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Would we be able to see further if we had bigger eye-balls? 
Perhaps I have not explained myself properly? I was thinking if we had a bigger lens would we be able to see further (i.e, have higher visual acuity)?
We can say that size doesent really matter in sense organs I think Hawk or an Eagle can point out their prey from high distance wven the diametre of eyeballs is just about 1-2 cms!!!!! Quiet amazing creatures.......     
Okay, forgetting about the cones for a second. If we had eyes the size of oranges our vision would be improved right? 
In astronomy it is important to have a very large aperture because the light levels are extremely low. You can also avoid aberrations by using a parabolic reflector. This concept has never evolved naturally - I blame biologists :-)
I guess we have evolved eyes that are adequate for our use.
As to this thread's question, I should think a larger eye would not be necessary for improved long distance vision.
That's fascinating stuff. You want me to change the title of the thread LeeE (even though I know you have a thing against it)?
Quote from: Don_1 on 13/04/2009 14:04:06As to this thread's question, I should think a larger eye would not be necessary for improved long distance vision.Certainly, I agree with it. But it depends on how much "long distance". If you want to increase that distance a lot, before or less you'll have to increas the eye's dimensions.
There are two factors (at least in the main, for this discussion) - resolution and sensitivity. To get more resolution you need more sensors looking at a particular field of view. There is a limit to how sensitive a receptor or photosensor can get. To get more sensitivity you need to increase the total light gathered by having as wide an aperture as possible. Astronomical telescope design has always been about trying to achieve this whilst keeping aberrations to a minimum because the amount of light arriving from distant stars is very, very small indeed. The other way to improve the light gathered is to stay "on-target" for a long time to integrate the total light gathered - a long exposure. Hubble does both of these things by having a large parabolic (at least it was supposed to be) reflector and very steady positioning with no nasty effects from the light passing through the atmosphere. In fact I just looked up Hubble and its CCD array (image sensor) is actually only 2.5 Mpixel, which is very poor by today's standards.
Quote from: lightarrow on 13/04/2009 14:59:35Quote from: Don_1 on 13/04/2009 14:04:06As to this thread's question, I should think a larger eye would not be necessary for improved long distance vision.Certainly, I agree with it. But it depends on how much "long distance". If you want to increase that distance a lot, before or less you'll have to increas the eye's dimensions.I'm not so sure that this would be the case. I can look at the Moon, without the need for a telescope, and quite clearly make out the surface detail (to an extent). I think if I wanted to be able to make out more detail of a far distant object, it is more the sensor (retina) which requires extra capability than the receiver.Let me explain my reasoning here.Take a Nikon D40 - 6 megapixel DSLR body and fit a Nikon 85mm f2.8 lens. With the lens set to infinity, take a shot of an object on the horizon. Now, using your computer as the processor, enlarge that object to the maximum at which it remains discernable. Now compare that with the identical shot, taken under identical conditions with the same Nikon 85 mm f2.8 lens, but using a Nikon D3x 24.5 megapixel DSLR body.The extent to which this shot can be enlarged with the object remaining discernable will be much greater (approx. 4 X greater), yet it is the result from the very same lens and the same processor, only the sensor has been improved.Our eye works in much the same way as this camera with a fixed focal length lens. We make sense of a particular object within our field of vision by focusing the lens on that object and then getting the brain to concentrate on it. With an improved sensor, we would be able to distinguish more detail of that object.The eagle has an eyeball roughly the same size as a human, yet it can see far better than a human. The reason for this is that the human retina has 6.4m cones, 200k of which are in the fovea, the eagle has approximately 32m cones, 5 times that of a human. The back of the eagle’s eyeball is flatter and the retina bigger, but the lens is not much different. The brain works in a similar way to a digital zoom on a camera. It concentrates on one area of the whole picture. If that picture has a higher resolution, it can make more sense of the detail. In effect, we ‘digitally’ zoom in on an object.If we (and eagles) were to be able to zoom in on an object optically, in the same way as a camera zoom lens, our eye would need to be restructured since eyes have a single element lens. To enable optical zooming, like a camera lens, eyes would need a multiple moving element lenses. This would create a problem, however, in that there would be a considerable loss of field of vision.In conclusion, our eyeball does not need to be bigger in order to see further. We can see just as far as an eagle. What it needs is an improved retina in order to be able to discern more from a small area of that sensor.
lightarrow To discern 2 x 1mm points 1mm apart on the Moon's surface is rather going to the extreme. The sensor required for this, I think, would need 386,242.5 megapixels. This would mean fitting more than 10k times more cones on an eagle's retina, or 50k more times for a human. This would hardly be termed as 'being able to see a long way', this is rather into the realms of Superman!
In answer to Lightarrow's question, wouldn't it be possible to discern these two 1mm spots with a camera if you could get enough magnification, if you could keep the camera and lenses still enough, and if you could have an appropriate exposure time?
You had me worried there sophiecentaur.Look at this pictureThis was taken on my Nikon D300 12.3 mp and printed (slightly cropped)to 36" x 22"If this had been taken on a 6mp camera, it would not be possible to print to this size without the diagonal lines being out of kilter. To get a print any bigger than this, I would need a camera with more pixels to its sensor.
Does anyone know what the typical angular resolution of the eye is and how it compares to the diffraction limit?
PS Have you got some dirt on your sensor? (Top left)
Not even Superman could do it,
The point I am making is that we do not need a bigger eyeball to see further....
Quote from: Don_1 on 16/04/2009 09:06:22The point I am making is that we do not need a bigger eyeball to see further....Is that your final answer? 
Quote from: sophiecentaur on 15/04/2009 22:51:16PS Have you got some dirt on your sensor? (Top left)Yes, there was a speck of dust which I hadn't noticed until the print was done! Details of shot:Lens focal length 80mm ; f18 @ 1/1250sec ; ISO 200 ; re-colouring with Nikon Capture NX.
Quote from: lightarrow on 15/04/2009 18:38:19Not even Superman could do it, I think you will find all of that a mere trifle to Superman; he can do anything!As BC has cottoned on, I am really being hypothetical and not taking distortion into account. In practice, even over a relatively short distance atmospheric distortion would render ultra long vision pretty worthless. But, by the same token, our brain does account for and correct distortion caused by our fixed focus lens. For starters, the image projected onto the retina is upside down. Looking at an object a few cms away causes this effect:But our brain compensates for this and we see the object in a more natural way. Our brain also merges two different views to give us 3d vision.The point I am making is that we do not need a bigger eyeball to see further. Again as BC pointed out, and as I said in a previous post, our eye can already see far distant objects. I cannot be sure of this, but I think V762 Cas (in Cassiopeia) is the furthest star from Earth visible to the naked eye. 15000 light years, I think is plenty far enough. Our eye's resolution, however, could be much improved with a sensor (retina) matching the quality of that of an eagle. Since the eagle's eyeball is the same size as a human eyeball, I see no need for a larger eyeball to improve our resolution.
So altogether, what do we need to take into consideration here?