Why do photographed objects in the distance appear smaller than they do by naked eye?

There may be some psychological and human perception factors involved, but, fundamentally, objects in photographs are as big as you make them. That may sound a little over-simplified, but, really, it's all there is to it. If you have an image of a mountain, and you hold it in your arm and look at the real mountain in the distance right next to it, the photographed mountain may look either smaller or bigger depending on a) the size of the print and b) how much of that print is filled by the mountain.

If the mountain is too small, there are basically three ways you can adjust this.

First, you can of course get bigger paper and print bigger. Eventually, your printed mountain will look bigger than the distant one.

But if you're starting from a mountain which only fills a small percentage of the frame, that might be a very large piece of paper with a lot of stuff you don't care about around the edges. So, second, you can crop the image and expand. This is exactly the same as making a larger print, except... don't print the parts you don't want. Then, you can have a relatively large mountain, without all that wasteful forest and sky around it.

But, your camera might not have captured enough detail for that mountain to look good cropped. You can improve this with a better camera, higher quality lenses, using a tripod, shooting on a day with less haze, and more, but there's also an easy first step — instead of cropping to get a mountain that fills the frame, do it optically. So, third, use a lens with a narrow field of view to make the mountain fill more of your camera's sensor.

We call a lens with a narrow field of view a "long" lens — or, often, "telephoto", although this is not technically correct. A lens with a wide field of view is usually just called "wide" (although you'll hear "short", too). And, a lens in between is called "normal" — and that's partly because these lenses tend to give a field of view which roughly corresponds to human vision when printed about 8×10 and held at a comfortable viewing distance. On a 35mm film camera or a full-frame DSLR, this is around 43mm, give or take — a number corresponding to the diagonal of the sensor, so convert as appropriate for other sensor sizes.

So, to recap, yes, it absolutely has to do with field of view, which corresponds to "zoom" — or at least to focal length. The exact magic number varies based on print size, but overall, match your lens focal length and print size appropriately, and you can make that mountain either bigger or smaller.

For more on the technical details behind this, see

• What is "angle of view" in photography?
• How do zoom, magnification, and focal length relate?
• Why does a 50mm lens appear to give a human perspective, rather than a normal lens?
• What is the difference between a telephoto lens and a zoom lens?

It's because human eyes has curved hemisphere retina while the camera today are still using plain flat sensor. Curved hemisphere retina would make faraway objects appear larger while retains a wide field of view.

Until the technology advanced that we could put curved sensor in camera, the only way to simulate human eyes is to use long focal length, for example 70mm on full frame, while sacrificing wide field of view.

Flat sensor would not make far away objects looks smaller, but make size ratio of a far away object to a close object smaller than you see. If you test shoot a long bridge from one end, you would see that slope grade is much higher than if appears in your eye.

You need a next generation spherical sensor in camera to mimic what you see in your eyes.

Sony has developed a spherical sensor 3 years ago but never put it into consumer product. It would still be a long way to go to have a spherical sensor fully mimicking a human eye.