens is closer to a human eye because thats about what kind of compression our eyes see, give or take. You don’t get the flattening out or distortion of other focal lengths.
Let’s say you’re photographing a human subject standing a couple of meters in front of a textured background. You use three lenses, a telephoto, a 50mm and a wide angle. For every different camera lens the photographer moves further/closer to the subject so that in every photo the subject is the same size. Will the three photographs look the same? No, they will not!
Imagine projecting a cone from the front of every camera lens, this is the field of view. The telephoto lens has a thin cone, the wide angle has a wide cone. If you size the subject to take say 1/3 of the cone, with a wider angle lens things that are closer/further than the subject will be more “compressed” into the photo which is how a wide angle fits more in. This is known as perspective.
A 50mm lens *on a 35mm camera* (or equivalent dlsr *with the same focal plane distance*) happens to have a similar perspective to the human eye. The human eye has a different focal length, but has a different lens to focal plane distance, and the ratio of these gives the same field of view (approx) as a 50mm lens.
In addition to the other answers here, 50mm is one of the most commonly used focal lengths in all of photography history. This means that we are very very familiar with how it looks and humans usually prefer things they’ve seen before, the more the better.
I think you can make an easy comparison yourself. Look at something and then without looking away look through the viewfinder (not the monitor on digital cameras) of a camera with a 50mm lens (without a crop factor in camera). What you will most likely find, is that things will have approximately the same size, whether you look through the lens or not. Yes, you see less of the world, but the relative dimensions and the accompanying (lack of) distortions are about the same.
Not an optician, but I would suspect the combination of stereo vision means more than the focal length of an individual eye.
Latest Answers