Comparing Camera & Human Eyes: Zoom & Focus

[pivoxa15]

Is a camera very much like a normal (i.e. perfect vision) eye? If we wear lenses, we will like the camera be able to 'see' focused images very far away or very close which is like zooming in or out with the camera.

Some people with eye problems like myopia cannot see a focused image beyond their near point so they see a blurred image. However, I have noticed my camera never register a blurred image no matter if zoomed in or out. Why is this?

Why does a camera always register a focused real image on the film no matter how its zoomed but the human eye is subject to defects like myopia, even though the camera and eye are very much alike?

Note: I understand that the human eye is unable to zoom because it recquires multiple lenses whereas we only have one but normal eyes can focus near and close objects because our single lens is able to contract and expand.

 

[turbo]

A camera is subject to the same laws of optics that our eyes must obey. For instance, if there is a lot of light, you can "stop down" the aperture of the lens, just like our irises "stop down". This yields sharper images and a greater depth of field - objects in a much greater range of distance will appear to be in focus. If there is less light available (given the same shutter speed) the aperture of the lens and the irises in our eyes have to open wider, and the focus becomes softer, the depth of field shrinks, and any optical defects in the lens become exaggerated. Due to the shape of our eyeballs (primarily) and the shapes of our lenses, we might see better at distance or close-up, though as we age, our ability to deform our eyes' lenses decreases, and we typically lose our ability to focus on things that are very close - this is called presbyopia. A camera is easier to control, because we have not only the aperture as a variable, we can also use shutter speed. If there is sufficient light, we can use very tiny apertures and long shutter speeds to maximize the depth of field and to blur motion. This is sometimes very pretty when photographing waterfalls, etc. We could instead choose to use very short shutter speeds and large apertures to minimize the depth of field and freeze motion. This can be very effective when you want a crisp photograph of something that moves very fast, like a hummingbird. If you have more questions, fire away.

 

[billiards]

You must have a good camera, my camera quite often gives blurred images. What camera do you have?

 

[pivoxa15]

You must have a good camera, my camera quite often gives blurred images. What camera do you have?

I am talking about taking stationary photographs in ordinary situations (i.e. people being still and smiling to the camera with a stationary background).

When taking pictures of objects in motion, it becames blurred. I have an average priced camera.

 

[pivoxa15]

turbo-1, you gave lots of information there but did you answer

"Why does a camera always register a focused real image on the film no matter how its zoomed but the human eye is subject to defects like myopia, even though the camera and eye are very much alike?" What would it take for a camera to register an unfocused hence blurred photograph of a stationary object and background? A person with normal vision is able to see objects in motion without a blur that could be due to how to visual sensory system works whereas a camera only takes a single picture at a time and registers it on a film.

 

[chroot]

Put your lens close enough to an object, and try to take a picture. If you're close enough, you will exceed the camera's focus range, and your picture will indeed come out blurry.

- Warren

 

[disregardthat]

When taking pictures of objects in motion, it becames blurred. I have an average priced camera.

This is not because of the focus. It is because the camera catches the light when the object is in point A and all the way to point B. (Point A starts when the lens open, and point B ends when it closes. The camera doesn't understand that something is moving, it will 'snap' the photo as it was standing still (of course)

 

[turbo]

turbo-1, you gave lots of information there but did you answer

"Why does a camera always register a focused real image on the film no matter how its zoomed but the human eye is subject to defects like myopia, even though the camera and eye are very much alike?" What would it take for a camera to register an unfocused hence blurred photograph of a stationary object and background? A person with normal vision is able to see objects in motion without a blur that could be due to how to visual sensory system works whereas a camera only takes a single picture at a time and registers it on a film.

You're mixing problems. We see moving things relatively sharply because our eye and visual cortex is able to process information in real time. Cameras need time to integrate the light on the film or chip, so moving objects can appear blurred. Please bear in mind that our eyes have limitations, too - did you ever see a bullet speeding toward its target?

As for focus, if your camera has auto-focus, it will probably give relatively sharp images for a wide range of distances. Like Warren said, cameras have limitations, and if you exceed them (usually by trying to focus on very close objects) the camera cannot give you a clear image.

 

[pivoxa15]

You're mixing problems. We see moving things relatively sharply because our eye and visual cortex is able to process information in real time. Cameras need time to integrate the light on the film or chip, so moving objects can appear blurred. Please bear in mind that our eyes have limitations, too - did you ever see a bullet speeding toward its target?

As for focus, if your camera has auto-focus, it will probably give relatively sharp images for a wide range of distances. Like Warren said, cameras have limitations, and if you exceed them (usually by trying to focus on very close objects) the camera cannot give you a clear image.

Okay. My original question wasn't directed at photographing moving objects. The question is more about Can cameras have myopia or hyperopia? and focusing by our eyes. In other words what kind of damage must be done to a normal working camera so that it produces photographs of objects beyond a certain distance that are blurred? Or Within a certain distance becomes blurred? Hence prodce a photograph of a still moment that would be seen exactly by a person with myopia or hyperopia.

I have assumed the camera has auto focusing. The only buttons I usually pres before taking a photo are the zooming ones. The focus is always sharp. Normal eyes don't have this zooming ability but it can always focus unless you have an eye problem, why? billiards, maybe your camera doesn't have auto focus.

 

[chroot]

A well-designed camera can focus at any distance between a couple inches and infinity. If the lenses are made improperly, either (or both) of these endpoints can be affected, and the camera will have a reduced focus range. If the focus mechanism is designed (or manufactured) improperly, the lenses will not be able to move far enough to achieve the designed focus range.

It's not really possible to "damage" a camera in a controlled fashion to make this happen, without removing lenses and physically changing their shape. You could also change the positions of the mechanical stops inside the focus mechanism, preventing the focus motor from moving the lens far enough to achieve focus. You could probably also reprogram the camera's microcontroller to prevent it from moving the lens far enough to achieve focus.

- Warren

 

[pivoxa15]

A well-designed camera can focus at any distance between a couple inches and infinity.

- Warren

That sounds like a normal working eye (for humans at least). Why is this (being able to focus at any distance) so both for the camera and our eyes. Is it because of the perfect combination of image distance (distance between lens and retina or film) and lens magnification? What about the change of shape of the lens? I know it happens to the human eye but what about the camera?

 

[chroot]

The lenses in a camera move to achieve focus. They're driven by a tiny motor, or, in the case of older manual-focus SLR lenses, by the photographer's hands. There are (at least) two lenses, and the distance between them determines the distance of focus.

- Warren

 

[turbo]

That sounds like a normal working eye (for humans at least). Why is this (being able to focus at any distance) so both for the camera and our eyes. Is it because of the perfect combination of image distance (distance between lens and retina or film) and lens magnification? What about the change of shape of the lens? I know it happens to the human eye but what about the camera?

What is it with this absolutism? The laws of optics prevail and our eyes and the lenses of cameras must obey them. Neither the human eye nor a camera can achieve sharp focus at all distances under all circumstances, and your generalizations to the contrary cannot alter this. Think it over before you post again.

 

[pivoxa15]

What is it with this absolutism? The laws of optics prevail and our eyes and the lenses of cameras must obey them. Neither the human eye nor a camera can achieve sharp focus at all distances under all circumstances, and your generalizations to the contrary cannot alter this. Think it over before you post again.

Good pint. I think I realize that the eye and the camera have limitations. The near point for our eyes is about 25cm. Any object within this distance registers a blurred image on the retina. What is the far point for our eyes (i.e. the distance in which beyond it cannot register a focused image)?

Cameras also have this limitation as you could take a photograph of a close object but the background looks blurred. I can remember sesing something like that somewhere, especially in motion pictures like movies and the blurred background can be made into focus by zooming in on it. This raises the question, what is the difference between zooming and focusing? It is assumed that a zoomed image is always focused or else you are in trouble. So in a camera, the first step is to focus on an object and the second step is to zoom in or out depending on your inteded magnification. However, our eyes don't have this zooming ability do we? All we can do is focus?

see http://en.wikipedia.org/wiki/Image:Zoom_prinzip.gif The paragraph
"Your eye has a fast autofocus! Try this simple experiment: Hold your hand up near your face and focus on it, and then quickly look at something past your hand in the distance. The distant item will be clear, and your hand will not be as clear. Look back at your hand. It will be clear, while out of the corner of your eye the same distant item will not be as clear. Your camera is not nearly this quick or this precise, so you often have to help it."

in http://electronics.howstuffworks.com/autofocus5.htm looks interesting.

 

[chroot]

Good pint. I think I realize that the eye and the camera have limitations. The near point for our eyes is about 25cm. Any object within this distance registers a blurred image on the retina. What is the far point for our eyes (i.e. the distance in which beyond it cannot register a focused image)?

The eye can nominally focus at infinity -- i.e., at an object at an infinite distance away. A person suffering from myopia (nearsightedness) cannot focus all the way to infinity, but can only focus to, say, 100 meters away.

Cameras also have this limitation as you could take a photograph of a close object but the background looks blurred. I can remember sesing something like that somewhere.

Of course, cameras, like eyes, can only focus a specific range of distances; this is called the depth of field, and depends on the aperture of the lens. Since you can change the aperture in a camera, you can also change its depth of field.

- Warren

 

[jtbell]

A person suffering from myopia (nearsightedness) cannot focus all the way to infinity, but can only focus to, say, 100 meters away.

I think that would be considered very mild myopia. My "far point" is about 10 cm, so my eyeglasses are diverging lenses with about 10 cm focal length. My "near point" is about 8 cm, so I also need bifocal lenses so I can read without having to switch eyeglasses.

 

[pivoxa15]

The eye can nominally focus at infinity -- i.e., at an object at an infinite distance away. A person suffering from myopia (nearsightedness) cannot focus all the way to infinity, but can only focus to, say, 100 meters away.



Of course, cameras, like eyes, can only focus a specific range of distances; this is called the depth of field, and depends on the aperture of the lens. Since you can change the aperture in a camera, you can also change its depth of field.

- Warren

Can the camera with a certain aperture focus at infinity?

 

[chroot]

A properly-designed camera can focus at any distance, regardless of aperture. For instance, a camera can put something at 10 meters in focus, regardless of aperture.

Aperture affects the range of distances that are in focus. A camera with a narrow iris (small aperture) can focus a larger range of distances than a camera with a wide-open iris (large aperture).

You may wish to learn about the so-called camera obscura, or pinhole camera, which is a sort of "optical system" with an almost vanishly small aperture. Everything (from zero distance to infinite distance) is in focus with such a tiny aperture.

- Warren

- Warren

 

[pivoxa15]

A properly-designed camera can focus at any distance, regardless of aperture. For instance, a camera can put something at 10 meters in focus, regardless of aperture.

Aperture affects the range of distances that are in focus. A camera with a narrow iris (small aperture) can focus a larger range of distances than a camera with a wide-open iris (large aperture).

If a properly-designed camera can focus at any distance, why have different apertures like narrow iris or wide-open iris? Or are you talking about zooming effects?

You may wish to learn about the so-called camera obscura, or pinhole camera, which is a sort of "optical system" with an almost vanishly small aperture. Everything (from zero distance to infinite distance) is in focus with such a tiny aperture.

if only our eyes were like that. This system dosen't have a lens so many common eye problems wouldn't happen.

 

[chroot]

If a properly-designed camera can focus at any distance, why have different apertures like narrow iris or wide-open iris? Or are you talking about zooming effects?

You don't focus on a specific distance; you focus on a range of distances. For example, a camera with a wide-open iris might be able to focus anything from, say, one meter to two meters distance. If you close the iris, but don't touch the focus, it might bring everything from half a meter to a thousand meters into focus. If you close the iris a bit more, it might bring everything from a few centimeters to infinity into focus. The aperture affects what range of distances are in focus simultaneously. Look up the so-called circle of confusion for more information on what it means to be "in focus."

- Warren

 

[jtbell]

If a properly-designed camera can focus at any distance, why have different apertures like narrow iris or wide-open iris?

As chroot noted, the range of distances that are in acceptably sharp focus depends on the diameter of the aperture. This is called depth of field.

The amount of light that reaches the camera's sensor for a particular image (what photographers call the exposure of the image) depends on the aperture (diameter) and on the length of time the shutter is open (photographers call this the shutter speed even though it's a time interval and not a "speed" as physicists define it).

You can change the exposure by changing either the aperture or the shutter speed. Various combinations give the same exposure, for example:

1/800 sec at aperture f/4
1/400 sec at f/5.6
1/200 sec at f/8
1/100 sec at f/11
1/50 sec at f/16

all deliver the same total amount of light to the sensor.

Combinations with "faster" shutter speed and larger aperture can "freeze" faster-moving objects, but have a very shallow depth of field. Combinations with "slower" shutter speed and smaller aperture are liable to "motion blur" of fast-moving objects, but have a larger depth of field. It's a fundamental tradeoff that all good photographers have to become familiar with.