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Author Topic: Would we be able to see further if we had bigger eye-balls?  (Read 24891 times)

Offline Don_1

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Would we be able to see further if we had bigger eye-balls?
« Reply #50 on: 16/04/2009 17:51:23 »
I agree with you on the matter of diffraction, distortion, dust pollution, light pollution and all else which will prohibit clear vision over such a distance, regardless of the size of the sensor or the focal length of the lens. Your two 1mm spots on the Moon will be practically obliterated by the Airy Discs around them.

Geeze, I wish I'd never mentioned the Moon now. I was using it as an extreme example of how far the human eye can see.

The question is 'Would we be able to see further if we had bigger eye-balls?', not 'Could we see clearer (ie overcome distortion, diffraction etc.) if we had bigger eyeballs?'

I have been trying to say, you don't need a bigger eyeball to see any further, but an improved retina would make more distant objects clearer, as it does for the eagle. I don't think I have suggested that any improvement to our vision would overcome the obstacles, man made and natural, which limits *our* visual capabilities.

* Make that ANY visual capability.
« Last Edit: 16/04/2009 17:53:55 by Don_1 »
 

lyner

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Would we be able to see further if we had bigger eye-balls?
« Reply #51 on: 17/04/2009 00:25:10 »
So altogether, what do we need to take into consideration here?
Ask astronomers why they don't have reproduced the optical capabilities of an eagle's eye (or more) in a telescope with the same dimensions. It's not mostly about technological limitations, but mostly because of the diffraction limit.
With sufficient SNR, in hand, the diffraction limit isn't necessarily a limit. The Rayleigh Criterion is only a rule of thumb for conventional viewing. The real limitation comes from Mr Shannon (+edit)and this governs the amount of valid 'computer enhancement' possible.
« Last Edit: 17/04/2009 00:29:46 by sophiecentaur »
 

Offline lightarrow

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Would we be able to see further if we had bigger eye-balls?
« Reply #52 on: 17/04/2009 01:09:47 »
...
The question is 'Would we be able to see further if we had bigger eye-balls?', not 'Could we see clearer (ie overcome distortion, diffraction etc.) if we had bigger eyeballs?'
And which is the difference? To be able to discern a farther object you need a greater resolving power.
 

Offline lightarrow

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Would we be able to see further if we had bigger eye-balls?
« Reply #53 on: 17/04/2009 01:11:51 »
With sufficient SNR, in hand, the diffraction limit isn't necessarily a limit. The Rayleigh Criterion is only a rule of thumb for conventional viewing. The real limitation comes from Mr Shannon (+edit)and this governs the amount of valid 'computer enhancement' possible.
Can you explain better?
 

Offline Chemistry4me

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Would we be able to see further if we had bigger eye-balls?
« Reply #54 on: 17/04/2009 01:12:52 »
...
The question is 'Would we be able to see further if we had bigger eye-balls?', not 'Could we see clearer (ie overcome distortion, diffraction etc.) if we had bigger eyeballs?'
And which is the difference? To be able to discern a farther object you need a greater resolving power.

Touché.
 

Offline Don_1

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Would we be able to see further if we had bigger eye-balls?
« Reply #55 on: 17/04/2009 09:52:45 »
...
The question is 'Would we be able to see further if we had bigger eye-balls?', not 'Could we see clearer (ie overcome distortion, diffraction etc.) if we had bigger eyeballs?'
And which is the difference? To be able to discern a farther object you need a greater resolving power.

Precisely the point I have been making! Greater resolving power requires an improved retina, which does not necessarily require a bigger eyeball, as the eagle's eye demonstrates.

When I suggested that 386,242.5 megapixels would be required to see your two 1mm spots on the moon, this really was 'tongue in cheek'. There really is no way any eye or camera could pick out such fine detail over such a great distance and for a retina to have this number of megapixels (cones) our eyeball would probably need to be the size of our head.

I was assuming the question was 'relative to our current capability', not 'to an infinitesimal degree'. Relativity must be applied to this argument; the bigger eyeball must be capable of being housed in our existing head, not a head 10x bigger.

...
The question is 'Would we be able to see further if we had bigger eye-balls?', not 'Could we see clearer (ie overcome distortion, diffraction etc.) if we had bigger eyeballs?'
And which is the difference? ....

I can 'see' a bus at 100m; I can read it's route number at 100m; so can an eagle (if it could read). I can 'see' a bus at 250m, but I cannot read it's route number at that distance, an eagle can. I can 'see' a bus at 1km, but cannot read it's route number, neither can an eagle.
 

Offline Chemistry4me

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« Reply #56 on: 17/04/2009 10:04:42 »
I can 'see' a bus at 100m; I can read it's route number at 100m; so can an eagle (if it could read). I can 'see' a bus at 250m, but I cannot read it's route number at that distance, an eagle can. I can 'see' a bus at 1km, but cannot read it's route number, neither can an eagle.
Well, I'm nearly convinced!
 

lyner

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Would we be able to see further if we had bigger eye-balls?
« Reply #57 on: 17/04/2009 11:03:19 »
With sufficient SNR, in hand, the diffraction limit isn't necessarily a limit. The Rayleigh Criterion is only a rule of thumb for conventional viewing. The real limitation comes from Mr Shannon (+edit)and this governs the amount of valid 'computer enhancement' possible.
Can you explain better?

This a signal processing topic. Imagine you have badly focused photo. You won't be able to read the number on the bus. If you know the characteristic of the optics, in detail, you can computer enhance the picture and get a better version of the number. This might, in a simple case, just involve the 'sharpen' control on your photo editor, which increases the contrast on edges. If you get it right, then you may see the number or you may see a wrong (look alike) number. Now imagine doing the same with a low light picture, in which the image has become speckled and 'noisy'. Even with the correct image enhancement, you can get the wrong bus number because of unfortunately placed speckles. Now imagine taking a series of low light photos, each with a different pattern of speckles, and averaging them to produce a new image with a lower level of speckledness. You then have a chance of getting the correct bus number - as with the original daylight picture.

Using a series of low light pictures (effectively using a longer exposure time), you have managed to increase the signal to noise ratio. The fundamental amount of information you can actually drag out of a picture actually depends upon the amount of speckle (or noise) on the picture - knowing details of the defects of your optics is, of course, essential.
 

Offline lightarrow

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« Reply #58 on: 17/04/2009 22:06:41 »
Precisely the point I have been making! Greater resolving power requires an improved retina
or a greater lens, up to the diffraction limit. Arrived at that limit, an improved retina is meaningless.

Quote
, which does not necessarily require a bigger eyeball, as the eagle's eye demonstrates.

When I suggested that 386,242.5 megapixels would be required to see your two 1mm spots on the moon, this really was 'tongue in cheek'. There really is no way any eye or camera could pick out such fine detail over such a great distance and for a retina to have this number of megapixels (cones) our eyeball would probably need to be the size of our head.
Here I don't understand because it seems to me a ripetition of your previous mistake: even if a normal eye, or a device of that dimensions, had 1,000,000,000,000,000,000,000 Megapixels, you won't be able to discriminate those two points in the Moon.

Quote
I can 'see' a bus at 100m; I can read it's route number at 100m
Because the bus is bigger than its route number...
 

Offline lightarrow

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Would we be able to see further if we had bigger eye-balls?
« Reply #59 on: 17/04/2009 22:11:32 »
This a signal processing topic. Imagine you have badly focused photo. You won't be able to read the number on the bus. If you know the characteristic of the optics, in detail, you can computer enhance the picture and get a better version of the number. This might, in a simple case, just involve the 'sharpen' control on your photo editor, which increases the contrast on edges. If you get it right, then you may see the number or you may see a wrong (look alike) number. Now imagine doing the same with a low light picture, in which the image has become speckled and 'noisy'. Even with the correct image enhancement, you can get the wrong bus number because of unfortunately placed speckles. Now imagine taking a series of low light photos, each with a different pattern of speckles, and averaging them to produce a new image with a lower level of speckledness. You then have a chance of getting the correct bus number - as with the original daylight picture.

Using a series of low light pictures (effectively using a longer exposure time), you have managed to increase the signal to noise ratio. The fundamental amount of information you can actually drag out of a picture actually depends upon the amount of speckle (or noise) on the picture - knowing details of the defects of your optics is, of course, essential.

You mean that, given enough time and computational power, you could get a detailed picture of an alien's garden in a planet 10 billions of light years from here, with a conventional telescope?
 

lyner

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Would we be able to see further if we had bigger eye-balls?
« Reply #60 on: 17/04/2009 22:32:26 »
That's effectively, what Shannon says, yes.
But, of course, the numbers count! It would take a huge amount of time because the SNR could only  be high enough with a very very small bandwidth (i.e. long observation time).
Already, they use 'good' images of (angularly) nearby stars to characterise the instantaneous aberrations due to atmosphere etc. and cancel them out to produce much better images of faint objects.
 

Offline LeeE

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Would we be able to see further if we had bigger eye-balls?
« Reply #61 on: 17/04/2009 23:17:40 »
This a signal processing topic. Imagine you have badly focused photo. You won't be able to read the number on the bus. If you know the characteristic of the optics, in detail, you can computer enhance the picture and get a better version of the number. This might, in a simple case, just involve the 'sharpen' control on your photo editor, which increases the contrast on edges. If you get it right, then you may see the number or you may see a wrong (look alike) number. Now imagine doing the same with a low light picture, in which the image has become speckled and 'noisy'. Even with the correct image enhancement, you can get the wrong bus number because of unfortunately placed speckles. Now imagine taking a series of low light photos, each with a different pattern of speckles, and averaging them to produce a new image with a lower level of speckledness. You then have a chance of getting the correct bus number - as with the original daylight picture.

Using a series of low light pictures (effectively using a longer exposure time), you have managed to increase the signal to noise ratio. The fundamental amount of information you can actually drag out of a picture actually depends upon the amount of speckle (or noise) on the picture - knowing details of the defects of your optics is, of course, essential.


There's a bit of a difference between enhancing an out-of-focus image and a low-light image.  As you say, if the characteristics of the optics are known it's relatively simple (although time consuming in practice) to model the lens and arrive at a limited set of sources that could have produced the blurred image.  With a low-light level image though, you've lost dynamic range and this can't be derived from the lens optics.

With the blurred image then, the data isn't lost but misplaced, but with a low-light level image the data is lost.
 

lyner

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Would we be able to see further if we had bigger eye-balls?
« Reply #62 on: 17/04/2009 23:38:32 »
There are two factors - the signal energy and the noise energy. If the signal energy is big enough wrt the noise energy, you can reconstruct the signal. The dimmer the picture is, the longer you need to look, to get enough signal. The higher the noise level is, the narrower bandwidth you need. Given long enough, the snr can be made arbitrarily high.
The "out of focus image" was only an example. The diffraction due to limited aperture is the bottom line with astronomy.
Read the basics of Shannon's theory; it's heavy going but it's the basis of all information transfer situations.
« Last Edit: 17/04/2009 23:42:14 by sophiecentaur »
 

Offline Chemistry4me

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Would we be able to see further if we had bigger eye-balls?
« Reply #63 on: 18/04/2009 02:07:19 »
the signal energy and the noise energy. If the signal energy is big enough wrt the noise energy, you can reconstruct the signal....the narrower bandwidth you need. ...the snr
...The diffraction due to limited aperture is the bottom line with astronomy...Shannon's theory.

Okay, so how does all this relate to eye-balls and seeing further? Does this answer the question?
 

Offline Don_1

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Would we be able to see further if we had bigger eye-balls?
« Reply #64 on: 18/04/2009 13:20:25 »
Precisely the point I have been making! Greater resolving power requires an improved retina
or a greater lens, up to the diffraction limit. Arrived at that limit, an improved retina is meaningless.

So you say an eagle, with a similar lens but a superior retina to ours, can see no better than a human?

Yes, a telescopic lens would be better for seeing over long distances, but such a lens requires more than one element. Our lens & that of an eagle (and cornea) is not a 'lens' in the sense of an optical camera or tele/microscope lens. These contain a number of fixed and moveable elements, our 'lens' is a single element which would be better described as a wide angle windscreen.


, which does not necessarily require a bigger eyeball, as the eagle's eye demonstrates.

When I suggested that 386,242.5 megapixels would be required to see your two 1mm spots on the moon, this really was 'tongue in cheek'. There really is no way any eye or camera could pick out such fine detail over such a great distance and for a retina to have this number of megapixels (cones) our eyeball would probably need to be the size of our head.
Here I don't understand because it seems to me a ripetition of your previous mistake: even if a normal eye, or a device of that dimensions, had 1,000,000,000,000,000,000,000 Megapixels, you won't be able to discriminate those two points in the Moon.

Isn't that what I said?


I can 'see' a bus at 100m; I can read it's route number at 100m
Because the bus is bigger than its route number...


I presume you intended this quote to be:
Quote
I can 'see' a bus at 250m, but I cannot read it's route number at that distance

To which you argue
Quote
Because the bus is bigger than its route number...

Yes, I can see the bus, but cannot discern the detail which my eye is incapable splitting into a fine enough image, but the eagle can do this, because it's retina has more cones and can, therefore, break down the image into smaller 'pixels' allowing the processor (the brain) to interpret the image in finer detail.
« Last Edit: 20/04/2009 08:04:23 by Don_1 »
 

Offline lightarrow

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Would we be able to see further if we had bigger eye-balls?
« Reply #65 on: 18/04/2009 15:29:45 »
So you say an eagle, with a similar lens but a superior retina to ours, can see no better than a human?
You wrote:
Quote
Greater resolving power requires an improved retina
and in my reply I wanted to point out that this answer is correct only *if you haven't already reached the diffraction limit*. I hope we can agree on it.

Quote
Yes, a telescopic lens would be better for seeing over long distances, but such a lens requires more than one element. Our lens & that of an eagle (the cornea) is not a 'lens' in the sense of an optical camera or tele/microscope lens. These contain a number of fixed and moveable elements, our 'lens' is a single element which would be better described as a wide angle windscreen.
But even if we had in our eyes moving parts as in a telescope, you could never be able to see those two points on the Moon.

Quote
Yes, I can see the bus, but cannot discern the detail which my eye is incapable splitting into a fine enough image, but the eagle can do this, because it's retina has more cones and can, therefore, break down the image into smaller 'pixels' allowing the processor (the brain) to interpret the image in finer detail.
Probably it's true (even if I sincerely don't know what and how eagles actually see) and you are right; what I intended is that, even with infinite pixels, you will reach a limit where you can still see the bus, but not the number, because of diffraction.
 

lyner

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Would we be able to see further if we had bigger eye-balls?
« Reply #66 on: 18/04/2009 22:52:20 »
The way the brain deals with images is quite complex. There is some spatial filtering (interconnections between adjacent sensors), apparently, which deals with some aberrations. Optically, the eye lens is not good but the overall performance is helped a lot by the filtering in the retina.

With an 'ideal' circular aperture, the  (spatial) impulse response (diffraction) is sinx/x and with appropriate inverse filtering, you can improve significantly on the half-power dip between two point sources (stars, for instance). But this inverse characteristic has the effect of magnifying the effect of noise so, to improve on the rayleigh criterion, you need progressively longer and longer exposure times. Worth it if you really need to resolve two objects but academic if you are just looking down your telescope!

It is really unfair to try to discuss performance of biological systems in terms of 'simple' Engineering / Physics. Evolution finds a compromise between cost and benefit. No animal will have 'better' eyesight than it needs. The Eagle is such a specialised feeder that it is susceptible to all sorts of environmental pressures which a Human can deal  with in ways other than by having 'better' eyesight. With Nature, it's a matter of compromise, always; with Technology, you just chuck more money at it.
 

Offline LeeE

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« Reply #67 on: 18/04/2009 23:19:22 »
There are two factors - the signal energy and the noise energy. If the signal energy is big enough wrt the noise energy, you can reconstruct the signal. The dimmer the picture is, the longer you need to look, to get enough signal. The higher the noise level is, the narrower bandwidth you need. Given long enough, the snr can be made arbitrarily high.
The "out of focus image" was only an example. The diffraction due to limited aperture is the bottom line with astronomy.
Read the basics of Shannon's theory; it's heavy going but it's the basis of all information transfer situations.

I read up on Modulation Transfer Function a long time ago, when I was still doing a lot of photography, but hadn't heard of Shannon's theory.  One day, when I'm in the mood I'll have a read of it.
 

lyner

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Would we be able to see further if we had bigger eye-balls?
« Reply #68 on: 19/04/2009 21:22:15 »
He IS the Daddy!
 

lyner

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Would we be able to see further if we had bigger eye-balls?
« Reply #69 on: 19/04/2009 23:25:06 »
MTF is the equivalent of frequency response for HiFi. It isn't the whole story but is a good start.
 

Offline Chemistry4me

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« Reply #70 on: 20/04/2009 01:11:11 »
Seeing as we've all come to some sort of an agreement, any last words to wrap up this thread?
 

Offline Don_1

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Would we be able to see further if we had bigger eye-balls?
« Reply #71 on: 20/04/2009 08:34:37 »
So you say an eagle, with a similar lens but a superior retina to ours, can see no better than a human?
You wrote:
Quote
Greater resolving power requires an improved retina
and in my reply I wanted to point out that this answer is correct only *if you haven't already reached the diffraction limit*. I hope we can agree on it.

Quote
Yes, a telescopic lens would be better for seeing over long distances, but such a lens requires more than one element. Our lens & that of an eagle (the cornea) is not a 'lens' in the sense of an optical camera or tele/microscope lens. These contain a number of fixed and moveable elements, our 'lens' is a single element which would be better described as a wide angle windscreen.
But even if we had in our eyes moving parts as in a telescope, you could never be able to see those two points on the Moon.


Yes & yes.

It is suggested (based on observation) that eagles can define objects at a distance of 2.24 times greater than that of a human.

A larger eyeball would not necessarily increase the distance at which an object can be observed. A wider pupil would allow more light into the eye, giving improved vision in low level light, as is the case for nocturnal animals such as owls and cats. An increased number of cones on the retina would give improved definition by breaking down the image into more precise information, allowing the brain to create an image of a higher clarity, thus making parts of that image, which are indefinable with the number of cones our retina currently has, definable. But ultimately, the distance at which an object can be defined is not dependant solely on the size and/or quality of the eye. Since the eye is a receiver, it can only translate the light it receives into a signal which the brain converts to an image. The distances at which we can define objects are equally governed by the constraints of the physical properties of light as it travels through space and/or our atmosphere and its passage through our cornea and the saline wash keeping it clean. During its passage from object to eye, dust, water vapour, strong gravitational fields, our cornea and its ‘screen wash’ can distort and diffract the light. An improved eye would simply produce a clearer image of that distorted and diffracted light; it would not be able to reconstitute the light into its original undistorted and un-diffracted pattern.

How's that?
 

lyner

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Would we be able to see further if we had bigger eye-balls?
« Reply #72 on: 20/04/2009 08:58:33 »
Doesn't the digital camera situation say it all?

The best compact cameras with small sensor areas and small lenses are never as good as the best SLRs with larger sensors and larger lenses. `the resolution is better because there is more room for sensors and the noise performance is better because the sensors area is greater.

Why do you think all the 'best' quality photos are taken on large format film cameras?
 

Offline Chemistry4me

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Would we be able to see further if we had bigger eye-balls?
« Reply #73 on: 20/04/2009 09:00:28 »
Come on Doris, stop talking in riddles! :)
 

Offline Chemistry4me

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« Reply #74 on: 20/04/2009 09:11:05 »
A larger eyeball would not necessarily increase the distance at which an object can be observed. A wider pupil would allow more light into the eye, giving improved vision in low level light, as is the case for nocturnal animals such as owls and cats. An increased number of cones on the retina would give improved definition by breaking down the image into more precise information, allowing the brain to create an image of a higher clarity, thus making parts of that image, which are indefinable with the number of cones our retina currently has, definable. But ultimately, the distance at which an object can be defined is not dependant solely on the size and/or quality of the eye. Since the eye is a receiver, it can only translate the light it receives into a signal which the brain converts to an image. The distances at which we can define objects are equally governed by the constraints of the physical properties of light as it travels through space and/or our atmosphere and its passage through our cornea and the saline wash keeping it clean. During its passage from object to eye, dust, water vapour, strong gravitational fields, our cornea and its ‘screen wash’ can distort and diffract the light. An improved eye would simply produce a clearer image of that distorted and diffracted light; it would not be able to reconstitute the light into its original undistorted and un-diffracted pattern.

How's that?

Hmmm...not bad, not bad at all.
But really! Strong gravitational fields! Is that necessary? :D
 

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