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If lenses cause chromatic aberration, how come we don't see it with our own eyes?

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#1 starcruiser

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Posted 26 June 2019 - 10:17 PM

I mean the human eye is only a single lens system, how is it that we don't see any color fringing at all in our vision but we see it easily with an artificial lens?


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#2 jaraxx

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Posted 26 June 2019 - 10:37 PM

Because our eyes aren't made of glass?

 

Also, there are times that I see "fringing" when I look at bright objects, especially high contrast against the dark. Not sure it's color fringing, exactly...



#3 jerahian

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Posted 26 June 2019 - 10:38 PM

We do experience chromatic aberration, however our brain corrects for it.  Think of it as highly evolved post-processing.  We are most sensitive to green, and our brain adjust for the higher and lower wavelengths being slightly out-of-focus.


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#4 Michael Covington

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Posted 26 June 2019 - 10:40 PM

Also, we only have sharp vision in the very center of the field, where chromatic aberration is less than elsewhere.


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#5 JimFR

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Posted 26 June 2019 - 10:56 PM

Our eyes are very wide angle, too wide to detect the CA.  We notice it in lenses due to magnification, which magnifies the effect of CA.



#6 lylver

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Posted 27 June 2019 - 01:33 AM

In center of eye, retina structure is very specialized and we are protected by a yellow filter (a natural pigment) that limit the blue chromatic aberration.

there is quite no sensitivity to blue (S type cone, rods) in the center of the retina.

Source : Handbook of Optical System (H.Gross)

retina-structure.JPG

 

 

From Evans (1974) : spectral discrimination is found special in low illumination : at mesopic limit

 

A very few change in luminance around 492nm (F ray and O III ray), and D ray 589 and further ... ~600 is better perceived.

 

It is as important as the optimal contrast range and can be contradictive with the optimal spherical aberration tuning at 555nm for the today apo that is a generic indication. There is some big miss for some apo that are not good enough at 590-610nm color range for planetary observing.

 

Old achromat were visual tuned around 555nm for minimal star spot/max brightness, 573-575nm for visual color balance, 580nm for specialized planetary.

All had spherical highly corrected globaly and centered at D ray. (source : Danjon & Couder)

 

Modern achromat, with lower f/D around 10 ou less, are often tuned in green for brightness and small spot size in deep sky. Some are heavily balanced toward blue/green to limit purple halo, so don't use them in terrestrial/planetary observation, filter them on Moon.

 

luminosite-discrimination-couleur.JPG


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#7 TOMDEY

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Posted 27 June 2019 - 01:50 AM

I mean the human eye is only a single lens system, how is it that we don't see any color fringing at all in our vision but we see it easily with an artificial lens?

 

Hi, starcruiser; Great question and ostensible concern!

 

We DO have significant, traditional Longitudinal Chromatic Aberration. My recollection is that it's about 1/6 Diopter, "undercorrected".

 

OK... OK... I just computed it from 1st principles, assuming that the human eye has a 1-inch focal length and is made of water and I get 0.29 Diopter (@450-650nm)... reasonably in the ballpark of my recollection... especially considering that there is more stuff in there and different dimensions. Optometrists generally refract eyes to about a quarter of a diopter accuracy... but a really scrupulous patient (like me) can discriminate differences of about a tenth of a diopter. So, the chromatic of our eye is just enough to be pretty annoying... depending on how picky you are.

 

Our eyes also have traditional (Seidel lateral cubic) Spherical Aberration. And that is quite substantial for dilated pupil. Lens Implants and/or Lasik/PRK actually correct the ~natural~ spherical aberration of the human eye! I had those surgeries done and actually do enjoy the hyper-acuity consequent of those improvements. 20/12.5 each and both eyes... even with dilated pupils. And that makes it really nice for enjoying things like star clusters. I just don't need as much magnification as my companions, to see all the detail. Worth considering, as an additional motivation to get one's eyes done. I've commented before that when I look out at the yard (post improvements)... that every blade of grass, tree twig, etc. looks razor sharp. I'm not kidding --- the improvement is that dramatic!    Tom

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#8 Harold88

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Posted 27 June 2019 - 02:01 AM

I will give you an example. 

 

Did you ever heard someone after watching a DLP projector saying that he could see rainbows on the screen?



#9 ngc7319_20

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Posted 27 June 2019 - 02:27 AM

I mean the human eye is only a single lens system, how is it that we don't see any color fringing at all in our vision but we see it easily with an artificial lens?

One way to see the chromatic aberration is a follows: look at Jupiter at moderate high magnification -- like 25 to 50 power per inch of aperture.  View and focus as normal.  But then move your head a few mm to the left or right, so that you are no longer viewing through the center of the eye pupil, but instead are viewing off center and towards the edge of the pupil.  You will see color fringing on the planet image -- one side of the image will be blue and the other will be red.

 

Another way to see it, is looking at tiny LED Christmas lights of different colors.  You will see that the red ones and blue ones do not focus at the same time.


Edited by ngc7319_20, 27 June 2019 - 06:40 AM.

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#10 HydrogenAlpha

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Posted 27 June 2019 - 05:32 AM

I can see it actually. On a bright day, look at a dark rectangular object against the sky. You might be able to see blue fringing on one side, and reddish fringing on the other. 


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#11 Astrojensen

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Posted 27 June 2019 - 11:49 AM

I can see it quite well, too, with the naked eye, when looking at the Moon at night. 

 

 

Clear skies!
Thomas, Denmark


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#12 jay.i

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Posted 27 June 2019 - 11:56 AM

Sadly, I have also "trained" myself to see it. It usually happens on high contrast objects, like shiny metal thresholds between rooms (separating carpet/tile/wood), shiny elevator doors, shiny balcony railings, metal pipes, all sorts of very bright, very high contrast objects. It's never when the object is in the center of my vision with my focus on it; it's always when the object is at the edges of my vision, and I can sort of "pay attention" to the object without actually moving my eyes to look directly at it.

 

Trust me, in no way do I consider this a skill. :'(


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#13 Jon Isaacs

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Posted 27 June 2019 - 12:05 PM

Something to consider:

 

At a 2 mm entrance pupil with the bright image,  eye is operating at near full resolution and cones are operating.

 

The eye has a focal length of about 17 mm, that's F/8.5.

 

A 2 mm F/8.5 lens has a chromatic ratio of about 100. Were it glass, the chromatic aberration would be within reason..

 

Jon


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#14 HydrogenAlpha

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Posted 27 June 2019 - 01:20 PM

Sadly, I have also "trained" myself to see it. It usually happens on high contrast objects, like shiny metal thresholds between rooms (separating carpet/tile/wood), shiny elevator doors, shiny balcony railings, metal pipes, all sorts of very bright, very high contrast objects. It's never when the object is in the center of my vision with my focus on it; it's always when the object is at the edges of my vision, and I can sort of "pay attention" to the object without actually moving my eyes to look directly at it.

 

Trust me, in no way do I consider this a skill. :'(

I don't think I trained myself to see it. It's just something I noticed since I was young, and only figured out it was due to CA sometime later. 


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#15 jay.i

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Posted 27 June 2019 - 01:26 PM

I don't think I trained myself to see it. It's just something I noticed since I was young, and only figured out it was due to CA sometime later. 

I never noticed until I became a refractor snob and start looking for optical aberrations in everything. "If I could turn back time...." wron.gif


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#16 lylver

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Posted 27 June 2019 - 01:28 PM

to go further with Jon explaination

What are normal capability of the eye ? I show common medical consideration that may have evolved.

Less correction is needed for blue, S cones are fewer than M and L cones (1S for 5M and 10L). Aberration is more easier corrected going to red.

Human-Eye-precision.JPG

Image-quality.JPG

defocusing-internal.JPG

--------------------------------

According to Danjon & Couder, standard 1935 refractor tuning for deep sky

Spot size for luminosity/brightness/smaller spot size (first), visual color prefered balance (second)

D&C-luminosity.jpg D&C-color-balanced.jpg

For standard yellow focusing @573/575nm (~terrestrial)

D&C-luminosity-std-yellow.jpg D&C-visual-std-yellow.jpg

a bit surprising for the last spot structure.

Note : deep blue is 486nm, cyan is 507nm.

---------------------------------------------------------------

There is a recent study that try to explain chromaticity.

https://www.handprin...or1.html#newpsf

 

A final observation is that the white point is not located on the luminosity function. This simply demonstrates that white is not the same as bright.

If we turn this diagram to look at it sideways, we see that the boundary of color space is geometrically irregular. No simple geometrical shape can describe the spectrum locus.

Luminosity is the V line and changes when S cone activates... around the 525nm limit.

The white point position is ... odd. Surprisingly, analysing old achromat color balance using spot size, green 525nm is equal size as deep red°.

white-point.JPG D&C-visual-green525.jpg

 

So about chromatism feeling, it is complex to say if you see chromatical aberration or no. There are variations between people, intensity of light and global image color composition, how the instrument behave...

Achromatism definition should cover a great number percentage of the population.

 

° : in fact as contrast is mainly depending on L and M cone sensitivity, there is a significant decrease if wavelength is higher than 525nm.


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#17 starman876

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Posted 27 June 2019 - 08:48 PM

I want a brain focusing system for my telescope.



#18 Michael Covington

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Posted 27 June 2019 - 09:34 PM

I want a brain focusing system for my telescope.

It's possible to autofocus on the retina.  It involves a beamsplitter so that the instrument can look into your eye (through the lens) while the eye is looking at an image.  You may have experienced one of these at the eye doctor -- it's a quick automated way to measure your eyeglass prescription, but it's not as accurate as a full examination, so it's used only as a quick sanity check to confirm other measurements.  It would be possible to focus a telescope the same way, at least if there are reasonably bright objects in the field.


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#19 KerryR

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Posted 28 June 2019 - 09:44 AM

Hi, starcruiser; Great question and ostensible concern!

 

We DO have significant, traditional Longitudinal Chromatic Aberration. My recollection is that it's about 1/6 Diopter, "undercorrected".

 

OK... OK... I just computed it from 1st principles, assuming that the human eye has a 1-inch focal length and is made of water and I get 0.29 Diopter (@450-650nm)... reasonably in the ballpark of my recollection... especially considering that there is more stuff in there and different dimensions. Optometrists generally refract eyes to about a quarter of a diopter accuracy... but a really scrupulous patient (like me) can discriminate differences of about a tenth of a diopter. So, the chromatic of our eye is just enough to be pretty annoying... depending on how picky you are.

 

Our eyes also have traditional (Seidel lateral cubic) Spherical Aberration. And that is quite substantial for dilated pupil. Lens Implants and/or Lasik/PRK actually correct the ~natural~ spherical aberration of the human eye! I had those surgeries done and actually do enjoy the hyper-acuity consequent of those improvements. 20/12.5 each and both eyes... even with dilated pupils. And that makes it really nice for enjoying things like star clusters. I just don't need as much magnification as my companions, to see all the detail. Worth considering, as an additional motivation to get one's eyes done. I've commented before that when I look out at the yard (post improvements)... that every blade of grass, tree twig, etc. looks razor sharp. I'm not kidding --- the improvement is that dramatic!    Tom

Tom,

Not to hijack the thread, I know this is off-topic, but:

Did you get the same "distance focusing" lens in both eyes? Are you 'forced' to use readers for close-up? I'm assuming you had lens replacement for cataracts. I know surgeons seem to prefer other solutions, such as one eye close-focus, the other distance-focus. I've heard they're hesitant to make both eyes distance-specific.

I'm certain cataract surgery is in my future, based on my increasingly reduced violet sensitivity with my achromats! (And I have cataracts, but it's not currently known if they're congenital or progressive.)



#20 TOMDEY

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Posted 28 June 2019 - 11:11 AM

Tom,
Not to hijack the thread, I know this is off-topic, but:
Did you get the same "distance focusing" lens in both eyes? Are you 'forced' to use readers for close-up? I'm assuming you had lens replacement for cataracts. I know surgeons seem to prefer other solutions, such as one eye close-focus, the other distance-focus. I've heard they're hesitant to make both eyes distance-specific.
I'm certain cataract surgery is in my future, based on my increasingly reduced violet sensitivity with my achromats! (And I have cataracts, but it's not currently known if they're congenital or progressive.)

Hi, Kerry! Ophthalmologist Surgeons now offer ~True Astronomical Infinity~ correction, both eyes, dark-adapted open pupils, rather than the usual default of closer in, constricted pupils, not quite able to focus out to the stars. Our local guy here, at the teaching hospital, includes that option right in his marketing literature! Keep in mind that you entirely lose focus accommodation when your old cloudy yellow bio-lenses are replaced with pristine clear prosthetics. The implants also correct your astigmatism and even the ~natural~ spherical aberration of the human eye! Your vision will become laser sharp day and night true infinity. If there is any small (typically tiny) residual focus and/or astig remaining... PRK and/or very mild "no line" glasses will take care of that. My final correction, after the surgeries and settling-in time... came out perfect 20/12.5 Dark Adapted in one eye and the other also measures 20/12.5, but has tiny remaining astigmatism... tiny. So the stars look like miniscule bright dots.

 

I have progressive eyeglass lenses so I can read thru the bottoms and see infinity through the tops... plus that little astig correction on one side. With the glasses off, I can't read! Getting one eye far and one close is a pretty debilitating compromise. Even worse are surgeries that focus near with one zone of the lens and far with the other --- so you can resolve both but never again see anything very well focused! My surgeon strongly suggests against those... will only do that if the patient demands them and signs off on vision quality.

 

Regarding congenital/progressive nature of eye lens degradation. We all have a combination. The congenital component, you can be lucky or unfortunate, but never immune... we all have human genes; progressive, we all suffer that too. A lot of sun can accelerate the degradation, but it's as inexorable as wrinkly skin. And... just like wrinkly skin... gets quite noticeable around age thirty-five. That from my optometrist... he said he looks in there and can tell a person's age quite accurately... the eyes' interior don't lie! He then commented that people would opt for the surgeries at 35, if cost were no object; I got mine done at 65 and WOW! But, optometrists are not going to tell you that unless you press the issue. Just like your Primary Care doctor won't tell you that your skin is getting wrinkly. And friends won't tell a 35-year-old that she looks 35... they'll politely "guess" twenty.

 

Most of us (even astronomers) are very tomophobic... throwback to mom cautioning, "Don't poke your eye out!" That puts us in a state of denial, "Oh, my eyes are still perfect... Ehhh... perfect!" Yeah... and I'm 35, going on 72!

 

Results may vary.

 

[Here, Tom heads off to a different surgeon, for a facelift, tummy tuck consultation... followed by tattoos and piercings.]    Tom

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#21 KerryR

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Posted 28 June 2019 - 11:38 AM

Thanks, Tom, for that detailed post! I'm pleased to hear that there is an awareness in the market for astronomical requirements. Of course, I'm not yet aware of what options surgeons in my area offer, but I suppose they could order any lens I requested.



#22 TOMDEY

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Posted 28 June 2019 - 12:00 PM

Thanks, Tom, for that detailed post! I'm pleased to hear that there is an awareness in the market for astronomical requirements. Of course, I'm not yet aware of what options surgeons in my area offer, but I suppose they could order any lens I requested.

It will be if the surgeon is familiar and comfortable with that ~true infinity~ aspect. The (much more) common default is to correct for daytime and somewhat closer in than infinity... probably some play on the hyperfocal range or even closer. So that you can legally drive sans glasses but still see sort of near as well... neither ideally. The astronomy infinity correction targets best correction far away. I've also been through this discussion with optometrists ad nauseam and many/most insist that it doesn't make any difference --- those are the guys to avoid, because they won't deviate from their standard practice and the patient is just there to annoy them.

 

[Here Tom is revealing his conceit that most technologists are just crank-turners, and didn't really excel or care about understanding the underlying theory. MDs and PhDs are not immune. Most of them just turn the cranks, very fancy cranks!]    Tom 



#23 KerryR

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Posted 28 June 2019 - 12:08 PM

It will be if the surgeon is familiar and comfortable with that ~true infinity~ aspect. The (much more) common default is to correct for daytime and somewhat closer in than infinity... probably some play on the hyperfocal range or even closer. So that you can legally drive sans glasses but still see sort of near as well... neither ideally. The astronomy infinity correction targets best correction far away. I've also been through this discussion with optometrists ad nauseam and many/most insist that it doesn't make any difference --- those are the guys to avoid, because they won't deviate from their standard practice and the patient is just there to annoy them.

 

[Here Tom is revealing his conceit that most technologists are just crank-turners, and didn't really excel or care about understanding the underlying theory. MDs and PhDs are not immune. Most of them just turn the cranks, very fancy cranks!]    Tom 

This is very helpful information. Sounds like I'll have to spend considerable time and care choosing a provider, and not get suckered in to the standard comfy-for-the-surgeon solution... This won't be happening any time soon for me (I don't think) but I really appreciate first-hand astro-specific information, which I will most certainly be making use of in the not-too-distant future!


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#24 starman876

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Posted 28 June 2019 - 12:34 PM

It's possible to autofocus on the retina.  It involves a beamsplitter so that the instrument can look into your eye (through the lens) while the eye is looking at an image.  You may have experienced one of these at the eye doctor -- it's a quick automated way to measure your eyeglass prescription, but it's not as accurate as a full examination, so it's used only as a quick sanity check to confirm other measurements.  It would be possible to focus a telescope the same way, at least if there are reasonably bright objects in the field.

it will sure make focusing a snap and we will no longer hear complaints about my mount shakes too much. 



#25 macdonjh

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Posted 28 June 2019 - 12:43 PM

New topic about eye surgery here: 

https://www.cloudyni...ment-et-cetera/

 

I couldn't resist replying, but didn't want to continue to hijack this thread.  Thanks to lylver for all that science that is, unfortunately, way over my head.  I'll have to read it again.  And again.




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