Colour blindness (1 Viewer)

I wondered if the reason that some observers notice CA in binoculars more than others is partly due to colour blindness.

There are various types of colour blindness, and according to one article it affects 8% of men and 0.5% of women.

It lists the various types, and a nice statement says that people with colour blindness see the world as people with full colour vision see it at dusk or dawn.

I have not researched the subject but I see colours well despite colour blindness in the family.
My two eyes see colours slightly differently.

I don't think that I see far into the blue or red.
Some people see into UV and infra red.

With me I notice CA quite easily when testing optics but can ignore it while observing.

My most used telescope is a 5 inch f/5 Jaegers refractor, with a lot of CA.
It affects intensity estimates on Saturn and fine detail. The maximum useful power is 145x, whereas my longer focus 5 inch refractors are really excellent at 250x or more.

I wonder how birdwatchers with different types of colour blindness do with recognising bird species?
Perhaps it doesn't matter too much?

B.

Interesting! But I'm sorry for you if this could cause you problems. I do not know the specific subject and it has always intrigued me to know how they see colorblinds at any level, because it is still a scientific subject with objective values.

Most CA is often achromatic and involves purple and green. Or at least this is perceived in most cases of achromatic objectives. But in my opinion the experiences reported are often the result of a lack of knowledge in optical matters and also of incorrect adjustments of the binoculars. Which, although it is also suitable for children, a certain skill and experience is always required to use it to the fullest

Quite interesting B! Surprising that men are affected more so than woman. Will have to do some searching on this.

KC Foggin said:

Quite interesting B! Surprising that men are affected more so than woman. Will have to do some searching on this.

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How about some wild speculation?

When human-kind was evolving it is likely the females were the ones who looked after the babies. Probably they collected fruits and berries more than the men who were more likely to have been hunters than gatherers. Accurate colour may have benefitted the women so that they more reliably avoided poisonous fruits and berries when gathering food for babies. Accurate colour may not have been so important for the men.

Lee

That's the/a theory indeed.

Just depends on which chromosome the “defect” is, X. women have a “spare”so they are far less susceptible to it. Need to explain CA, then I can see if a deuteranope can see it worse.

Peter

To keep it simple, give or take a little, the focussing power of the lens of the eye and cornea combined is about 60 dioptres, with a focal length of about 22mm. The result will be substantial levels of CA at the retina. The brain learns to remap the aberrations through infancy to produce a crisp, aberration free mental image. It's firstly how much your brain has learned to adapt to variation in CA levels that is probably the first determinant on whether you see additional CA with binoculars ot not, but it also explains why some at least can conciously alter their apparent sensitivity.

The reason for the difference in occurrence of colour blindness between men and women is the genes for the M and L (green and red) receptor pigment is carried on the X-chromosome. Women have two X-chromosomes and men an X and a Y. Normally it would require both copies to be faulty for a woman to have the more common forms of colour blindness, a relatively rare occurance, but a man only the one.

There are much more common variants in the L-pigment in particular that cause a more subtle alteration in colour distinction and perception. About 50% of men will have a relatively slight red/green impairment, but again, a lower proportion of women. I've seen claims that this mutation also alters sensitivity in the violet and deeper red wavelengths, but I've not seen the data. In fact women may often have one normal and one abnormal copy on each chromosome. Though not so common there is a similar amino acid substitution on the M-opsin (green) pigment. There are reports that women who have both variants of the red and both of the green, and effectively have 5 colour receptors, do substantially better in colour discrimination tests than the other genetic groupings

I'm not aware that there has been any investigation into how genetics might affect CA perception, but I think it's reasonable to speculate that it might play a part.

David

Hi,

Binastro said:

I wonder how birdwatchers with different types of colour blindness do with recognising bird species?
Perhaps it doesn't matter too much?

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Well, the irony is that even if you're a human with no form of colour blindness, you're pretty much colour blind in comparison to the colour perception abilities of a bird.

Bird have receptors for four different and markedly distinct colours, and these receptors have sharply defined selectiveness.

Humans only perceive three different colours, their perceptors are not very selective, and two of these colours are fairly close to each other in the spectrum, so their value for visual information gathering is not terribly high.

However, being colour blind does have advantages too: In a military context, it was found that colour-blind soldiers did not fall as easily for some types of camouflage as their normal-sighted comrades, for example when the camouflage employed distractive splotches of colours to break up the shape of whatever it was meant to conceal.

I believe in one of his books, Richard Dawkins points out that there is a primate species which has a ratio of colour blindness among males of a stable 50% (or something), so it's clear that whatever the mechanism behind it, the colour-blind males have some advantage fully compensating the disadvantages of not being able to discern colours as well as the other half of the male population.

I would imagine that it's slightly harder to tell apart certain bird species if you're a colour-blind human, but as for many species, colour is not an essential field mark for identification, it might not be an actual issue for the practical bird watcher.

However, given the high ratio of colour blindness among human males, I think there's probably someone with the actual experience on the forum to give us a first-hand account

All I can say is that in my brief time serving as army medic, I ran hundreds of soldiers through the Ishihara test for colour blindness, and only a handful of them showed any signs of actual colour blindness. However, there might have been a certain bias in the set of test persons ... maybe if you were colour blind, you'd not normally be eligible for duty as army aviation ground crew.

What struck me that colour blindness apparently wasn't the same for everyone, as there were guys who could figure out the coloured numbers and shapes of the Ishihara test because they were still able to see faint traces of it, and others who declared they couldn't even see a trace of the colours.

https://en.wikipedia.org/wiki/Ishihara_test

Quite a fascinating topic, and I always wonder how birds with their superior colour perception see one another!

Regards,

Henning

You want the “put these coloured dots into order” test... then look at the resulting pattern, very interesting and more discriminating. Remember that many mammals are colour blind.

Peter

wllmspd said:

You want the “put these coloured dots into order” test... then look at the resulting pattern, very interesting and more discriminating. Remember that many mammals are colour blind.

Peter

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Many small, nocturnal mammals are red-blind.

typo said:

To keep it simple, give or take a little, the focussing power of the lens of the eye and cornea combined is about 60 dioptres, with a focal length of about 22mm.

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Hi David, if I may correct, 60 diopters is not the power of focus. 60 diopters is the dioptric power of the average normal human eye (without defects). The inverse value of the dioptric power (1/60) is the focal length in meters, of the same eye. In this case, approximately 16.5 mm (variable between 16 and 17 mm).
The number 22 says almost nothing, or approaches the average value of the diameter of the normal eyeball, which is 24 mm.

typo said:

The result will be substantial levels of CA at the retina.

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It is not clear to me what you mean. Forgive my direct and perhaps rhetorical language, but I have no intention of attacking or offending you or anyone else. Of course, the CA are the effect of a wrong focus of various colors. Our crystalline lens (eye lens) is aspherical and / or in any case of variable shape, our retina lies on a spherical plane. Why should the information you gave (which I have corrected) be the cause of the CA?

wllmspd said:

Just depends on which chromosome the “defect” is, X. women have a “spare”so they are far less susceptible to it. Need to explain CA, then I can see if a deuteranope can see it worse.

Peter

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Hi,

thanks for pointing that out - which is the reason for higher numbers of colorblindness in males.

Joachim, who can occasionally see CA but is rarely bothered by it - at least in binoculars

Rico70 said:

Hi David, se posso correggere, 60 diopters is not the power of focus. 60 diopters is the dioptric power of the average normal human eye (without defects). The inverse value of the dioptric power (1/60) is the focal length in meters, of the same eye. In this case, approximately 16.5 mm (variable between 16 and 17 mm).
The number 22 says almost nothing, or approaches the average value of the diameter of the normal eyeball, which is 24 mm.


It is not clear to me what you mean. Forgive my direct and perhaps rhetorical language, but I have no intention of attacking or offending you or anyone else. Of course, the CA are the effect of a wrong focus of various colors. Our crystalline lens (eye lens) is aspherical and / or in any case of variable shape, our retina lies on a spherical plane. Why should the information you gave (which I have corrected) be the cause of the CA?

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Rico,

I think I'm guilty of trying to oversimplify what I've learned from multiple sources, which do have quite a few inconsistancies. The 60 dioptre value is usually quoted as the total corrective power of the eye including focal accommodation, but of course, that will reduce with age. Various sources suggest the lens to retina distance may range from about 19mm to about 27mm and usually come up with between 22mm and 24mm as the modal value. I know some sources do suggest the focal distance is about 16.5mm, but that is in the object plane, not the image plane. I've read anatomical studies that suggest a mean of about 22mm as well. My wife's opthalmic surgeon told me that 22mm is more consistent with her own typical optical estimates, though acknowledged some historic texts suggested a higher value. She thought that the discrepancy could be explained by different instrumentation and sample groups. Our ophthalmologist was very impressed with her results.:t:

The simple lens system of the eye will produce both longitudinal and lateral CA, but how much will partly depend on pupil diameter, which in turn determines the focal ratio but, also the collective aberrations through both optical imperfections and anatomical deviations in the retinal surface. The reason we do not normally 'see' these inherent aberration is not primarily optical or anatomical but psychological. Our brains normally corrects the CA, adjusts colour balance, masks optical imperfections and adds in any missing bits it thinks we might like. The whole of 'vision' is just a perception. How much binoculars will affect our interpretation, which I understand, is partially determined by prior experience, but also modified substantially by other psychological inputs. A visual reality check can be quite a sobering experience. ;-)

Hope that explains my earlier post. It's a fascinating subject but confess I struggle with many of the finer points of visual function, and particularly the signal processing pathways and how they may alter what we think we see.

David

off topic

typo said:

The 60 dioptre value is usually quoted as the total corrective power of the eye including focal accommodation, but of course, that will reduce with age. Various sources suggest the lens to retina distance may range from about 19mm to about 27mm and usually come up with between 22mm and 24mm as the modal value.

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I don't know, David. I think you're getting a little confused with diopter and focal length.
60 diopters = 16.66 .. mm = focal length of the eye.
60 diopters are measured at rest without accommodation, as the focal length of a lens is measured, when the fire is placed at infinity.
I know this is just a convention, but that's it, and let's use it.
The distance of the lens (crystalline or corneal? - distance from the front or back surface? Distance from the optical center?) Has nothing to do with it. The equivalence of the lens of the eye and therefore of its dioptric power or focal length, is given by the whole set of cornea, crystalline, vitreous humor, etc., up to the retina.
Why do you want to measure the distance of the lens from the retina?
The average eyeball diameter of a normal person is given as about 24mm. If it were 19mm or 27mm we would have problems with hypermetropia or myopia, respectively.

Sorry Rico, I now realise I misunderstood what I was told by my wife's surgeon. She spoke about the particular need for an accurate posterior chamber measurement for my wife and I wrongly presumed this was the dimension she was referring to when she mentioned an axial length of 21.5mm. This was also close to published values for published infinity focal lengths. Seemed to correspond nicely, but I should have checked. The replacement lens was 22.0d in one eye and 22.25d and is now close to ementropic with uncorrected 6/5 VA in both eyes.

I've checked various sources again and see the lens to retina distance was at one time incorrectly quoted as the focal length in various sources at around 17mm. More current sources suggest focal length is approximately 22mm, or close to the axial length for infinity and would correspond to about 45d. With maximum focal accommadation of around 15d the object focal distance would be about 16.5mm for 60d is again commonly mentioned, as I said before.

I also see that some sources appear to state that the eye's dimensional parameters are constant, and others state that they are variable with age, gender and race. A surprising number of inconsistancies, and yes, rather confusing. Not that any of this makes much practical difference to retinal levels of CA and it's perception.

David

To close, we can say that the CAs in the eye depend mainly on the pupil (iris hole) and on the focal ratio, as in any optical system (photographic lens or binocular, magnifying glass or binocular eyepiece, etc.) and not from the brain or from the post-optic perceptual system.
The CAs of the eye are often invisible, but the most visible are caused more by the stronger contrasts, both in light and in the blur of objects. And they tend to have blue, yellow and red colors.
The accommodation of the eye will automatically tend to deter these effects. And in fact, at the precise moment we try to fix (to observe) a chromatic aberration, the eye system will adjust accordingly to eliminate it.

Spherical aberrations are much more pronounced than CAs. These are also often solved with the regulation of the iris and the accommodation of the crystalline lens.

For us observers and viewers of binoculars, it is very important to understand how our sight works and possibly also our equipment.

David, thanks for the exchange. : T:

Here's a chart showing the accommodation ability of the human eye plotted against age: https://en.wikipedia.org/wiki/Accommodation_(eye)#/media/File:Duane_(1922)_Fig_4_modified.svg. The average 10 year-old with an accommodation of 13 dioptres would be able to focus between 8 cm and infinity.

Although the anterior-posterior diameter of the eye is about 24 mm, its focal length when focussed at infinity is about 17 mm, as Rico pointed out.

John

John,

Rico was kind enough to send me a link to the article he used for his information. It's in Italian but on this occasion Google translate does a reasonable job.
http://www.oculistanet.it/ottica-fisiop/ottica-fisiop-6.htm

It's actually rather useful. In the first illustration you will see the two focal lengths, f1 and f2 marked. Later in the document you will see under Focal Distance these are given as 16.2 and 24mm respectively.(Of course an individual's values may differ). The 24mm is the image focal distance and the pertinent value here. However you will find many articles that list 16 -17 mm as the image focal distance, state it is the cornea to retina distance or supplement the calculation with the close focus dioptre value to make the numbers add up. A bit of a muddle! Although I was wrong footed by the surgeons comments initially, the artical does agree with my revised understanding. I hope we've got there in the end?

David

The one who is born round, cannot die square.